Upload
nguyenhuong
View
262
Download
11
Embed Size (px)
Citation preview
1
OHSP ONLINE LESSON TEMPLATE
SCIENCE GRADE 7 MODULE NO. : Physics: Electricity MODULE INTRODUCTION AND FOCUS QUESTION(S): During thunderstorms, should we be more afraid of the thunder or the lightning? Why? Have you experienced “statics” while combing your hair or when touching a computer’s monitor? Did you experience some sort of shock? How can we protect ourselves from electric shock? Find out the answers to these questions in this module. More importantly, you will learn how to be safe from electric shocks. You will also learn how the science of charges and charging is being used in making our lives better. MODULE LESSONS AND COVERAGE: In this module, you will examine these questions when you take the following lessons: Lesson 1 – Charges and charging processes
What are charges? How do bodies become charged? Lesson 2 – Interactions between charged bodies
How do charged bodies interact with each other? Lesson 3 – Safety with charges
What does it mean that some appliances need to be grounded? How does a lightning rod protect us from harm? Lesson 4 – Applications of charges and charging processes
How are these concepts on charges applied in industries and in cleaning up the air?
In these lessons, you will learn the following: Lesson 1 – Differentiate the three kinds of charges, in terms of protons and
electrons. Discuss and demonstrate how objects become charged. Lesson 2 – Describe and predict how charged and uncharged bodies interact
with each other. Lesson 3 – Investigate how grounding is implemented in appliances. Discuss how lightning rods keep us safe during storms. Lesson 4 – Investigate and report on how concepts on charges are applied in
industries and in cleaning up the air.
2
Here is a simple map of the above lessons you will cover:
To do well in this module, you need to remember and do the following: 1. Open the indicated interactive simulations. Go beyond the given instructions
and questions. Explore further and deeper as your time allows. 2. Open and view the indicated videos. Review the videos as many times as
needed, as you answer the discussion questions related to them. 3. Gather the materials for the experiments and demonstrations and actually do
them yourself. The actual experiments give you a richer learning experience than just reading the texts and even watching related videos.
4. Take down notes as you go through the simulations, videos and experiments. Writing on paper or typing on your computer helps you remember and understand things easier.
NEXT
Lesson 1: Charges and Charging Processes
Lesson 2: Interactions Between Charged Bodies
Lesson 3: Safety with Charges
Lesson 4: Applications of charges and charging processes
3
PRE-ASSESSMENT: Let’s find out how much you already know about this module. Click on the letter that you think best answers the question. Please answer all items. After taking this short test, you will see your score. Take note of the items that you were not able to correctly answer and look for the right answer as you go through this module. 1. The nucleus’ charge is ______ because _____. A. neutral ; it has equal numbers of positive and negative charges B. neutral ; all charges are outside the nucleus C. positive ; it has positively charged protons and uncharged neutrons * D. negative ; it has more electrons than protons
The nucleus is positive because it has protons in it. The negatively charged electrons are outside the nucleus.
2. A sodium ion, Na+ has a net charge of +1 because ______. A. it has only one proton B. it has one less electron than protons * C. it has one less proton than electrons D. it gained one more proton from another atom
A sodium atom has 11 protons in its nucleus and 11 electrons outside. It easily gives off its one outermost electron, and so it has one less electron than protons, becoming a Na+ ion.
3. If a neutral metal sphere (X) is placed in contact with a positively charged
metal sphere (Y), sphere X will _____. A. remain neutral B. become positively charged as well * C. become negatively charged D. fluctuate from being positively charged and negatively charged
The positively charged sphere (deficient of electrons) will take some electrons from the initially neutral sphere. This will make the initially neutral sphere also deficient in electrons and therefore positively charged.
4. In charging by induction, a charged body (X) is placed near to a neutral body
(Y) that is to be charged. If X is negatively charged and Y is connected to the ground, Y will _____.
A. remain neutral B. become positively charged *
X Y X Y X Y
4
4. In charging by induction, a charged body (X) is placed near to a neutral body (Y) that is to be charged. If X is negatively charged and Y is connected to the ground, Y will _____.
A. remain neutral
B. become positively charged * C. become negatively charged as well D. fluctuate from being positively charged and negatively charged
Body X will cause electrons in body Y to move away to the side far from body X. With the grounding, electrons will flow out from body Y.
5. Grounding works by having a negatively charged body _____. A. release excess electrons to the ground * B. take in more electrons from the ground C. take in more protons from the ground D. release excess protons to the ground
Only electrons can be added or removed from bodies. A negatively charged body has excess electrons. When grounded, these excess electrons will flow to the ground until the body becomes neutral.
5
6. Which of the following most needs to be grounded? A. flat iron B. laptop C. TV D. washing machine *
The pulsator in the wash tub gets turned by the motor through a rubber belt. The occasional rubbing between the metal and the rubber belt causes electrostatic charging. The charge build-up could give the user an electric shock. Grounding the washing machine prevents charge from building up.
7. Lightning rods are placed _____ of a building. A. at the base
B. above the windows C. above the highest point
D. on all the corners of the rooftop
Placing rods above the highest points of a building will ensure that if ever lightning strikes, it hits the lightning rod, and not any other part of the building.
8. A lightning rod works by _______. A. conducting the charge to the ground, through the building B. conducting the charge to the ground, bypassing the building * C. collecting the charge into a storage device, for use later as electricity
The charge from lightning is immediately conducted down into the ground, bypassing the building, keeping the people inside the building unharmed. If the lightning rod is not grounded, then electricity will pass through the building and the people in it will not be safe. The great amount of charge cannot be stored (yet) for later use as electricity.
6
9. A single electron’s charge is – 1.6 x 10-19 Coulomb. How will an initially neutral body be made to have a charge of –1.0 microCoulomb?
A. have it gain 6.3 X 1012 electrons * B. remove 6.3 X 1012 electrons from it C. have it gain 1.6 X 1013 electrons D. remove 1.6 X 1013 electrons from it
Q = n qe where Q is the charge developed n is the number of electrons qe is the charge of an electron
n = Q / qe = ( - 1.0 x 10-6 Coulomb) / – 1.6 x 10-19 Coulomb per electon
n = 6.3 X 1012 electrons
This number of electrons will have to be gained by an initially neutral body for it to have a – 1.0 microCoulomb charge.
For items 10 and 11, refer to the triboelectric series in the box at the right:
10. What charges will be acquired by PVC and wool
rubbed with each other? A. PVC: positive; wool: negative B. PVC: negative; wool: positive * C. both will have positive charges D. both will have negative charges The PVC will gain electrons from the wool. 11. Which rubbing material will create the most charge on a glass rod? A. fur B. human hair C. silk * D. wool
From among the choices, silk is lowest in the series, thus having the greatest tendency to gain electrons. The more electrons drawn out from the glass rod, the greater the charge created in it.
leather glass
human hair wool fur silk
rubber styrofoam
polyvinylchloride (PVC)
Increasing tendency to gain electrons
7
12. The picture at the right shows a green wire attached to the motor at the underside of a washing machine’s wash tub. To where does the other end of this wire connect to?
A. to the motor of the spinner tub
B. to the water pipes outside * C. to the dial-switch-timer D. to the plug
The green wire is a grounding wire. Its other end should be connected to the water pipe outside the machine. This way, charge is prevented from building up in the washing machine.
13. What could happen if this wire is not firmly
connected at either ends? A. The motor for the wash tub will run, but that for the spin dryer will not. B. The washing machine will not run. C. The motor will keep running even as the timer goes down to zero. D. The person using the machine might get an electric shock. *
If the grounding wire is not connected, then the charge that may accumulate in the machine may cause an electric shock on the person using it.
14. Why would it be dangerous for people to be out in the open fields during heavy rains and thunderstorms?
A. They might get struck by lightning. *
B. They might get sick with colds and flu. C. They might get stranded in the ensuing flood. D. They might get carried away by the strong winds.
People in open fields (with no trees or houses) are at risk of getting struck by lightning. The other risks above should also be avoided, but the most fatal of them is the first.
8
15. Pictured below is the process by which an electrostatic precipitator reduces the pollutants releases to the atmosphere by factories. For this eco-friendly device to work, what should be the charge of the metal grid and the collecting plate?
A. Both should be positively charged. B. Both should be negatively charged. C. It will work as long as they have opposite charges. *
D. The grid could be neutral, as long as the collecting plate has a strong positive or negative charge.
If the grid is positively charged, the smoke particles will become positively charged. To attract the charged smoke particles, the collecting plates will have to be negatively charged. If the grid is negatively charged, the smoke particles will become negatively charged. To attract the charged smoke particles, the collecting plates will now have to be positively charged.
Collecting
plates
Metal grid
Smoke particles
become
charged
9
16. You conducted a “magic show” with the kids in an orphanage you visited. You showed them the demonstration where tissue bits flew up to the plastic sheet. How would you best explain to the kids why the tissue bits moved up, defying gravity? Assume the plastic sheet to be negatively charged.
A. The tissue bits are neutral, and so it was attracted by the charged
plastic sheet. B. While on the table, the tissue bits got induced to have a positive
charge. C. While on the table, the tissue bits got polarized with its upper side
positively charged. * D. The plastic sheet induced a positive charge on the table top, and this
repelled the tissue bits.
The negatively charged plastic sheet repels the electrons in the tissue bits, pushing them lower. This polarizes the tissue bits, with the upper side positively charged, and the lower side negatively charged. The tissue bits however are still electrically neutral. (Left figure below) With the tissue bits now polarized, the upper side gets attracted to the plastic sheet. The attraction overcomes the repulsion that the lower side experiences. (Right figure below)
Table top
Plastic
sheet
- - -
-
-
+ + + + +
- -
- -
- -
- -
-
+
- -
- -
- -
- -
10
17. You then touched the top side of the plastic sheet where there are tissue bits
under it. What would have happened, and why?
A. The tissue bits stay attached to the bottom of the plastic sheet. Your finger has no effect on the charges in the objects.
B. The tip of your fingers also got polarized to have a partial positive charge, and your finger repels the tissue bits.
C. Your fingertip grounds the plastic, so it becomes neutral and thus no longer attracting the tissue bits. *
D. Your fingertip makes the plastic have a positive charge, and so it then repels the tissue bits.
Touching the plastic sheet grounds the plastic, at least the point touched. This point becomes neutral, and so no longer able to attract the tissue bit. Option B is not possible, as your hand is connected to your body, and is connected to the ground. The small plastic sheet can polarize a smaller object, but not a bigger body that is connected to the ground. Option D is not possible. There is no way for the finger to cause the plastic sheet to have a positive charge. The finger can take away just enough electrons to make it neutral, but not to make it positively charged.
Table top
Plastic sheet
11
18. The picture at the right shows a 2-prong plug and 2-hole outlet, and a 3-prong plug and 3-hole outlet. Your uncle is finishing his house, and he asks you which type of outlet he should install. What will you tell him and why?
A. Install just 2-hole outlets. For appliances with 3-prong plugs, he may just use adapters.
B. Install just 3-hole outlets. Both 3-pronged and 2-pronged plugs will fit in these outlets.
C. Install 2-holed outlets where it is needed: for the stove, oven, shower heater; and 3-hole outlets elsewhere.
D. Install 3-holed outlets where it is needed: for the stove, oven, shower heater; and 2-hole outlets elsewhere. *
Appliances with heating elements (stove, oven, shower heater) are prone to accumulating charges that may cause electric shock. The third prong actually connects to a grounding wire inside the round hole in the 3-hole outlet. Most other appliances do not need grounding, and so they only have 2-prong plugs and will need just 2-hole outlets. Remember, it is not just a matter of having a 3rd hole for the 3rd prong. The grounding wire inside the third hole is the key protective device against shocks. Thus, Option B is dangerous if you have ungrounded 3rd holes in outlets in your living room. Plugging in your stove there will not ground your stove. Option A is not good, as plugging in 3-prong devices into 2-hole outlets through an adapter does not ground the appliance.
2-hole outlet
3-hole outlet
12
19. Consider the boy at the left side
of the picture. How would the hazard he is exposed to be eliminated?
A. The tree’s branches near the
power lines should be trimmed. *
B. The sign “No climbing” should be nailed onto the tree.
C. A playground should be built on the open area.
D. He is not exposed to any hazard. As long as he doesn’t touch the power lines, he’ll be alright.
If the branches touch the power lines, the boy is at risk of getting
electrocuted, especially when it rains. 20. If you are the safety engineer in the town where this picture was taken, what
would you do? Write below concrete actions to make this area of your town safer.
________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
Safety signs could be placed at the grounds near the power lines: “No flying of kites.” Remind residents to not let electrical wires and appliances near bodies of water like in kiddie pools. Trim the trees near the power lines. Do not let branches grow near the power lines.
NEXT
13
Lesson 1 Charges and Charging processes
In this lesson, you shall:
Differentiate the three kinds of charges, in terms of protons and electrons.
Discuss and demonstrate how objects become charged. EXPLORE:
In this lesson, we will focus on the following questions: What are charges? How do bodies become charged?
1. Pre-reading check. Before plunging into our first lesson, answer the following questions. Click on your answer.
a. The fundamental carriers of negative charge: A. atoms B. electrons * C. neutrons D. protons b. The proton’s charge is _____. A. +1 Coulomb B. – 1 Coulomb C. + 1.6 x 10-19 Coulomb * D. – 1.6 x 10-19 Coulomb
c. A neutral atom _____. A. has no electrons B. has only neutrons in its nucleus C. has equal numbers of protons and neutrons D. has equal numbers of protons and electrons * d. An atom becomes a positive ion when it _____. A. gains one or some electrons B. loses one or some electrons * C. gains one or more protons D. loses one or more protons e. An atom becomes a negative ion when it _____. A. gains one or some electrons * B. loses one or some electrons C. gains one or more protons D. loses one or more protons
14
1.2 Webpage reading: Atomic Structure Did you get all the correct answers? Review the items where you had mistakes. Keep them in mind as you read the webpage on atomic structure: http://web.jjay.cuny.edu/~acarpi/NSC/3-atoms.htm
Open the page below to know more about electrons: http://www.windows2universe.org/physical_science/physics/atom_particle/electron.html Click on the link to protons to go to another page, or open this: http://www.windows2universe.org/physical_science/physics/atom_particle/proton.html
Do you now understand how atoms become charged? Sub-atomic particles are charged,
and so atoms are either positive negative or neutral, depending on the numbers of
protons and electrons in them.
1.3 Comprehension Check: How atoms get charged To summarize the key ideas from the readings, complete the statements below by clicking and dragging in the correct tiles from below.
1. The particles whose charge is – 1.6 x 10-19 Coulomb: _____.
2. The particles whose charge is + 1.6 x 10-19 Coulomb: _____.
3. The uncharged particles are the _____.
4. When an atom loses electrons, it becomes _____.
5. When an atom gains electrons, it becomes _____.
6. To become charged, atoms can easily gain or lose _____, but not _____.
protons
electrons
neutrons neutral
positively charged negatively charged
electrons
protons
neutrons
neutral
negatively charged
electrons protons
15
1.4 Rubbing Balloons After learning how atoms become charged, let’s now see how objects become charged.
a. Get two rubber balloons. Inflate them. Hang them on strings, about 1 foot long.
b. Rub the balloons on your shirt, blouse, pants, or table cloth. c. Pass the balloon above your forearm. How does it feel? Place it
above your head. What happens? d. Hold the strings together on one hand. Do the balloons repel each
other? e. Tear up a piece of tissue paper into small bits. Hold the rubbed balloon
a few inches above the tissue bits. What happens? f. Hold the rubbed balloon against the wall. What happens? (You may have to rub the balloons again after some time through the
procedures above.) Why is it that rubbing the balloons makes them do some gravity-defying tricks? 1.5 Rubbing Balloons Worksheet
In this worksheet, you will record your observations in the previous activity. Write also in the 3rd column your “guess-planations” (guess-explanations) for each observation.
Procedure / Set-up Observations Guess-planations
Rubbed balloon placed near forearm
Rubbed balloon placed near one’s head
Two rubber balloons, each hung down by their threads
Rubbed balloon placed near tissue bits
Rubbed balloon brought near the wall
Review your Observations and Guess-planations. What do you notice about your answers? What comments are similar? What comments are different? Can you see any pattern to the results that you got? What do you think is a principle at work in these different procedures? Remember that only electrons (and not the protons) can be passed between bodies through ordinary interactions like rubbing and contact. Review your answers, with this key fact in mind.
16
End of EXPLORE: You just tried finding out about charges and how objects become charged. You also gave your initial ideas on why charged objects behave as observed. Let’s now find out more about charges by doing the next activities.
NEXT FIRM UP: Your goal in this section is to learn and understand some key concepts, by working on the following questions:
How do we know what charges objects acquire when they are rubbed together? Which becomes positive? Which becomes negative?
What is the triboelectric series? How was it made or determined? 1.6 Web page reading: Creating Charges with Friction - Triboelectricity
a. Write down your initial answers to these questions:
How do we know which of the two objects rubbed together becomes positively charged?
Which becomes negatively charged?
What pairs of objects will more likely create strong charges in the objects?
b. Open and read this web page: http://regentsprep.org/Regents/physics/phys03/atribo/default.htm
1.7 Triboelectricity: Check for Understanding
Let’s review the ideas found in the Website you just read. Click on your answers to the following questions. 1. Which should your rub with amber to make it positively charged? A. fur B. leather C. styrofoam * D. wool
17
2. Which material, when rubbed with Styrofoam will create the strongest negative charge on Styrofoam?
A. leather * B. PVC C. Teflon D. wool 3. When you rub an inflated balloon with your hair, the balloon
______, your hair _____. A. becomes negatively charged ; stays neutral B. becomes positively charged ; stays neutral C. becomes positively charged ; becomes negatively charged D. becomes negatively charged ; becomes positively charged *
4. Which pairs of materials, when rubbed together, will cause the weakest net charge in them?
A. silk and wood * B. glass and rubber C. scotch tape and PVC D. dry hands and Teflon 5. Which of the following statements most correctly describe the sign
of the charge that objects acquire by rubbing? A. Some objects can become only positively charged, while other
objects can become only negatively charged. B. Objects can become either positively or negatively charged,
depending on the material used to rub them. * C. Soft objects tend to become positively charged, while hard
objects tend to become negatively charged. D. Natural materials tend to become positively charged, while
synthetic materials tend to become negatively charged.
How did you do with this quiz? If you did well, continue to the next part. If not, go back and find out from the reading the reason for the correct answers.
End of FIRM UP: In this section, you have read about how objects become charged either positively or negatively. Go back to the previous section and compare your initial ideas with the discussion in the assigned webpage. How much of your initial ideas are found in the discussion? Which ideas are different and need revision?
Now that you know the important ideas about this topic, let’s go deeper by moving on to the next section.
18
NEXT
DEEPEN: Your goal in this section is to take a closer look at some aspects of the topic. Here you will see some demonstrations on how real charged objects interact. From their interactions and from your prior readings, you will decide on the charges of these objects.
1.8 Video Analysis: Rotating Straw
Open this video: http://www.youtube.com/watch?v=Ne7oqESE5Zw
Re-view the video, pausing it every now and then so you can take down notes. When done, answer the following questions. Video Analysis Worksheet: “What’s my charge?” As you review the video, fill in the table below.
Material …rubbed with Interaction with rotating straw (attracted or
repelled)
The objects are therefore charged (+ or -)
How did you decide on the charges of the objects? Did you actually see whether objects are in excess or deficient of electrons? Or did you have to rely on the observed interactions and the triboelectric series? Explain. 1.9 Positive or Negative?
19
Review the triboelectric series in this page: http://regentsprep.org/Regents/physics/phys03/atribo/default.htm Gather as much materials in the list that you can gather. Choose different pairs of objects to rub together. If you have access to an airconditioned room (low humidity), perform this activity there. Humidity will cause the rubbed objects to more quickly discharge, thus the effects will not be observable. Determine the charges of the rubbed objects by seeing how they affect either a charged straw that is free to rotate (like in the video) or a charged strip of plastic cover that is hung and free to swing towards or away an object placed near it. (e.g. If the object repels the negatively charged plastic strip, then it is also negative. If the strip is attracted, then the object is positively charged.) Fill the table below:
Pair of objects rubbed
Charges of the objects, as predicted using the triboelectric series
Effect on the straw or plastic strip (attract or repel)
Charge of the objects, based on interaction with straw or strip
1
2
3
4
5
Did the objects behave as predicted by the triboelectric series? Or were there any discrepancies? What could have caused these discrepancies? Go back to the reading on the triboelectric series as you review your ideas. End of DEEPEN:
20
In this section, you saw demonstrations on how charged objects interact with each other. You then inferred the charges of these objects from the observed interactions. What new realizations do you have about the topic? What new connections have you made for yourself? Now that you have a deeper understanding of the topic, you are ready to do the tasks in the next section.
NEXT
TRANSFER: Your goal in this section is apply your learning to real life situations. You will be given a practical task which will demonstrate your understanding. 1.9 Make your own demo! Explore other related videos on electrostatic interactions in You Tube. See which demonstrations you can do yourself. Can you come up with your new demonstrations with materials that are available to you? Try to come up with demonstrations that are:
interesting especially for kids
replicable (even by kids) and safe
effective for teaching others about charges Maybe you will want to video your demonstrations and upload them to You Tube and be the next You Tube discovery!
End of TRANSFER: In this section, your task was to create your own demonstration on electrostatic charging. This performance task is just a practice and preparation for the more exciting and relevant performance tasks in the next lessons. How did you find the performance task? How did this task help you further understand the science of charges and the interactions between charged bodies? Write down your reflections on your notebook or on a journal file in your computer. You have completed this lesson. Before you go to the next lesson, you have to answer the following post-assessment. If you pass this test, you may move on to
21
the next lesson. If you do not pass this test, you may go back and review the lesson and take this test again.
NEXT
CHECK-UP TEST:
1. The fundamental charges in nature are the _____ and the _____. A. protons ; electrons B. electrons ; neutrons C. atoms ; protons D. neutrons ; protons 2. Objects that are not charged are also said to be _____. They have _____. A. neutral ; no electrons and protons B. neutrons ; less protons than electrons C. neutral ; equal numbers of protons and electrons D. natural ; more neutrons than protons and electrons 3. To become charged, objects need to either lose or gain _____. A. protons B. electrons C. neutrons 4. The nucleus’ charge is ______ because _____. A. neutral ; it has equal numbers of positive and negative charges B. neutral ; all charges are outside the nucleus C. positive ; it has positively charged protons and uncharged neutrons * D. negative ; it has more electrons than protons 5. A sodium ion, Na+ has a net charge of +1 because ______. A. it has only one proton B. it has one less electron than protons * C. it has one less proton than electrons D. it gained one more proton from another atom 6. When you rub an inflated balloon with your hair, the balloon ______, your hair
_____. A. becomes negatively charged ; stays neutral B. becomes positively charged ; stays neutral C. becomes positively charged ; becomes negatively charged D. becomes negatively charged ; becomes positively charged * 7. When two objects repel, then they surely are _____. A. both positively charged B. both negatively charged C. both of the same charge
22
D. of opposite charges 8. If you rub two objects together, how will you know which one becomes
positively charged, and which one becomes negatively charged? A. The rougher object becomes positive, the smoother one becomes
negative. B. The shinier object becomes positive, the duller one becomes negative. C. The rubbed object becomes negative, the other becomes positive. D. Check how the rubbed object interacts with other objects of known
charge.
For items 9 and 10, refer to the triboelectric series in the box at the right:
9. What charges will be acquired by PVC and wool
rubbed with each other? A. PVC: positive; wool: negative B. PVC: negative; wool: positive * C. both will have positive charges D. both will have negative charges The PVC will gain electrons from the wool. 10. Which rubbing material will create the most charge on a glass rod? A. fur B. human hair C. silk * D. wool
NEXT
leather glass
human hair wool fur silk
rubber styrofoam
polyvinylchloride (PVC)
Increasing tendency to gain electrons
23
Lesson 2 Interactions between charged bodies
In this lesson, you shall:
Describe and predict how charged and uncharged bodies interact with each other.
Discuss the different charging processes: conduction, induction and polarization.
EXPLORE: Are you ready to learn more about charges and how they interact? Let’s explore! In the previous lesson, you learned how a body becomes charged. In this lesson we focus on the following question: How do charged bodies interact with each other?
2.1 Web-page reading: Attraction and repulsion You saw in the first lesson how different combinations of charged bodies either attract or repel each other. Read the following page to review some ideas, and to ready you for further for this new lesson. http://www.gcsescience.com/pse3-electrostatic-charge-attraction-repulsion.htm
How about neutral objects? How come they also get attracted to charged bodies? Write down your initial explanation as to why neutral bodies behave as such.
Then go on to read this page: http://www.gcsescience.com/pse5-electrostatic-charge-neutral-attract.htm
Let’s do a comprehension check on what you just read. Click on the T if the statement is TRUE. Click F if the statement is FALSE.
1. Bringing a charged body near a neutral body will cause it to become charged.
2. Bringing a positively charged body close to a neutral body will cause
electrons to rush to the side near the positively charged body. 3. Bringing a negatively charged body close to a neutral body will cause
protons to rush to the side near the positively charged body.
T F
T F
T F
24
Let’s now find out in the next part what the answers to these questions are. 2.2 Charging balloons. Interactive simulation exploration. Recall what you did in the previous lesson with balloons. You saw how the rubbed balloon interacted with another balloon, your hair, bits of paper, and with the wall. However, we cannot really see the movement of charges into or out of the balloon. Open this interactive simulation:
http://phet.colorado.edu/en/simulation/balloons (You may have to install a Java program for the simulation to play.)
As you explore the animation, keep in mind these questions: a. What charge occurs in the balloon after it is rubbed on the sweater? b. What net charge does the sweater therefore acquires?
c. What transfers between bodies to cause these bodies to become charged?
d. What happens between objects with unlike charges? e. What happens between objects with like charges? f. Explain why the charged balloon sticks to the wall. Was the wall
charged? Again, note down answers in your notebook or note-file.
End of EXPLORE: At the start of this lesson, you reviewed the basic interactions between charged objects. You then learned how neutral objects can get attracted to charged objects, even as they stay neutral. The redistribution of electrons in the neutral body allows it to be attracted by (or to attract) charged bodies. Go back to the three TRUE-or-FALSE questions in Activity 2.1 and see if you are now convinced of the correct answers. In the next activities, you will see and use simple devices that can detect the presence of charges.
NEXT
25
FIRM UP: Your goal in this section is to learn and understand these key concepts:
An electroscope is a device used in detecting the presence or absence of charge.
Objects can be charged by conduction or induction.
Keep in mind these questions as you do the next activities:
What happens when a charged body is brought near a neutral body?
Besides rubbing, through what other ways can bodies be charged?
2.3 An electroscope
Read the following webpage: http://www.gcsescience.com/pse4-electrostatic-gold-leaf-electroscope.htm Then watch this video: http://www.youtube.com/watch?v=2PmWlPjV6n0&feature=fvwrel Check your comprehension through the following questions: 1. The electroscope is a device used to ______. A. see charges B. detect charges in bodies * C. measure the amount of charges in bodies D. count the number of electrons going in or out of bodies 2. Identify the parts of the electroscope. Click and drag the names to the right boxes.
Cap or knob
Leaf
Insulation
Conducting stem
26
Alternate item, if above item cannot be programmed: 2. Which of the following items can be used as the stem for the electroscope? A. a plastic spoon B. a popsicle stick C. a metal paperclip with its plastic coating intact D. a metal paperclip with its plastic coating at its ends removed 3. The foil leaf repels when ______ is placed near its knob or cap. A. a person’s hand B. a positively charged body C. a negatively charged body is placed near D. a charged body, either negative or positive * 4. If a negatively charged body is brought near the knob or cap, the leaves
become _____ and they _____. A. positively charged ; attract B. negatively charged ; attract C. positively charged ; repel D. negatively charged ; repel * 5. If a positively charged body is brought near the knob or cap, _____. This
makes the leaves _____. A. electrons go up from the leaves to the knob; negatively charged B. electrons go down from the knob to the leaves; negatively charged C. electrons go up from the leaves to the knob; positively charged * D. electrons go down from the knob to the leaves; positively charged
2.4 Hands-on: Make your own electroscope
After having watched how an electroscope can be made, try doing it yourself! Here’s another good video on how to make an electroscope. Pay attention to some details that will help make sure your electroscope will work. Click on the link to watch the video found at http://www.youtube.com/watch?v=jBF-144bV18&feature=related
Case or cover
27
2.5 Electroscope charging and grounding, explained After making your own electroscope, get to know further how it works. Watch this video:http://www.youtube.com/watch?feature=endscreen&NR=1&v=-JsVZwc1dOo. Take down as much notes as you can as you watch the video.
2.6 Video viewing analysis worksheet Fill in the table below. Draw sketches of the spaces given.
Process description Diagram Explanation Charge of the leaves
(at the end of process)
1) Vinyl (negatively charged) is brought near to the knob and the leaves repel.
2) Vinyl is brought away and the leaves fall back down.
3) Vinyl is brought near again, and then finger touches the knob while the charged object is still held near.
4) Vinyl is then moved away and the leaves repel.
5) Vinyl is brought near again, but this time the leaves close.
28
Then when vinyl is brought away, the leaves repel.
6) Glass (positively charged) is brought near, and the leaves repel further.
At the 4:21 mark, the narrator says, “A similar sequence of events happens if you charge it using a positively charged object instead, and then touch it with my finger again.” Try doing these steps with your own electroscope. Then fill up the table below, this time with a positively charged body being used to charge the electroscope.
Process description Diagram Explanation Charge of the leaves
(at the end of process)
1) Positively charged object is brought near to the knob and the leaves repel.
2) Positively charged object is brought away and the leaves fall back down.
3) Positively charged object is brought near again, and then finger touches the knob while the charged object is still held near.
4) Positively charged object is then moved away and
29
the leaves repel.
5) Positively charged object is brought near, but this time the leaves close. Then when object is brought away, the leaves repel.
6) Negatively charged object is brought near, and the leaves repel further.
Was it easy to provide a different set of explanations to the apparently very identical
observations? What did you notice about your explanations?
Keep in mind that only electrons can be moved within and between bodies to cause
bodies to become charged. Recall the three True-orFalse questions at the start of
EXPLORE (Activity 2.1) Compare your initial answers with the results of this activity.
2.7 Webpage readings: Charging processes
Open and read the following websites. Keep in mind the following questions as you read:
How could neutral objects be attracted by charged objects?
What kinds of objects can be used in charging by conduction?
What kinds of objects can be used in charging by induction?
What’s the difference between charging by conduction and by induction?
What is polarization? How does it happen?
How is grounding involved in these charging processes? In this web page, you’ll see how neutral objects get attracted to charged objects. http://www.gcsescience.com/pse5-electrostatic-charge-neutral-attract.htm In the following web pages, you’ll see how neutral objects can be charged through two different processes: conduction and induction. http://www.studyphysics.ca/30/charging.pdf http://www.physicsclassroom.com/class/estatics/U8L2b.cfm http://www.physicsclassroom.com/class/estatics/U8L2c.cfm
30
Re-read the web pages, this time with a pen in hand you write down on your notebook answers to the questions above.
2.8 Hands-on: Charging by induction and conduction Using your home-made electroscope and other materials described in the readings, demonstrate charging by conduction and induction. Have as your audience your siblings, parents, or neighbors. Having them ask questions that you gladly answer will enhance your understanding and mastery of the lesson. End of FIRM UP: In this section, you have further explored charges using a simple device, the electroscope. You have also investigated and discussed conduction and induction, two ways through which objects can become charged. You also encountered grounding, and how it is used as a step in charging or discharging bodies. So now, explain in your own words how neutral objects can be attracted to charged bodies. Please also explain how bodies can become charged through conduction and induction? Finally, explain what kinds of bodies can be charged through conduction and / or induction. If you have difficulty explaining, go back to the readings and Web pages in this section!
Now that you know the important ideas about this topic, let’s go deeper by moving on to the next section.
NEXT DEEPEN: Your goal in this section is to take a closer look at some aspects of the topic. Here you will complete two worksheets that will check on your understanding of the charging processes. You will then read Web pages that further elaborate how even neutral objects participate in electrical interactions simply because they are polarized.
31
2.9 Worksheets: Charging processes Using your home-made electroscope and other materials described in the readings, demonstrate charging by conduction and induction. Then open the web page below and answer the worksheet. http://dev.physicslab.org/Document.aspx?doctype=5&filename=Compilations_CPworkbook_ElectrostaticsConductionInduction.xml See the notes and questions that further clarify the differences between conductors and insulators, and how each of these kinds of materials can be charged. You may re-open the websites in the previous activity to help you answer the questions in this worksheet. Worksheet: 3-ele-01_charging_by_induction.doc
CHARGING BY INDUCTION
You can charge objects by a process called induction. You don’t need
to actually touch the object with some other already charged material but just bring it in close proximity. The force then acts from a distance
and induces the charge.
The two spheres are made out of metal because metals have many free electrons that can easily move and are good conductors of
electricity. We also need to use a non-conducting strip of material that we can charge by friction.
1. Before the experiment is begun, will the metal spheres and the
strip be charged or uncharged? This is now tested with the coulombmeter. What does it tell you about the charge of both
spheres?
2. What material is being used for friction charging?
32
3. What kind of charge will be on the strip after it has been rubbed
with the duster?
Now the strip is charged by rubbing it vigorously with a duster.
Follow the sequence of events in the demonstration as shown below and mark on the diagrams what happens to the charge as the
experiment progresses. At first the metal spheres are touching but the charged strip is well away from them.
I. Uncharged metal spheres, where are the positive and negative
charges?
A B
33
II. The charged strip is brought near to but not touching one of the
metal spheres A.
III. Keeping the charged strip near to sphere A, separate the metal
spheres.
IV. Remove the charged strip.
V. Checking the charge on metal spheres A & B.
Charge on A / nC
Charge on B / nC
a. What kind of charge has moved? ………………………………….
b. Where did the charge move? from…………………………………to………………………………….
A B
B A
A B
34
c. What would you expect to happen if A and B are made to touch
again?
2.10 Webpage reading: Polarized objects and molecules Review the webpage below: http://www.gcsescience.com/pse5-electrostatic-charge-neutral-attract.htm The word polarized is not mentioned in the page. However, see that the neutral object has its charges not evenly distributed. This body is polarized by the charged body brought near it. Some electrons are repelled down to its bottom part, leaving the upper part positively charged. The whole body is still electrically neutral. This body is polarized, as it has positively charged and negatively charged sides or ends. Read the page below. Explore the page, and see for yourself why water is so essential and called the universal solvent. Click on the following site: http://www.edinformatics.com/interactive_molecules/water.htm Note that dissolving things is also dependent on the electrical properties of molecules!
End of DEEPEN: In this section, you strengthened your understanding of the different charging processes. You then read about how even neutral bodies participate in electrical interactions. What new realizations do you have about the topic? What new connections have you made for yourself? Now that you have a deeper understanding of the topic, you are ready to do the tasks in the next section.
NEXT
35
TRANSFER: Your goal in this section is apply your learning to real life situations. You will be given a practical task which will demonstrate your understanding.
2.11 Jumping and floating beads video analysis
Watch this video: http://www.youtube.com/watch?v=7LxyA-7KIoo With what you have been learning so far about charging processes, provide an explanation as to why the beads jump, hover and float, as if by magic. Compare notes with other on-line learners. How are your explanations similar to theirs? How is your explanation different? Give some feedback to the other learners, and see how you can convince them to your explanation. On the other hand, it may be that it is you who’ll need to be convinced to their explanation!
2.12 Lab Activity: Flying tissue bits Perform the following procedures that approximate the effects you saw in the video. Cut or tear some small bits and strips of tissue paper. Let these bits of tissue lie on the tabletop. Get a bond-paper sized plastic sheet (what we use for covering books and notebooks) and rub it with cloth or tissue paper. Hold it horizontally a few centimeters above the tissue bits. Observe closely.
Again, as with the beads in the video, compose an explanation for your observations.
End of TRANSFER: In this section, your task was to create another demonstration on electrostatic charging and to provide deeper explanations as to how these effects happen in terms of the unseen charges within these objects. How did you find the performance task? How did this task help you further understand the science of charges and the interactions between charged and even neutral bodies? Write down your reflections on your notebook or on a journal file in your computer. You have completed this lesson. Before you go to the next lesson, you have to answer the following post-assessment. If you pass this test, you may move on to the next lesson. If you do not pass this test, you may go back and review the lesson and take this test again.
NEXT
36
2.13 Lesson 2 Quiz 1. When a positively charged body is brought near a neutral body, the neutral
body’s near side becomes _____, while the far side becomes _____. A. negative ; positive * B. positive ; negative C. positive ; also positive D. negative ; also negative 2. When a negatively charged body is placed near an electroscope’s knob,
electrons _____, and the leaves become _____. A. move upward to the knob ; positively charged B. move upward to the knob ; negatively charged C. move downward to the leaves ; positively charged D. move downward to the leaves ; negatively charged * 3. Metals are typically charged by _____, because they have _____. A. induction ; lots of excess electrons B. rubbing ; a strong capacity to gain electrons C. grounding ; a strong tendency to release electrons to the ground D. conduction ; free electrons that can move from one body to another * 4. When charged non-metallic objects are used to charge another body, what
happens is _____ because _____. A. conduction ; the bodies are touching each other
B. induction ; the bodies are not really touching each other C. induction ; non-metals cannot pass electrons between them D. conduction ; non-metals can also pass electrons between them
5. Touching the electroscope knob while a positively charged body is near it will
cause electrons to go _____, and the leaves become _____. A. into the knob from the finger ; positively charged B. into the knob from the finger ; negatively charged * C. out of the knob and into the finger ; positively charged D. out of the knob and into the finger ; negatively charged 6. Touching the electroscope knob while a negatively charged body is near it will
cause electrons to go _____, and the leaves become _____. A. into the knob from the finger ; positively charged B. into the knob from the finger ; negatively charged C. out of the knob and into the finger ; positively charged * D. out of the knob and into the finger ; negatively charged
37
7. A positively charged sphere W is brought near two neutral metal spheres X and Y that are touching each other. Sphere Y was then brought away to the right, removed from its contact with sphere X while sphere W is still near sphere X.
What will be the charges of spheres X and Y? A. X becomes negatively charged ; Y stays neutral B. X becomes positively charged ; Y stays neutral C. X becomes positively charged ; Y becomes negatively charged D. X becomes negatively charged ; Y becomes positively charged * 8. A negatively charged sphere W is brought near two neutral metal spheres X
and Y that are touching each other. Sphere Y was then brought away to the right, removed from its contact with sphere X while sphere W is still near sphere X.
What will be the charges of spheres X and Y? A. X becomes negatively charged ; Y stays neutral B. X becomes positively charged ; Y stays neutral C. X becomes positively charged ; Y becomes negatively charged * D. X becomes negatively charged ; Y becomes positively charged
+
+ + +
W Y X
+
+ + +
W Y X
? ?
-
- - -
W Y X
-
- - -
W Y X
? ?
38
9. A negatively charged sphere W is brought near two neutral plastic spheres X and Y that are touching each other. Sphere Y was then brought away to the right, removed from its contact with sphere X while sphere W is still near sphere X.
What will be the charges of spheres X and Y? A. X becomes polarized ; Y stays neutral * B. both X and Y become positively charged C. both X and Y become negatively charged D. X becomes positively charged ; Y becomes negatively charged 10. A negatively charged plastic sheet, when brought near tissue bits on top of a
table, will cause the tissue bits to become _____.
A. entirely positively charged B. entirely negatively charged C. polarized, with the top side positive and the bottom side negative * D. polarized, with the top side negative and the bottom side positive
NEXT
-
- - -
W Y X
-
- - -
W Y X
? ?
39
Lesson 3 Safety with Charges
In this lesson, you will do the following: Investigate how grounding is implemented in appliances. Discuss how lightning rods keep us safe during storms.
Keep in mind the following questions as you move on:
How do the charging processes happen in some appliances at home?
What does it mean that some appliances need to be grounded?
How does grounding work to keep us safe?
How does a lightning rod protect us from harm?
EXPLORE: Let’s continue with Lesson 3 of this module! In the previous lesson, you learned how charged bodies interact with each other. In this lesson, we will focus on the following questions: What does it mean that some appliances need to be grounded? How does a lightning rod protect us from harm?
3.1 Webpage reading: Lightning Open and read this webpage on electrostatic shock, an introduction to lightning: http://www.gcsescience.com/pse6-electrostatic-charge-shock-spark-danger.htm Now go on to read more about lightning: http://environment.nationalgeographic.com/environment/natural-disasters/lightning-profile/ What new learning did you get from the readings? What are still unclear? Write notes on your notebook or note-files, both key insights and questions that you have in your head. Go back to these notes as you move on to the next activities.
3.2 Interactive animation on lightning Go to this site where you’ll see simulations of the effects of lightning: http://environment.nationalgeographic.com/environment/natural-disasters/lightning-interactive/ From the experience with the interactive animation, think through the following questions:
How can we be safe in our homes during thunderstorms?
How can we be safe outdoors during thunderstorms?
Will you be safer inside your car or under a tree? Explain.
40
How are lightning formed in the clouds?
You learned in the previous lessons that only electrons get to move around and between bodies. Is there anything in the animations that seem to contradict this idea? How can this be corrected or improved?
End of EXPLORE: At the start of this lesson, you explored about electric surges and lightning. You now may have new ideas or insights about lightning and safety with electricity. You may also have more questions in your head now after the Webpage readings and the interactive simulation. In the next activities, you will read more about staying safe from lightning.
NEXT
FIRM UP: Your goal in this section is to learn and understand these key concepts:
Lightning rods are devices that keep people safe inside structures that are vulnerable to lightning strikes.
Lightning rods need to be connected to the ground, so that charges will be conducted to the ground, sparing the structure and the people inside from damage.
3.3 Readings on Safety with Lightning Read the following web-pages. As you read, you may need to review your notes from the previous lessons or activities to understand some parts. In this web page, you will read tips on how to be safe during thunderstorms. http://environment.nationalgeographic.com/environment/natural-disasters/lightning-safety-tips/ Learn more about lightning in this web page: http://www.lightning.org/faq?tid=86 This web page has information on how houses are kept safe by properly installed lightning rods: http://www.ehow.com/how-does_4588127_lightning-rod-protect-house.html
41
Check your comprehension of the readings by assessing the following actions during a thunderstorm. Click on the S button if the action is SAFE. Click the U button if it is UNSAFE.
1. Stay indoors during thunderstorms.
2. Take shelter under the tallest tree you can find. 3. Crouch low on the ground. 4. Continue watching television in your house.
5. Stay inside your car when caught outside.
6. Lightning rods need to be properly grounded. 7. One lightning rod is enough to protect a big subdivision.
How sure are you with your answers? Do you have them “know-how” on safety with lightning? Let’s find out the answers to these questions by going to the next part. 1. SAFE. If a thunderstorm starts and you are indoors, stay indoors. Wait it out
before going out to your next destination. 2. UNSAFE. The tallest tree will be most likely hit by lightning. And if you are
under it when it gets hit, charges may also zap to you sideways from the trunk.
3. SAFE. Crouching low on the ground will lessen the risk of getting hit by lightning. Do this only of course if no shelter is within a short run from where you are.
4. UNSAFE. Continuing to use the television during a thunderstorm increases the risk of lightning hitting your house.
5. SAFE. In case your car gets hit by lightning, electricity will be conducted quickly into the ground. Of course, close your windows and don’t be touching your car’s metal body, or else you’ll be unsafe.
6. SAFE. An ungrounded lightning rod is useless. It may even be increasing the risk of damaging the house, as it will cause the discharge to flow through the house.
7. UNSAFE. Even for a big house, more than one lightning rod is needed. What more for a big subdivision.
S U
S U
S U
S U
S U
S U
S U
42
End of FIRM-UP: In this part of the lesson, you learned about how lightning is created, and how we can be safe from lightning. If you did not do well in the comprehension check above, then you may not be very safe when the next thunderstorm happens! Go back and review the readings and the interactive website. You may try looking at other related websites to help further clarify your unserstanding. If you did well (perfect or just 1 mistake), then move on to the next part.
NEXT
DEEPEN: Your goal in this section is to take a closer at another safety mechanism, this time inside your own homes: grounding of some appliances. Here you will read about appliances and their plugs and the outlets where you plug them in. You will also examine your own appliances’ plugs and outlets.
3.4 Webpage readings: Ground wires, 3-prong plugs and 3-hole outlets Open the following web-pages and read on ground wires and 3-prong plugs and 3-prong outlets. As you read, think of the following questions:
Why do some appliances have 3-prong plugs?
Why are some outlets with 3 holes?
What’s the difference with 2-prong plugs and 2-hole outlets?
What is grounding? What is a ground wire for?
How do these things help keep us safe? The web page below discusses the differences between 2-pronged and 3-pronged plugs in appliances, and what the 3rd prong is for. http://electronics.howstuffworks.com/everyday-tech/question110.htm The web page below discusses how the 3-hole outlet should have the grounding connection. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/bregnd.html
Take down notes and answers to the questions in your notebook.
43
3.5 Home-based explo: What appliances have ground wires and 3-prong plugs?
Now that you have read about ground wires and 3-prong plugs and 3-hole outlets, it is time for you to actually look around your house to see these things for yourself. Do the following:
1. List down appliances that have 2-prong plugs and those that have 3-prong plugs. Look also for appliances that have 2-prong plugs but have ground wires sticking out from it.
Appliances with 2-prong plugs
Appliances with 2 prongs, but with a ground wire sticking out from it
Appliances with 3-prong plugs
Why do you think these appliances in the right column need to have 3 prongs in their plugs? 2. Ask your parents or elder siblings the following:
Do we have appliances that originally have 3 prongs, but we now use in 2-hole outlets? (either by using an adapter or by having the 3rd prong taken out)
Why do some appliances have ground wires? Where do we connect these ground wires?
End of DEEPEN: In this part of the lesson, you learned how to be safe from lighning, and from electric shock while using your electrical appliances. In the next part, you’ll do something that will bring you into a useful understanding of what you’ve been learning so far.
NEXT
44
TRANSFER: Your goal in this section is apply your learning to real life situations. You will interview some people who actually work with these safety devices with electricity.
3.6 Interviews: electrician or an electrical safety inspector / engineer
1. Go to a hardware store. Ask someone there about the differences between the 2-prong plugs and 3-prong plugs, and 2-hole and 3-hole outlets.
2. Go to the city or municipal safety engineers’ office. Interview an electrical
safety inspector / engineer about grounding installations at residential houses. Ask about how home builders are complying with this safety requirement.
3. If you have an electrician in your neighborhood, ask him/her to show you the
ground wiring in your house’s 3-hole outlets for some of your appliances. Inquire further on how these things keep you safe from electric shocks.
Submit a one-page double-spaced report about the results of your interview.
End of TRANSFER: In this section, your task was to really see the safety features of ground wires and the specialized plugs and outlets for some appliances. Through interviews, you should have also obtained first-hand information about these safety mechanisms. Can you already confidently answer the following questions?
What does it mean that some appliances need to be grounded?
How does a lightning rod protect us from harm? If not yet, then you may have to go back to the readings or interview another electrical safety engineer or electrician. Review your answers to the Safe-or-Unsafe questions in Activity 3.3. Review as well the correct answers. If you are still not convinced of the correct answers, and therefore you are “cognitively-at-risk” of electrical accidents, discuss this as well with an electrician or an electrical safety engineer. You have completed this lesson. Before you go to the next lesson, you have to answer the following post-assessment. If you pass this test, you may move on to the next lesson. If you do not pass this test, you may go back and review the lesson and take this test again.
NEXT
45
1. Lightning rods need to be grounded _____. A. always * B. only during the rainy seasons C. only if there are people inside the building D. only if the house’s outlets are not grounded 2. One lightning rod is enough to protect _____. A. one village B. one family inside a building C. one small structure or building * D. many buildings within a kilometer radius 3. A lightning rod is placed on the highest point in a building so that _____. A. it can gather as much charge as possible from the clouds B. it will be far away from anyone’s reach, keeping everyone safe C. lightning will most likely hit it instead of other parts of the structure * D. lightning will more likely hit other lower buildings without lightning rods 4. Which of the following is the BEST thing to do when you are outdoors and
suddenly a thunderstorm occurs? A. Open your umbrella. It will repel lightning. B. Run for the nearest shed, shelter or building. * C. Take shelter under the nearest tree and stay close to its trunk. D. Walk slowly and carefully. There’s no sense trying to outrun lightning. 5. Will an appliance with 3-prongs in its plug, still function if it is plugged into a 2-
hole outlet? (either the 3rd prong is removed or an adapter with 2 prongs is used)
A. Yes, but it poses hazards of electric shock to its users. B. Yes. It is common practice to remove the 3rd prong or use an adapter. C. No. The third prong is essential, and the appliance will not work at all.
D. No. The appliance may still work for a while, but it will stop working after some time.
6. Which of the following sets of appliances either has a ground wire or a three-
pronged plug? A. cellphone charger, electric fan, and TV B. desktop computer, DVD player, and oven toaster C. washing machine, most laptops, and electric fans D. washing machine, electric stove, and shower heater *
7. Where should ground wires (of appliances that have them) be connected? A. to the TV antenna B. to the screw that holds the wall outlet’s cover C. to the metal water pipes that go into the ground * D. to the concrete wall of the house, through an iron nail
NEXT
46
Lesson 4 Applications of charges and charging processes
In this lesson, you will:
Discuss practical and technology applications of the charging process and the interactions between charged bodies.
Investigate and report on how concepts on charges are applied in industries and in cleaning up the air.
Keep in mind this question as you start this lesson and perform the next activities:
How are these concepts on charges applied in industries and in cleaning up the air?
EXPLORE: Congratulations! You are now in Lesson 4 of this module on Electricity. In the previous section you looked at real world applications to protect you from electric charges. In this lesson, we focus on the following question: How are these concepts on charges applied in industries and in cleaning up the air?
4.1 Webpage reading: industrial application of electrostatic charging
Start this lesson by reading these web-pages. See how electrostatic charging and the interactions between charged objects are used in a variety of applications.
This web page discusses how spray-painting uses electrostatic interactions give surfaces a smooth coat of paint: http://www.gcsescience.com/pse8-electrostatic-charge-paint-spray.htm
Quite similar to the previous page, this web page discusses how electrostatic repulsion is applied in insecticide sprays: http://www.gcsescience.com/pse12-electrostatic-insecticide-spray.htm
This web page discusses how an inkjet printer applies electrostatic interactions: http://www.gcsescience.com/pse9-electrostatic-charge-inkjet-printer-nozzle.htm
Even photocopiers apply electrostatic charging and interactions! Read this page to see how: http://www.gcsescience.com/pse10-electrostatic-photocopier.htm
47
This page discusses a very relevant application of electrostatic charging and interactions for reducing pollution from chimneys: http://www.gcsescience.com/pse11-electrostatic-chimney-pollution.htmError!
Hyperlink reference not valid.
You can actually just click the right-arrow (next page) button at the bottom. Which of these applications do you appreciate most? Why? Have you heard any other applications of electrostatics and charging processes not mentioned in these pages? Search articles on these applications and share what you get to your network of online learners. Find time to read the pages shared by other learners to you. End of EXPLORE: In this first part of the last lesson, you read and learned about several applications of electrostatic charging and interactions. It’s amazing how we may have already been using these devices, yet we are not mindful, until now, of the simple science ideas behind them. In the next activities, you will simulate and investigate on the least familiar, yet very relevant and important application of electrostatic charging and interactions: the electrostatic precipitator.
NEXT
FIRM UP: Your goal in this section is to learn and understand this key concept:
Electrostatic charging is useful in cleaning up the air of pollutants from different industrial facilities
Keep this question in mind as you do the next tasks:
How are these concepts on charges applied in industries and in cleaning up the air?
48
4.2 Hands-on: Cleaning up the air using balloons How is electrostatics useful? To better appreciate the applications of electrostatic charging, do this simulation on cleaning the air using charged balloons. Open and study the web page below:
http://www.teachengineering.org/view_activity.php?url=collection/cub_/activities/cub_air/cub_air_lesson10_activity2.xml Perform the steps to simulate how a charged balloon can attract “polluting particulates” in the air. Again, it will be good if you have family or neighbors as your audience in this demonstration. Enjoy your show and the question-and-answer portion after your demonstration. How effective is your balloon air cleaner? Is it 100% efficient? Will it be useful? Explain.
NEXT DEEPEN
4.3 Web-page reading: Electrostatic precipitator
To deepen your understanding of this important application of electrostatics, read the following web pages: These web pages are nice follow-ups to your previous reading on the electrostatic precipitator: http://www.explainthatstuff.com/electrostaticsmokeprecipitators.html http://anto-hendarto.blogspot.com/2011/05/electrostatic-precipitator.html Take down notes, specially details that will help you answer these questions. Draw diagrams that demonstrate your understanding of how electrostatic charging is applied. .
How does an electrostatic precipitator work?
Why would we need these electric precipitators?
What facilities are installed with these electrostatic precipitators?
49
4.4 Electrostatic precipitator: Make a model Another way to deepen your understanding is by making another model of the technology application that you are studying. Open and study the page below: http://www.woodrow.org/teachers/chemistry/1989/12model-electrostatic.html If you can, collaborate with other online learners on how to build this model. This way you can share with the expenses and the effort in putting the model together. Also, with collaboration, you’ll have other persons to compare notes with of your understanding of the lessons so far. You may visit your school’s laboratory and use their available materials to build the model.
In your notebook, write a brief reflection on your experience of building a working model of the electrostatic precipitator. Do you think this device is worth the effort and the electricity used up for it? Why or why not?
NEXT
TRANSFER In this module’s closing lesson, your final task is to check on a nearby factory or power plant in your community, and see whether it has electrostatic precipitators installed in its chimneys. You may collaborate with up to three (3) other online learners. Your output will be a multimedia report of your investigation. Your report shall be uploaded for a panel of reviewers to evaluate and score. Your report shall include the following:
Narration of your preparations for the interviews: inquiries made, appointments set, etc.
Documentation of your investigation: Transcripts and/or recordings of interviews, videos or pictures of your visit to the facility.
Feedback to the facility administrators: Commendations if they have been very helpful and that they have been using the precipitators properly and effectively; Suggestions if the operation can still be improved; or complaints filed to government authorities if you think the facility is not using the electrostatic precipitator.
Your report should be comprehensive, and engaging, and demonstrates a methodical approach to addressing the issue.
50
Here’s a rubric by which your report shall be scored:
Criteria 4 3 2 1 Comprehensiveness of the report
Very comprehensive. Important facts and evidences were gathered. Additional information present reflects student’s deep understanding.
Comprehensive. Acceptable, but some things can still be added.
Some key information are lacking. Not quite complete.
Quite unsubstantial. “More work needs to be done.”
Engaging Very engaging. The report is worth sharing to the national news agencies.
Engaging. Good material for a local news item.
Not engaging. A number of the audience is easily disinterested.
Not engaging. Hardly anyone wants to finish the report.
Methodically addressed the issue
Very scientific and methodical. Variables are clearly defined. Data and arguments are methodically presented.Writing style is interesting and vivid.
Scientific and methodical, but the writing style and presentation can still be improved.
Shows some lapses or gaps in the methods and analysis of the issue.
Very serious gaps in the methods and analysis are present on the issue.
Before you go on to the post-assessment, go first through a review on the concepts and ideas learned from the different activities. Open the link below, and answer the questions there. http://www.gcsescience.com/pse13-electrostatic-charge-questions-answers.htm If you commit some mistakes, you are advised to return to the Lessons and the Webpage readings to clarify further your missed or incomplete understanding.
Write a 1 to 2-page reflection on your experience in the entire module. You may choose to answer one, some, or all of these guide questions:
What do you consider your most important learning in this module?
What did you find challenging yet engaging?
What did you find difficult and frustrating?
Besides the investigation on electrostatic precipitators, what other investigations related to electrostatic charges and charging could you work on later?
NEXT
51
POST-ASSESSMENT: It’s now time to evaluate your learning. Click on the letter of the answer that you think best answers the question. Your score will only appear after you answer all items. If you do well, you may move on to the next module. If your score is not at the expected level, you have to go back and take the module again.
1. The nucleus of atoms consists of _____, so its charge is ____. A. neutrons only ; neutral B. electrons and protons ; neutral C. protons and neutrons ; positive * D. neutrons, protons and electrons ; neutral
The nucleus is positive because it has protons in it. The negatively charged electrons are outside the nucleus.
2. A chlorine ion, Cl- has a net charge of -1 because ______. A. it has only one electron B. it has one less electron than protons C. it has one more electron than protons * D. it gave away one proton to another atom
A chlorine atom has 17 protons in its nucleus and 17 electrons outside. It easily gains one more electron, and so it has one more electron than protons, becoming a Cl- ion.
3. If a neutral metal sphere is placed in contact with a negatively charged metal
rod, the sphere will _____. A. remain neutral B. become positively charged C. become negatively charged as well * D. fluctuate from being positively charged and negatively charged
Some of the excess electrons in the negatively charged rod will transfer to the initially neutral sphere. This will make the initially neutral sphere also in excess of electrons and therefore positively charged.
52
4. In charging by induction, a charged body X is placed near to a neutral body Y.
If X is positively charged and Y is connected to the ground, Y will _____. A. remain neutral
B. become negatively charged C. become positively charged as well * D. fluctuate from being positively charged and negatively charged
Body X will cause electrons in body Y to move to the side near body X. With the grounding, electrons will flow into body Y, making it negatively charged.
http://www.ahsd.org/science/stroyan/APPhysics/CH15/chargi7.gif
53
5. If a negatively charged body is to be connected to the ground, then _____. A. all its electrons will go to the ground B. its excess electrons will go to the ground * C. it will take in some protons from the ground D. it will take in some electrons from the ground
Only electrons can be added or removed from bodies. A negatively charged body has excess electrons. When grounded, these excess electrons will flow to the ground until the body becomes neutral.
6. Which of the following most needs to be grounded? A. desktop computer B. electric stove * C. flat iron D. hair dryer
The metal casing of the electric stove has a
good chance of becoming electrically in contact with the live wires. Also, charge can accumulate in it. If this happens, the person using it is at risk of an electric shock. With proper grounding, usually done through the 3rd (round) prong in its plug, this risk is minimized, if not entirely eliminated.
54
7. Lightning rods are placed _____ of a building. A. at the base
B. above the windows C. above the highest point
D. on all the corners of the rooftop
Placing rods above the highest points of a building will ensure that if ever lightning strikes, it hits the lightning rod, and not any other part of the building.
8. A lightning rod works by _______. A. conducting the charge to the ground, through the building B. conducting the charge to the ground, bypassing the building * C. collecting the charge into a storage device, for use later as electricity
The charge from lightning is immediately conducted down into the ground, bypassing the building, keeping the people inside the building unharmed. If the lightning rod is not grounded, then electricity will pass through the building and the people in it will not be safe. The great amount of charge cannot be stored (yet) for later use as electricity.
9. A single electron’s charge is – 1.6 x 10-19 Coulomb. What will be the charge of a body if it loses 1 billion of its free electrons?
A. 1 x 109 Coulomb B. + 1.6 x 10-9 Coulomb C. + 1.6 x 10-10 Coulomb D. - 1.6 X 10-10 Coulomb
Q = n qe where Q is the charge developed n is the number of electrons qe is the charge of an electron
Q = n qe = (– 1.6 x 10-19 Coulomb per electon) x (1 x 109 electrons)
= – 1.6 x 10-10 Coulomb
However, since the body loses electrons, its charge is positive: + 1.6 x 10-
10 Coulomb.
55
For items 10 and 11, refer to the triboelectric series in the box at the right:
10. If a glass rod is rubbed with Styrofoam, what will
be the sign of their charges? A. glass rod: positive; Styrofoam : negative * B. glass rod: negative; Styrofoam: positive C. both will have positive charges D. both will have negative charges
The Styrofoam will gain electrons from the glass rod. 11. Which rubbing material will create the most charge
on a rubber stick? A. fur B. human hair * C. silk D. wool
The more electrons gained by the rubber stick, the greater the charge created in it. From among the choices, human hair is highest in the series, farthest away from rubber. It has the least tendency to gain electrons, or conversely, it will most easily give its electrons to the rubber stick.
12. The picture at the right shows a green wire attached to the motor at the underside of a washing machine’s wash tub. What is this wire and what is it for?
A. It is the power line. Without it the machine will not run.
B. It is the line to the buzzer alarm. Without it the user won’t hear an alarm even when it is done washing.
C. It is the grounding wire. It discharges the motor and the whole machine.
D. It is an “anti-theft” wire. With it attached to the main circuitry, the washing machine will not be stolen, as the thief will be electrocuted.
The green wire is a grounding wire. Its other end should be connected to the water pipe outside the machine. This way, charge is prevented from building up in the washing machine.
leather glass
human hair wool fur silk
rubber styrofoam
polyvinylchloride (PVC)
Increasing tendency to gain electrons
56
13. What could happen if this wire is not firmly connected at either ends?
A. The motor for the wash tub will run, but that for the spin dryer will not. B. The washing machine will not run. C. The motor will keep running even as the timer goes down to zero. D. The person using the machine might get an electric shock. *
If the grounding wire is not connected, then the charge that may accumulate in the machine may cause an electric shock on the person using it.
14. Which of the following will be the BEST thing to do when you are in your car, on a long trip on an open plain highway, and a thunderstorm suddenly starts?
A. Get out of your car and take shelter under the nearest tree you can find.
B. Stay in your car and take a stop in the next stable shelter or gas station. *
C. Stay in your car, but stop at the roadside and wait for the storm to be over.
D. Stay in your car, but turn off the radio and lights, as using these increases the risk of lightning hitting your car.
People in open fields (with no trees or houses) are at risk of getting struck by lightning. The other risks above should also be avoided, but the most fatal of them is the first.
57
15. Pictured below is the process by which an electrostatic precipitator reduces the pollutants releases to the atmosphere by factories. Which statement below best summarizes the process?
A. Some smoke particles attach themselves to the metal grid, and the others that pass will stick to the collecting plates.
B. Smoke particles acquire a charge opposite that of the metal grid, and then they get attracted to the similarly charged collecting plate.
C. Smoke particles acquire a charge similar to that of the metal grid, and then they get attracted to the oppositely charged collecting plate. *
D. The metal grid gives the smoke particles either positive or negative charges. Positively charged smoke particles will attach to the negative collector plate, while the negatively charged smoke particles will attach to the positive plate.
If the grid is positively charged, the smoke particles will become positively charged. To attract the charged smoke particles, the collecting plates will have to be negatively charged. If the grid is negatively charged, the smoke particles will become negatively charged. To attract the charged smoke particles, the collecting plates will now have to be positively charged.
Collecting
plates
Metal grid
Smoke particles
become
charged
58
16. You conducted a “magic show” with the kids in an orphanage you visited. You showed them the demonstration where tissue bits flew up to the plastic sheet. Assume the plastic sheet to be negatively charged. What was the charge of the tissue bits?
A. They are neutral; the upper side is positive and the lower side is negative. *
B. They are neutral; the upper side is negative and the lower side is positive.
C. Positively charged. How else could they be attracted to the plastic sheet?
D. Negatively charged. The plastic sheet is actually positively charged, not negative.
The negatively charged plastic sheet repels the electrons in the tissue bits, pushing them lower. This polarizes the tissue bits, with the upper side positively charged, and the lower side negatively charged. The tissue bits however are still electrically neutral. (Left figure below) With the tissue bits now polarized, the upper side gets attracted to the plastic sheet. The attraction overcomes the repulsion that the lower side experiences. (Right figure below)
Table top
Plastic
sheet
- - -
-
-
+ + + + +
- -
- -
- -
- -
-
+
- -
- -
- -
- -
59
17. You then touched the top side of the plastic sheet where there are tissue bits under it. The tissue bits under the touched spot fell back to the table. Why?
A. The finger changed the plastic’s
charge to positive, and it then repelled the tissue bits.
B. The finger discharged the plastic, which then was not able to attract the tissue bits any longer. *
C. The finger is positively charged so it repelled the tissue bits.
D. Tissue is always repelled by the human body.
Touching the plastic sheet grounds the plastic, at least the point touched. This point becomes neutral, and so no longer able to attract the tissue bit. Option B is not possible, as your hand is connected to your body, and is connected to the ground. The small plastic sheet can polarize a smaller object, but not a bigger body that is connected to the ground. Option D is not possible. There is no way for the finger to cause the plastic sheet to have a positive charge. The finger can take away just enough electrons to make it neutral, but not to make it positively charged.
Table top
Plastic sheet
60
18. You took a summer job in a hardware store. One customer approached you and asked, “What is the third hole in these outlets for? Should I buy these for my entire house?” Which of the following will be your BEST reply?
A. “It’s for your safety. Yes, it will be good if all outlets in your house have 3 holes.”
B. “The third hole is for appliances that need to be grounded, like washing machines and shower heaters.” *
C. “It’s there to accommodate appliances with three pronged plugs. It is ok to just have 2-hole outlets. For 3-pronged plugs, there are available adapters…”
D. “The third hole is for a more stable fit, so the plug won’t easily fall off. This is best for appliance with moving parts, like electric fans and washing machines…”
Appliances with heating elements (stove, oven, washing machines, shower heater) are prone to accumulating charges that may cause electric shock. The third prong actually connects to a grounding wire inside the round hole in the 3-hole outlet. Most other appliances do not need grounding, and so they only have 2-prong plugs and will need just 2-hole outlets. (Thus, A is not really a good answer.) Remember, it is not just a matter of having a 3rd hole for the 3rd prong. The grounding wire inside the third hole is the key protective device against shocks. Thus, Option B is dangerous if you have ungrounded 3rd holes in outlets in your living room. Plugging in your stove there will not ground your stove. Option C is not good, as plugging in 3-prong devices into 2-hole outlets through an adapter does not ground the appliance.
2-hole outlet
3-hole outlet
61
19. If you happen to pass by this road in the picture, what will you tell the girl who is flying her kite?
A. “Be careful. Don’t fly it higher than the cables.” B. “Be careful. Better flying that higher above the cables.” C. “Hey! Fly that on an open field, away from any power lines!” *
D. “Flying kites under power lines is ok as long as the string doesn’t touch them.”
Cartoon from: http://www.alliantenergykids.com/FunandGames/OnlineGames/007006
20. Examine the picture at the right. If you are a
safety inspector, what will you tell the people in this house? List 3 things that you will tell these people.
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
Cartoon from: http://www.alliantenergykids.com/FunandGames/OnlineGames/007005
62
Do not use electrical appliances when on or near water. Do not stick anything into oven toasters and other electrical appliances, especially when they are plugged in. Have safety covers on electrical outlets. Do not leave small children unattended.
NEXT
GLOSSARY: 1. Electrostatics: The branch of physics concerned about charges that are not in
motion as in currents in wires. 2. Conduction: the charging process by which metallic objects pass among
them electrons, therefore causing both metals to acquire same-sign charges. 3. Induction: the charging process by which non-metallic objects can be
charged even while the charging body does not give up to, or take in electrons from, the body being charged.
4. Grounding: the process by which things are made electrically neutral, either
by providing it with electrons (the number by which it is deficient) from the ground, or by taking away its excess electrons.
5. Polarization: the process by which a neutral object is made to have positive
and negatively charged poles, due to a charged body brought near it. 6. Electroscope: a device that is useful in detecting the presence of charges in
bodies; this device is also useful in demonstrating the different charging processes.
7. Triboelectric series: a listing of materials according to their capacity to take in
electrons when rubbed with other materials. 8. Electrostatic precipitator: a device installed in chimneys, by which smoke and
exhaust is being cleaned up of the harmful particles; a feature application of electrostatics and electrostatic charging
63
WEBSITE RESOURCES AND LINKS IN THIS MODULE:
Lesson No. Activity / Assessment / Short description
Website link
1.2 Charges in the atomic level
http://web.jjay.cuny.edu/~acarpi/NSC/3-atoms.htm
1.2 On electrons
http://www.windows2universe.org/physical_science/physics/atom_particle/electron.html
1.2 On protons
http://www.windows2universe.org/physical_science/physics/atom_particle/proton.html
1.6 Charging by Friction
http://regentsprep.org/Regents/physics/phys03/atribo/default.htm
1.8 Video: Straw electrostatics
http://www.youtube.com/watch?v=Ne7oqESE5Zw
2.1 Video: Charging spheres by induction
http://www.youtube.com/watch?v=J2g8g7tr-1Y&feature=endscreen&NR=1
2.1 Video for assessment: Electroscope induction with grounding
http://www.youtube.com/watch?v=-iykzxpnpjk&feature=endscreen&NR=1
2.1 Electrostatic charge: Attraction and repulsion
http://www.gcsescience.com/pse3-electrostatic-charge-attraction-repulsion.htm
2.2 Charging balloons interactive simulation
http://phet.colorado.edu/en/simulation/balloons
2.3 Electroscope text and diagram
http://www.gcsescience.com/pse4-electrostatic-gold-leaf-electroscope.htm
2.3 http://www.youtube.com/watch?v=2PmWlPjV6n0&feature=fvwrel
64
Video: Making an electroscope
2.4 Make your own electroscope
http://www.youtube.com/watch?v=jBF-144bV18&feature=related
2.5 Video: Electroscope charging explained
http://www.youtube.com/watch?feature=endscreen&NR=1&v=-JsVZwc1dOo
2.7 How neutral objects get attracted to charged objects
http://www.gcsescience.com/pse5-electrostatic-charge-neutral-attract.htm
2.7 Charging processes: Conduction and induction
http://www.studyphysics.ca/30/charging.pdf http://www.physicsclassroom.com/class/estatics/U8L2b.cfm http://www.physicsclassroom.com/class/estatics/U8L2c.cfm
2.9 Worksheet: Conduction and induction
http://dev.physicslab.org/Document.aspx?doctype=5&filename=Compilations_CPworkbook_ElectrostaticsConductionInduction.xml
2.9 Worksheet: Charging by inductions
Worksheet: 3-ele-01_charging_by_induction.doc
2.10 Polar molecules
http://www.gcsescience.com/pse5-electrostatic-charge-neutral-attract.htm
2.10 Water as a polar molecule and universal solvent
http://www.edinformatics.com/interactive_molecules/water.htm
2.11 Video: Jumping and floating beads (into to grounding)
http://www.youtube.com/watch?v=7LxyA-7KIoo
3.1 http://www.gcsescience.com/pse6-electrostatic-charge-shock-spark-danger.htm
65
Intro to lightning: Electrostatic shock
3.1 Lightning facts from National Geographic
http://environment.nationalgeographic.com/environment/natural-disasters/lightning-profile/
3.2 Lightning interactive animation
http://environment.nationalgeographic.com/environment/natural-disasters/lightning-interactive/
3.3 Lightning safety tips
http://environment.nationalgeographic.com/environment/natural-disasters/lightning-safety-tips/
3.3 More on safety from lightning: Lightning protection institute
http://www.lightning.org/faq?tid=86
3.3 More on lightning rods at home
http://www.ehow.com/how-does_4588127_lightning-rod-protect-house.html
3.4 2-pronged and 3-pronged plugs in appliances
http://electronics.howstuffworks.com/everyday-tech/question110.htm
3.4 The ground wire and 3-hole outlets
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/bregnd.html
4.1 Uses and applications of electrostatics
http://www.gcsescience.com/pse8-electrostatic-charge-paint-spray.htm
4.2 Simple demo of precipitator using balloons
http://www.teachengineering.org/view_activity.php?url=collection/cub_/activities/cub_air/cub_air_lesson10_activity2.xml
4.3 http://anto-hendarto.blogspot.com/2011/05/electrostatic-precipitator.html
66
Web-page: Electrostatic precipitator
http://www.explainthatstuff.com/electrostaticsmokeprecipitators.html
4.4 Electrostatic precipitator: Make a model
http://www.woodrow.org/teachers/chemistry/1989/12model-electrostatic.html
4.4 Closing quiz, final check-up before the Post-assessment
http://www.gcsescience.com/pse13-electrostatic-charge-questions-answers.htm