Key TermsKey TermsUse the spaces below to define the key terms in your own words.Use the spaces below to define the key terms in your own words.

2.1Key Terms Textbook Definition Drawing / In my own words

Insulator

Superconductor

Conductor

Resistor

Resistance

ohm

Variable resistance

rheostat

2.2Key Terms Textbook Definition Drawing / In my own words

Ohm’s Law

Voltage drop

Millivoltmeter

Ammeter

Galvanometer

multimeter

2.3Key Terms Textbook Definition Drawing / In my own words

Schematic diagram

Series circuit

Parallel circuit

transistor

microcircuit

Integrated circuit

CCHAPTERHAPTER 2 – T 2 – TECHNOLOGIESECHNOLOGIES CANCAN BEBE USEDUSED TOTO TRANSFERTRANSFER ANDAND CONTROLCONTROL ELECTRICALELECTRICAL ENERGYENERGY

2.1 – C2.1 – CONTROLLINGONTROLLING THETHE F FLOWLOW OFOF E ELECTRICALLECTRICAL C CURRENTURRENT

A Unique Circuit

Neon signs usually consist as a glass tube, twisted into shape. The tube is the filled with gas and metal terminals are sealed at the ends. The metal terminals of the tube are then connected to the __________ and

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____________ terminals of the ______________. The sign is a _________, unlike the wire circuit that you saw earlier; this circuit includes a _____ as the_____________________.

Usually neon gas is a _________________ – it does not ____________________. But when __________ is applied to the tube, _________________ in the neon atoms are ____________ by the added energy, and free themselves from the atoms. The ______________ electrons leave behind the positive neon ions which creates a mixture that is excellent at _________________ current. As the current continues to add energy to the neon gas, some of the electrons fall back into the neon ions releasing their energy as the ________ that we see.

Circuit Video http://www.youtube.com/watch?v=-Rot9uaVO8s

Conductors and Insulators

Electrons in insulators are ____________ bound to the ___________ nucleus of their atoms. They _____ moving away from the nucleus. In conductors, the electrons are not as tightly bound. They are _____ to move. However, a current will only flow when the conductor is connected to an __________________. The electrons move toward the positive end of the voltage source. Therefore, we say that electrons move when _______________ is applied.

http://www.youtube.com/watch?v=EAZVs8Mkowk

Superconductors

Metals such as silver, copper, mercury, and gold are all excellent _________________, but they are not _____________ conductors. When electrons travel through these substances, they encounter some _____________________. The amount of resistance varies from metal, which makes the choice of one metal over another as being a better conductor. However it is possible for metals to ________________. Superconductors are __________ conductors – they have no ______________ to electron flow.

Using Conductors, Resistors, and Insulators

In some applications, a type of __________ called a ______________ is useful. A resister allows ________ current to pass, but provides ______________ to it.

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This limits the amount of current. For any given voltage, more current flows through a resistor with a low resistance than through one with a high resistance. ________________ is a measure of how difficult it is for _________________ to flow through a substance. It is measured in ______ . The symbol for ohm is Ω, the Greek letter omega.

The more resistance a substance has, the more the substance _____________ from each electron that passes through it. The energy that is gained by the substance is radiated to its surroundings as either _____ or ________. Examples of this are an incandescent bulb and the element in a heater both radiate heat and light because of _______________.

Solutions can also be ______________. The more charged particles in a solution, the better it ______________. Distilled water is not a good conductor because it only contains water molecules. These molecules have no _____________. However, tap water and water in the environment are conductors because they contain many dissolved minerals. Knowing the conductivity of a particular substance can be of great use. For example, you could use a conductivity apparatus to check the purity of a substance.

The polygraph or “lie detector” is another application of resistance. It measures skin resistance, blood pressure, and respiration. All of these factors change under stress. Sweat is mostly a salty solution so it contributes to the change in skin resistance. To measure the change, two or more metal ________________ are attached to the skin. Therefore, a person who is lying is probably under the most stress. The lie causes an ______________ in _________________ between

the electrodes. This would show up as a peak on the graph.

Switches and Variable Resistors

A __________ is used to turn electricity ___________ in a circuit. When a switch is on, two conductors are pressed together so that current can ______ from one to the other. When the switch is off, the conductors are separated and no current flows. Sometimes you want to change the current flow gradually in a circuit, rather than just turning it on or off, for example, a light dimmer in your house. This type of control device is called a ________________________ or __________________.

Rheostats can _________________ or _________________ the amount of current in a circuit by adjusting the portion of the resistor that the current travels through. Examples include: volume controls on stereos and foot operated speed controls for sewing machines.

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Check and Reflect p. 303

1. What is the difference between a conductor and an insulator?

2. What is a resistor?

3. How does a switch control current flow?

5. Why do some substances conduct while others do not?

6. Use a labelled diagram to explain how electrons behave I a conductor when:a. No voltage is appliedb. Voltage is applies

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9. You have built a fountain for you backyard pond. How might your control the pump speed so that the water doesn’t spray too high or too low?

2.2Modelling and Measuring Electricity

Modelling Voltage

The flow of water is very similar to the flow of voltage. Unless there is a __________ in elevation, water doesn’t flow – it simply sits in a pool. If you pump water up a hill, it gains gravitational potential energy, and then flows back down. In a similar way, a cell, battery, or generator _________ electrons to a point with a higher ________________________. Electricity will not flow without a ____________________ in electrical potential, just as water does not flow without a difference in gravitational potential energy.

Modelling Resistance and Current

The flow of water in pipes is another useful model of electricity. For example, if you were using a reservoir to provide irrigation water for a field, you need to decide what size pipes to use to drain the reservoir. A pipe with a small diameter might be easier to hook up. However, the

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__________ and __________ the pipe is, the more resistance is has to the flow of water. A pipe with a ____________ diameter has less resistance, which allows a greater flow of water. Similarly, the amount of resistance in a circuit affects the electrical current. For any given voltage, current ______________ if you add resistance. As with water flow, you get the _______ resistance with a short, wide path with no ___________________. The shorter and thicker the wire, the less resistance it creates for electrons. The flow of current will be _____________ if it has to pass through a _____________.

Ohm’s Law

German scientist Georg Simon Ohm made an exciting electrical discovery in the early 1800’s. He was able to prove a link between _____________, ___________, and ______________________. The unit of resistance, the ohm, was named in his honour. Ohm’s Law states that as long as temperature stats the same

1. The resistance of a conductor stays constant, and2. The current is directly proportional to the voltage applied

In other words, if you ____________ the voltage in a circuit, the current also _______________. Ohm’s law also covers changes in resistance. If the voltage stays the same, but a resistor of greater value is used, then the current decreases. This table shows how to use Ohm’s Law

Applying Ohm’s Law

Example: An electric stove is connected to a 240-V outlet. If the current flowing through the stove is 20 A. What is the resistance of the heating element?

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Skill Practice

1. A 30-V battery creates a current through a 15-Ω resistor. How much current is created?

2. A motor has an internal resistance of 40 Ω. The motor is in a circuit with a current of 4.0 A. What is the voltage?

3. A current of 625 mA runs through a bulb that is connected to 120 V. What is the resistance of the bulb?

Voltmeter: The voltage is the ____________________ between two points. To measure the potential difference across a cell, battery, or other device in a circuit, each terminal of the device must be connected to the appropriate positive or negative terminal of a voltmeter. The potential difference across a resistor is known as a ______________________. Meters used to measure small voltages are sometimes called _____________________.

AmmetersAmmeters are used to measure electric ____________ in amperes. Current is the rate of flow of electricity in a circuit. It is the measure of how many ______________ move past a point in a circuit each second. To measure this flow, an ammeter must be placed so that current flows through it. If a circuit consists of only one continuous loop, you can insert the ammeter between

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any two circuits. The current will be the same at any two points along the circuit. Meters used to measure small currents are sometimes called galvanometers.

MultimetersMeters made with several different measuring circuits mounted in the same case is called a multimeter. It has the ability to measure voltage, current, or resistance in a circuit. You must be careful to select the right setting for the quantity you want to measure.

Types of Resistors

There are a wide variety of resistors that are made for different applications, especially in electronics. For examples, radios, and televisions contain dozens of different resistors. Resistors are available with values covering the whole range between conductors (very low resistance) and insulators (very high resistance). The two most common types of resistors are ________________ and

______________________. Wire wound resistors are available from 0.1Ω up to 200 kΩ. The longer and thinner the wire, the __________ the resistance. Carbon-composition resistors are made of carbon mixed with other materials. By varying size and composition, resistors can be produced from 10Ω to 20 MΩ

Check and Reflect p.310

1. How is current related to voltage in a circuit?

2. How is current related to resistance in a circuit?

4. What does the term “voltage drop” mean?

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5. A bulb of 15-Ω resistance is in a circuit powered y a 3-V battery.a. What is the current in this circuit?

b. What would the current be if you changed to a 45-Ω bulb?

6. A digital recorder plugged into a 120-V outlet has an operating resistance of 10000 Ω. How much current flows in this device?

7. An electric heater draws 10 A from a 120-V source. What is the heaters resistance?

8. A current of 1.5 A flows through a 30-Ω resistor that is connected across a battery. What is the battery’s voltage?

2.3 Analyzing and Building Electrical Circuits

Circuit Drawings

Engineers and people who design electrical circuits use special symbols that show the components and connections clearly. This makes it easier to plan and analyze a circuit

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before you build it. A drawing made of these symbols is often called a _____________ or ___________________.

Parts of a circuit – Schematics can sometimes seem complicated, but all circuits have four basic parts: 1. ________________________2. ________________________3. ________________________4. ________________________

1. A source provides energy and a supply of electrons for the circuit2. A conductor provides a path for current3. A switching mechanism controls current flow, turning it on and off, or directing it into different

parts of the circuit4. A load converts electrical energy into some other form of energy

Schematic diagrams can make it much easier to understand where the current flows and how the device functions.

Series Circuits

The circuit in which current passes through each bulb in turn is called a _____________ . In a series circuit, there is only ____ pathway for the

current to take. If the pathway is interrupted, the circuit ____________

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function. Another problem with series circuits is that the ______ loads in the circuit, the more _____________ in the circuit which in turns ____________ the current. For example, adding another bulb to a string of lights makes all the lights dimmer. There are benefits such as wiring in a house to plugs or lights. This makes it possible to turn off the electricity in the circuit with on switch.

Parallel Circuits

Parallel Circuits have a ________________ current path for each section of the circuit. In a parallel-wired string of lights, each bulb has its _______ path to the current source. An ___________________ or break in one pathway does not affect the rest of the pathways in the circuit. Also, adding a ____ pathway with more resistors does not affect the resistant in any of the other pathways.

Applications of Series and Parallel Circuits

House Wiring is one of many applications that use ___________ circuits. You would not want your refrigerator to go off if a bulb burnt out. This could happen if you wired your lights and wall sockets in ___________ instead of in ____________. If you want to control more than one device in your

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house with one switch, you would connect the switch in series with the ___________ ______________.

A switch in one branch of a parallel circuit controls only the devices in that branch. But a switch in series with all the branches controls all of them. Switches are important in series because sometimes it is necessary to turn off the electricity in part or the entire home.

Conventional switches are practical and convenient for a home. But for the tiny circuits in advanced electronics, ______________ must be used instead. Transistors are often referred to a ___________ components because they are made of a solid material with no moving parts. Transistors can act as _____________ . Microcircuits also called ______________ circuits and are made up of microscopic _____________and _______________. A microcircuit is a circuit on an extremely small scale. The latest microcircuits contain more than a million components in a square centim

Check and Reflect p. 316

1. What are the two types of electrical circuits? Draw a diagram of each type. Use the same components in each diagram.

2. What is a schematic? Illustrate the schematic symbols for a lamp, switch, rheostat, motor, fuse, and ammeter.

3. What is the difference between a cell and a battery in a schematic diagram?

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4. How does resistance change as you add bulbs to a series circuit? Explain.

7. Is the wiring in your home likely to have series of parallel circuits? Explain

9. Why are motors, lamps, and other resistors considered “loads” in electrical circuits?

10. You have been asked to design a toy that looks like a dancing chicken. The toy must have an on/off switch and a motor that operates whenever a light shines on the toy. Draw a schematic for the toy.

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