APPLICATIONS OF SEMICONDUCTING MATERIALS

Karen Porter-Davis

Chamblee Charter High School

CLASS LEVEL High School Advanced/Honors/Gifted Physics /AP Physics

LESSON TIME

3 to 4 days (with extended activities)

PROBLEM What are semiconductors and why are they important for integrated circuits in

microelectronics?

ABSTRACT Semiconductors are solid crystalline substances that tend to have greater electrical

conductivity than insulators, but less than good conductors. The valence band of a

semiconductor is full similarly to that of an insulator, but the band gap is much smaller

(about 1 eV compared to about 5 eV). In fact, the band gap in several semiconductors is

so small that electrons are easily able to be thermally excited into the conduction band.

This means that the electrical conductivity of many semiconductors is strongly reliant on

temperature. Even though conductivity is not dependent only on the number of free

electrons, materials with less than one free electron per million atoms will not easily be

able to conduct electricity. To have practical uses for semiconductors the conductivity

must be greatly increased and raising the temperature is not a very reliable way to

achieve this goal. However, it is accomplished by doping (adding a very small amount of

other atoms in with the semiconductor), which increases conductivity by adding either

electrons or holes to a semiconductor.

By putting together n-doped and p-doped semiconductors diodes and transistors can be

created. In these devices, voltage and current can be varied in more complicated way

than directed by Ohm’s Law. To build a practical circuit it is important to have switches

(on/off switches are related to binary code) that can control current, voltage, and

resistance. Semiconductors can easily be manipulated to become conducting or insulating

materials and can change their conductive properties very quickly. This allows for the

possibility of building millions of tiny semiconducting “switches” on a single chip.

NATIONAL STANDARDS ALLIGNMENT

CONTENT STANDARD A: UNIFYING CONCEPTS AND PROCESSES

• Systems, order, and organization.

• Evidence, models, and explanation.

• Change, constancy, and measurement.

• Evolution and equilibrium.

• Form and function.

CONTENT STANDARD B: SCIENCE AS INQUIRY

• Understanding of scientific concepts.

• An appreciation of "how we know" what we know in science.

• Understanding of the nature of science.

• Skills necessary to become independent inquirers about the natural world.

• The dispositions to use the skills, abilities, and attitudes associated with science.

CONTENT STANDARD C: PHYSICAL SCIENCE

• Structures of atoms.

• Structure and properties of matter.

• Interactions of energy and matter.

CONTENT STANDARD E: SCIENCE AND TECHNOLOGY

• Abilities of technological design

• Understandings about science and technology

CONTENT STANDARD F: SCIENCE IN PERSONAL AND SOCIAL

PERSPECTIVES

• Science and technology in local, national, and global challenges

CONTENT STANDARD G: HISTORY AND NATURE OF SCIENCE

• Science as a human endeavor.

• Nature of scientific knowledge.

• Historical perspectives.

GEORGIA PERFORMANC STANDARDS ALLIGNMENT

SCSh1. Students will evaluate the importance of curiosity, honesty, openness, and

skepticism in science.

SCSh2. Students will use standard safety practices for all classroom laboratory and

field investigations.

SCSh3. Students will identify and investigate problems scientifically.

SCSh4. Students will use tools and instruments for observing, measuring, and

manipulating scientific equipment and materials.

SCSh5. Students will demonstrate the computation and estimation skills necessary

for analyzing data and developing reasonable scientific explanations.

SCSh6. Students will communicate scientific investigations and information clearly.

SCSh7. Students will analyze how scientific knowledge is developed.

SCSh8. Students will understand important features of the process of scientific

inquiry.

SCSh9. Students will enhance reading in all curriculum areas.

SP5. Students will evaluate relationships between electrical and magnetic forces.

a. Describe the transformation of mechanical energy into electrical energy

and the transmission of electrical energy.

b. Determine the relationship among potential difference, current, and

resistance in a direct current circuit.

OBJECTIVES

• To understand the unique properties of semiconductors and why they work

well in electronics. • To understand how diodes and transistors work in electronics. • To understand the future direction of semiconductor technology.

ANTICIPATED LEARNER OUTCOMES

a. Students should be able to describe and demonstrate how electrons and holes

move throughout a semiconductor.

b. Students should understand and demonstrate the idea of “doping” a

semiconducting material and the difference between p and n doping.

c. Students should understand how diodes are formed and their applications.

d. Students should demonstrate how LEDs work in a series and parallel circuit.

e. Students should be able to describe the uses and importance of transistors in

our modern world.

BACKGROUND

Atoms consist of a dense, positively charged nucleus surrounded by a cloud of negatively

charged electrons. The electron in an atom can possess only certain amounts of energy

(quantized). Due to this, electrons can occupy only certain allowed energy levels.

Usually the electrons in an atom occupy the lowest possible energy levels available to

them. This condition is referred to as the ground state. An atom can sometimes absorb

outside energy, which if the energy is sufficient enough, one of the atom’s electrons can

move to a higher energy level. The atom is then in its excited state. The electron may

absorb so much energy that it is no longer bound to the atom and is now free.

When identical atoms are far apart they have the same energy levels and wave functions,

but as the atoms are brought closer together, their wave functions overlap. Because no

two electrons in the same system can occupy the same state, the energy level in an atom

is altered by the influence of the electric field of another atom. This causes energy levels

to split. Adding a few more nearby atoms causes further splitting and when many atoms

interact, the energy levels are so closely spaced that they can be represented as energy

bands. The bands are separated by values of energy that no electron can possess. These

energies are called forbidden gaps. For atoms in the ground state, the lower energy

levels are completely full. The outermost band that holds electrons is called the valence

band. The lowest band that is not filled to capacity with electrons is called the

conduction band. Electrical conduction in solids explained in terms of these energy

bands and forbidden gaps is called the band theory of solids. This band theory explains

why solids fall into three categories: conductors, insulators, and semiconductors.

Conductors: When a potential difference is placed across a substance, the resulting

electric field exerts a net force on the electron. The electron then accelerates and gains

energy (the field does work on the electrons). If there are bands with in the material that

are only partially filled, then there are energy levels available that are only slightly higher

than the electron’s present level. Therefore, the electron can move from one atom to the

next in what is referred to as the conduction band. Such movement of electrons from

one atom to the next is called electric current, and the entire process is known as

electrical conduction. Materials with partially filled bands conduct electric current easily

and are considered conductors.

The electrons move rapidly and randomly (106 m/s) in a conductor due to collisions with

the cores of the atoms. However, if an electric field created by a potential difference is

applied there will be a net force pushing the electrons in one direction. Although their

motion is not greatly affected, they have a slow overall movement directed by the field

called drift velocity (10-5

m/s or slower). If temperature is increased, the speeds of the

electrons also increase which causes them to collide more frequently with the atomic

cores. Therefore, as the temperature increases, the conductivity of metals decreases

because the drift velocity decreases. As conductivity is reduced, a material’s resistance

rises.

Insulators: In an insulating material the valence band is filled to capacity and the

conduction band is empty. In these materials the valence band and the conduction band

are separated by a forbidden gap. For an electron to move from the valence band to the

conduction band it must gain a large amount of energy (5-10 eV). Though electrons

possess some kinetic energy due to their thermal energy, the average kinetic energy of

electrons at room temperature is not enough for them to jump the forbidden gap. Even

with a small electric field, almost no electrons gain enough energy to reach the

conduction band, so there is no current.

Semiconductors: Semiconductors have a smaller forbidden gap than insulators and

therefore need less energy for their electrons to jump into the conduction band. Some

electrons reach the conduction band on their own as a result of their thermal kinetic

energy and even more make it when an electric field is applied to the material. Unlike

metals, as the temperature increases the electron movement and conductivity increases.

An atom from which an electron has broken free from its valence band is missing an

electron is said to contain a hole. A hole is an empty energy level in the valence band.

The atom now has a net positive charge. If an electron breaks free from another atom, it

can land on the hole and become bound to an atom once again. When the hole and a free

electron recombine, their opposite charges cancel each other. The electron, however, has

left behind another hole on its previous atom. The negatively charged, free electrons

move in one direction and the positively charged holes move in the opposite direction.

Pure semiconductors that conduct as a result of thermally freed electrons and holes are

called intrinsic semiconductors. Because so few electrons or holes are available to carry

charge, conduction in intrinsic semiconductors is very small; thus, their resistance is very

high. (Figure below: modernworldview.net/energy/im2.gif)

Conductivity does not just depend on the number of free electrons; however materials

with less than one free electron per million atoms will not conduct electricity very well.

To practically use semiconductors their conductivity must be immensely increased. This

is accomplished by adding a small amount of other atoms (impurities) to the

semiconductor (extrinsic semiconductor). These impurities are referred to as dopants,

and will increase conductivity by either adding electrons or holes to a semiconductor.

There are two types of extrinsic semiconductors:

n-type semiconductors: This type conducts by means of adding electrons. Silicon and

germanium each have four valence electrons, if a dopant with more than 4 valence

electrons (ex. Arsenic – 5 valence electrons) is added four out of the five electrons will

bind to a neighboring silicon (or germanium) atom to fill its valence band. The fifth

electron is not needed in bonding and so can move relatively freely. This is called the

donor electron. The energy of this donor electron is so close to the conduction band that

thermal energy can easily remove it from the impure atom and place it into this

conduction band.

p-type semiconductors: This type conducts by means of adding holes. In this case,

instead of adding a dopant with more than 4 valence electrons, one with less than 4 is

added. For example, a gallium atom only has three valence electrons. If a gallium atom

replaces a silicon atom, one binding electron is missing. The gallium atom is called an

electron acceptor. This is because the gallium atom creates a hole in the silicon (or

germanium) semiconductor. Only thermal energy is needed to excite electrons from the

valence band into this hole creating a hole on a silicon atom that is free to move through

the crystal. Conduction is the result of the motion of positively charge holes in the

valence band.

Remember: both types of extrinsic semiconductors are electrically neutral. Adding

dopant atoms of either type does not add any net charge to a semiconductor. If there are

free electrons, then there is the same number of positively charged atoms. When a

semiconductor conducts current by means of holes, there are a corresponding number of

negatively charged atoms.

ELECTRONIC DEVICES

Diodes: The simplest semiconductor device is the diode. It is a device that allows

electric current to pass more easily in one direction than in the other. A diode consists of

joined regions of p-type and n-type semiconductors. Instead of two separated pieces of

doped silicon being joined, a single sample of intrinsic silicon is treated first with a p-

dopant, then with an n-dopant. Metal contacts are coated on each region so that wires can

be attached. The boundary between the p-type and n-type regions is called the junction.

The holes and electrons in the p- and n-regions are affected by the junction. There are

forces on the free-charge carriers (electrons and holes) in the two regions near the

junction. The free electrons on the n-side are attracted to the positive holes on the p-side.

The electrons readily move into the p-side and recombine with the holes. Holes from the

p-side similarly move into the n-side, where they recombine with electrons. As a result

of this flow, the n-side has a net positive charge, and the p-side has a net negative charge.

These charges produce forces in the opposite direction that stop further movement of

charge carriers. The region around the junction is left with neither holes nor free

electrons and is called the depletion layer. Because it has no charge carriers, it is a poor

conductor of electricity. Thus, a junction diode consists of relatively good conductors at

the ends that surround a poor conductor.

Forward Biased

If a battery is applied to the p-n junction so that the positive side of the battery is

connected to the p-type side and the negative side of the battery is connected to the n-type

the following occurs:

Figure: http://hyperphysics.phy-astr.gsu.edu/hbase/solids/diod.html

When the battery voltage exceeds the junction voltage (0.6V for silicon) the p-type

material is positive and the n-type material is negative. The excessive electrons now in

the n-type material are attracted across the depletion layer to the positive p-type material

with its excessive number of holes. As a result current flows and the junction is said to be

forward biased. As current flows the junction has low resistance.

Reverse Biased

If a battery is applied to the p-n junction so that the positive side of the battery is

connected to the n-type side and the negative side of the battery is connected to the p-type

the following occurs

Figure: http://hyperphysics.phy-astr.gsu.edu/hbase/solids/diod.html

Figure: http://www.ibiblio.org/obp/electricCircuits/Semi/03251.png

The negative connection of the battery has the effect attracting the holes in the p-type

material away from the material and the positive side of the battery has the effect of

attracting the electrons in the n-type material away from the material. As a result the

depletion layer increases making the insulating effect bigger. This stops a flow of

current across the junction. As no current flows the junction has high resistance. It

should be noted that a small leakage current does occur from the few minority charge

carriers, but this is very small.

In general, diodes tend to permit current flow in one direction, but tend to inhibit current

flow in the opposite direction. The graph below shows how current can depend upon

voltage for a diode. (Figure: http://www.ibiblio.org/obp/electricCircuits/Semi/03253.png)

Note the following.

• When the voltage across the diode is positive, a lot of current can flow once

the voltage becomes large enough.

• When the voltage across the diode is negative, virtually no current flows.

When reverse-biased, an ideal diode would block all current. A real diode lets perhaps

10 microamps through -- not a lot, but still not perfect. And if you apply enough reverse

voltage (V), the junction breaks down and lets current through. Usually, the breakdown

voltage is a lot more voltage than the circuit will ever see, so it is irrelevant. (acts as a

high resistor)

When forward-biased, there is a small amount of voltage necessary to get the diode

going. In silicon, this voltage is about 0.6 - 0.7 volts. This voltage is needed to start the

hole-electron combination process at the junction. This type of semiconductor acts as a

small resistor. It does not obey Ohm’s Law!

One major use of a diode is to convert AC voltage to a voltage that has only one polarity.

When a diode is used in a circuit for this purpose it is called a rectifier.

LEDs – Light Emitting Diodes: Diodes can do more than provide one-way paths for

current. Diodes made from combinations of gallium and aluminum with arsenic and

phosphorus emit light when they are forward-biased. When electrons reach the holes in

the junction, they recombine and release the excess energy at the wavelengths of light.

This happens in any diode, but you can only see the photons when the diode is composed

of certain material. These diodes are called light-emitting diodes (LEDs). Basically,

LEDs are just tiny light bulbs that fit easily into an electrical circuit. But unlike ordinary

incandescent bulbs, they don't have a filament that will burn out, and they don't get

especially hot. They are illuminated solely by the movement of electrons in a

semiconductor material, and they last just as long as a standard transistor.

Benefits of LEDs and IREDs, compared with incandescent and fluorescent illuminating

devices, include:

Low power requirement: Most types can be operated with battery power

supplies.

High efficiency: Most of the power supplied to an LED or IRED is converted into

radiation in the desired form, with minimal heat production.

Long life: When properly installed, an LED or IRED can function for decades.

Typical applications include:

Indicator lights: These can be two-state (i.e., on/off), bar-graph, or alphabetic-

numeric readouts.

LCD panel backlighting: Specialized white LEDs are used in flat-panel

computer displays.

Fiber optic data transmission: Ease of modulation allows wide communications

bandwidth with minimal noise, resulting in high speed and accuracy.

Remote control: Most home-entertainment "remotes" use IREDs to transmit data

to the main unit.

Both CD players and supermarket scanners must detect the laser light reflected

from the CD or bar code. Diodes can detect light as well as emit it. A reverse-

biased pn-junction diode is usually is usually used as a light detector. Light

falling on the junction creates pairs of electrons and holes. These are pulled

toward the ends of the diode, resulting in a current that depends on the light

intensity.

Transistors: A transistor is a simple device made of doped semiconducting material that

is used in most electronic circuits. It usually consists of three terminals with one type of

semiconductor sandwiched between two layers of the other type (npn or pnp). The

central layer is called the base. The two surrounding regions are the emitter and the

collector. The pn-junctions in the transistor can be thought of as two back-to-back diodes.

Transistors act as miniature electronic switches. They are the building blocks of the

microprocessor which is the brain of the computer. Similar to a basic light switch,

transistors have two operating positions, on and off. This on/off, or binary, functionality

of transistors enables the processing of information in a computer.

The emitter/base junction is forward biased. The collector/base junction is reversed biased.

PROCEDURES/ACTIVITIES

Day 1: 1) Inquire about the students’ prior knowledge of semiconductors,

energy levels and bands, and dopants. They should have had

some previous education on these subjects in chemistry.

2) Inquire about the students’ knowledge about the important

uses of semiconductors in our modern world.

3) Show power point to help students visualize the lesson. (This

may have to continue into day 2). I find it useful to print out

the power points as notes for my students. This way I have

their attention instead of them rushing to write down every

word they see. I also include my power points on my website

so the students may go back and review. You may need to add

or remove slides due to the depth and breadth of the subject

matter you would like to cover. I will, also, stop periodically

and further explain items on the board or overhead. For

example, with energy bands I may want to draw the Energy vs.

Atomic Separation graphs for two, four and many atoms (pg.

869 – Holt Physics). This breaks up the monotony of me

reading off slides and has the students more involved.

4) Answer any questions the students may have.

Day 2:

1) Begin class by asking for questions or comments about the

previous day’s lesson. Complete power point if needed.

2) To emphasize the movement of holes and electrons have the

students participate in the following demonstrations.

Demonstration 1:

Hole Flow

Purpose: To illustrate hole flow.

Materials: nine rubber stopper

Procedure: Choose 10 students to stand facing the class with their right

palms out. Place a stopper in the hand of every person except the student

on the far right. Beginning at the far right, have each student look to their

right and place their stopper in their neighbor’s palm if that person does

not already have a stopper. All the stoppers will shift one palm to the right,

and the person on the far left will be without a stopper. Ask the students

to consider the movement of the empty space as an electron “hole”. Point

out that the hole moves to the left as the stoppers (the electrons) move to

the right.

Demonstration 2:

n-type Semiconductors

Purpose: To illustrate an n-type semiconductor.

Materials: 11 rubber stoppers

Procedure: Have the same 10 students (or choose different students)

stand facing the class with both palms held out. Place a stopper in the

right hand of everyone except for the student on the far left, who should

have two stoppers. Beginning with the student on the left, have each

student look to their right and place one stopper in their neighbor’s palm,

if they themselves have more stoppers than their neighbor. The extra

stopper will shift to the right, and, at the end, the person on the far right

will have an extra stopper. Have the students consider the movement of

the extra stopper as that of an electron. The type of material demonstrated

appears to be electron-rich, as in n-type semiconductors. Explain that the

process of adding impurities to semiconductors is called doping.

Demonstration 3:

p-type Semiconductors

Purpose: To illustrate a p-type semiconductor.

Materials: 19 rubber stoppers

Procedure: Have the same 10 students (or choose different students)

stand facing the class with both palms held out. Place a stopper in the left

and right hands of everyone except for the student on the far right, who

should only have one stopper. Beginning at the far right, have each

student place one stopper in their neighbor's (to the right) palm, if they

have an empty hand. Eventually, the person on the far left will have one

less stopper. Point out that the ”hole” has moved to the left as the stoppers

moved to the right. The type of material demonstrated appears to be hole

rich.

3) Pass around various parts of a circuit (transistors, LEDs,

microprocessors, etched silicon chips – many times you can ask

manufactures to send you rejected chips for demonstration

purposes).

4) Have the students write a short essay (1-2 pgs. can be a journal

activity) about transistors (see essay sheet and rubric)

http://www.sciencenetlinks.com/lessons.cfm?DocID=140

5) Pass out the lab procedures for Day 3, so the students have time to

get acquainted with the procedures.

DAY 3: 1) If you have not completed the activities from Day 2 continue

before lab.

2) Lab Day – THE STOPLIGHT LAB (LEDs diodes); review

lab procedures and either perform as a group activity or a

class project (dependent on the amount of materials).

DAY 4 and Beyond: Extension Activity

1) There has been great concern over the disposal of electronics due

to lead and other heavy elements within these appliances. I have

found a great website that has a lesson plan pertaining to this.

http://www.ateec.org/curric/themes/envrisk/computers.html

2) Another activity is to have students research alternatives to using

lead in electronics and legislation requiring the use of these

alternatives.

http://www.tsrtp.ucdavis.edu/newsletters/summer_2002/LeadSold

ers.html

http://www.tms.org/pubs/journals/JOM/9903/Frear-9903.html

http://www.imaps.org/adv_micro/2002may_jun/4.html

THE STOPLIGHT

PROBLEM: How can you design a circuit so that changing the direction of the current

changes the LED that light up?

SAFETY:

MATERIALS:

0- to 12-V variable power supply

Red LED

Green LED

Bi-colored LED

Wires

470- resistor

Voltmeter

PROCEDURE:

1. Connect a series circuit with the power supply, the resistor, and the red and

green LEDs to them both. Do not bypass or omit the resistor with an LED.

Always have the resistor between an LED and one side of the power

supply.

2. Reverse the direction of the current in the circuit and note the result.

Measure the voltage across an LED.

3. Connect a parallel circuit with the power supply, the resistor, and the red

and green LEDs to light them both. Do not bypass or omit the resistor

with an LED. Always have the resistor between an LED and one side

of the power supply.

4. Reverse the direction of the current in the circuit and note the result.

Measure the voltage across an LED.

1 (Glencoe Physics: Principals and Problems 2002)

5. Repeat steps 1-4 with the bi-colored LED instead of the separate red and

green LEDs. Remember to leave the resistor connected to the power

supply.

DATA AND OBSERVATIONS:

1. What voltage was needed to light the LEDs in each circuit?

2. Describe what happened when the current was reversed in each of the

circuits?

3. Make a drawing of the stoplight circuit that will allow: the red on, green

off; green on, red off.

4. Is this a series or parallel circuit? Why does it work this way?

5. What change would you observe if you replaced the resistor with a 330-

resistor?

6. If the voltage across the LED was increased, what would happen to the

current?

2 (Glencoe Physics: Principals and Problems 2002)

7. What must be true for the graph of current vs. voltage to be a straight line?

8. How does an LED differ from a 60-W light bulb?

9. Sketch a graph of the following data describing the relationship between

the current and the voltage.

VOLTAGE (V) CURRENT (A)

0.5 0.001

1.0 0.002

1.5 0.030

What does the graph indicate about the resistance of the LED? Is this an

Ohmic or non-Ohmic material?

3 (Glencoe Physics: Principals and Problems 2002)

TEACHER INFORMATION AND RUBRIC FOR STOPLIGHT LAB

*Students likely have little familiarity with the basic structures of solid state devices.

Students will sometimes confuse filament lamps with LEDs.

*DO NOT omit the current limiting resistor – excessive current can destroy LEDs.

Depending on the number of students in your class and the amount of equipment

you have you can put the students into groups of two to four. If you do not have

enough equipment for groups you may perform this as a class activity.

Purchasing Equipment: Here are a few websites that you should be able to order

with, if you do not already have the supplies.

Exploratorium Museum Store - http://www.exploratoriumstore.com/ Science toys and games, puzzles, gifts, books, classroom resources, charts and posters, videos, and software.

PASCO Scientific - http://www.pasco.com/ Offers a variety of interfaces and sensors (probes) bundled with computer-based activities for chemistry, biology, physics and general science.

Flinn Scientific - http://www.flinnsci.com/ Sells educational science supplies. Site has especially useful information on lab safety and lab design.

Sargent-Welch - http://www.sargentwelch.com/ Distributor of thousands of grades K-14 scientific, educational items ranging from basic glassware to hands-on curriculum products.

Vernier Software - http://www.vernier.com/ Maker of science hardware and software for the classroom, especially CBL products, probes, and TI programmable calculator programs.

Educational Innovations - http://www.teachersource.com/ Source for inexpensive and hard-to-find science workshop supplies and materials for the lab, classroom, school workshop, university and home experimenter.

Fisher Science Education - http://www.fisheredu.com/ Thousands of science products geared toward the K-12 education market.

Cambridge Physics Outlet - http://www.cpo.com/ Equipment and software for inquiry-based hands-on teaching of integrated math, science, and technology. Also, there are interactive science puzzlers and an online products catalog

The Science Source - http://www.thesciencesource.com/ Offers science kits, toys, supplies, materials, classroom kits, and other science products. Much of the product line evolved out of curricula developed by the Physical Science Study Committee (PSSC) at MIT and Project Physics at Harvard University, and products are available through distributors or online

Frey Scientific - http://www.freyscientific.com/ Scientific supplies and other materials for middle and high schools.

Rubrics and Evaluations: The following pages include the answer sheet to the lab

and two different rubrics. The first rubric is for a non-formal lab report (class

activity) and the second is for a typed, formal report. It is the teacher’s discretion to

choose which one to use.

TEACHER ANSWER SHEET FOR STOPLIGHT

LAB QUESTIONS

1) What voltage was needed to light the LEDs in each circuit?

The LEDs will begin to glow around 1.8 V and be bright at 2.2 V.

2) Describe what happened when the current was reversed in each of

the circuits?

Reversing the current causes both LEDs to go out.

3) Make a drawing of the stoplight circuit that will allow: the red on,

green off; green on, red off.

The stoplight circuit will have the LEDs in parallel and reversed in

polarity.

4) Is this a series or parallel circuit? Why does it work this way?

It is a series circuit. However, to light both the red and green

LEDs at the same time, the LEDs must be connected in parallel.

By reversing the polarity of the LEDs, only one color can be on at

a time. Reversing the leads at the power supply will change the

color of the stoplight.

5) What change would you observe if you replaced the resistor with a

330- resistor?

The 330- resistor allows more current to flow through the circuit,

causing the LEDs to glow more brightly.

6) If the voltage across the LED was increased, what would happen to

the current?

Because V = IR (for Ohmic materials), student will likely indicate

that current increases as voltage increases.

7) What must be true for the graph of current vs. voltage to be a

straight line?

The graph will be a straight line only if the resistance remains

constant (if it is Ohmic). It is not. These LEDs are non-Ohmic

materials, meaning they do not follow Ohm’s Law.

8) How does an LED differ from a 60-W light bulb?

A lightbulb emits a broad range of the electromagnetic spectrum,

whereas a LED emits a single wavelength only. In addition,

current can pass either way across a lightbulb filament but only in

one direction through an LED.

9) Sketch a graph of the following data describing the relationship

between the current and the voltage.

VOLTAGE (V) CURRENT (A)

0.5 0.001

1.0 0.002

1.5 0.030

What does the graph indicate about the resistance of the LED? Is this an

Ohmic or non-Ohmic material?

The relationship is not linear. Therefore, resistance of the LED is not

constant and the material is non-Ohmic.

At 1.0 V the resistance is 500 and at 1.5 V the resistance is 50 .

Voltage (V) Current (A) Resistance ( )

0.5 0.001 500 1 0.002 500

1.5 0.03 50

Current vs. Voltage in a LED

-0.005

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0 0.5 1 1.5 2

Voltage (Volts)

Cu

rren

t (A

mp

ere

s)

Series1

THE STOPLIGHT RUBRIC

Name: _______________________________ Date: _____________ Period: _______

EXCELLENT GOOD FAIR POOR

QUESTIONS

(60 POINTS)

Student answered all

questions clearly and

accurately.

60/52 points

Student answered

most (6-7) questions

clearly and

accurately.

51/43 points

Student answered

some (4-5)

questions clearly

and accurately.

42/36 points

Student answered

few (less than 4)

questions clearly

and accurately.

35/0 points

DIAGRAMS

(15 POINTS)

Student’s diagrams

were very neat and

accurate and followed

all schematic

guidelines.

15/14 points

Student’s diagrams

were accurate and

followed all to most

schematic guidelines.

13/12 points

Student’s diagrams

were fairly accurate

and followed some

schematic

guidelines.

11/10 points

Student’s

diagrams were

messy and

inaccurate and

followed few

schematic

guidelines.

9/0 points

GRAPH

(15 POINTS)

Student’s graph was

very neat and

accurate. All

components were

included (title, axes

names and units, line

connecting data

points)

15/14 points

Student’s graph was

accurate. All to most

components were

included (title, axes

names and units, line

connecting data

points)

13/12 points

Student’s graph

was fairly accurate.

Some components

were included (title,

axes names and

units, line

connecting data

points)

11/10 points

Student’s graph

was messy and

inaccurate. Few

components were

included (title,

axes names and

units, line

connecting data

points)

9/0 points

SPELLING,

GRAMMAR AND

ORGANIZATION

(5 POINTS)

Student’s written

work was

exceptionally neat

and organized and

had no grammatical

or spelling errors.

5 points

Student’s written

work was neat and

organized and had no

or very few

grammatical or

spelling errors.

4 points

Student’s written

work was organized

but had some

grammatical or

spelling errors.

3/2 points

Student’s written

work was poorly

organized and had

many grammatical

or spelling errors.

1 point

PARTICIPATION

(5 POINTS)

Student was a very

active participant in

all aspects of the lab

and worked very well

in a group setting.

5 points

Student actively

participated in most

aspects of the lab and

worked well in group

setting.

4 points

Student actively

participated in

some aspects of the

lab and worked

well most of the

time in group

setting.

3/2 points

Student was rarely

(if at all) engaged

or participated

with group

members.

1/0 point

THE STOPLIGHT RUBRIC: LAB REPORT

Name: _______________________________ Date: _____________ Period: _______

Excellent 5 POINTS

Good 4 POINTS

Satisfactory 3 POINTS

Needs Improvement 2 POINTS

Components of the Report

All required elements are present and additional elements that add to the report (e.g., thoughtful

comments, graphics) have been added.

All required elements are present.

One required element is missing, but additional elements that add to the report (e.g., thoughtful

comments, graphics) have been added.

Several required elements are missing.

Question / Purpose

The purpose of the lab or the question to be answered during the lab is clearly identified and stated.

The purpose of the lab or the question to be answered during the lab is identified, but is stated in a somewhat unclear manner.

The purpose of the lab or the question to be answered during the lab is partially identified, and is stated in a somewhat unclear manner.

The purpose of the lab or the question to be answered during the lab is erroneous or irrelevant.

Spelling, Punctuation, Grammar

One or fewer errors in spelling, punctuation and grammar in the report.

Two or three errors in spelling, punctuation and grammar in the report.

Four errors in spelling, punctuation and grammar in the report.

More than four errors in spelling, punctuation and grammar in the report.

Drawings / Diagrams

Clear, accurate diagrams are included and make the experiment easier to understand. Diagrams are labeled neatly and

accurately.

Diagrams are included and are labeled neatly and accurately.

Diagrams are included and are labeled.

Needed diagrams are missing OR are missing important labels.

Participation Used time well in lab and focused attention on the experiment.

Used time pretty well. Stayed focused on the experiment most of the time.

Did the lab but did not appear very interested. Focus was lost on several occasions.

Participation was minimal OR student was hostile about participating.

Error Analysis Experimental errors, their possible effects, and ways to reduce errors are discussed.

Experimental errors and their possible effects are discussed.

Experimental errors are mentioned.

There is no discussion of errors.

Procedures Procedures are listed in clear steps. Each step is numbered and is a complete sentence.

Procedures are listed in a logical order, but steps are not numbered and/or are not in complete sentences.

Procedures are listed but are not in a logical order or are difficult to follow.

Procedures do not accurately list the steps of the experiment.

Summary Summary describes the skills learned, the information learned and

some future applications to real life situations.

Summary describes the information learned and a possible application to

a real life situation.

Summary describes the information learned.

No summary is written.

Calculations All calculations are shown and the results are correct and labeled appropriately.

Some calculations are shown and the results are correct and labeled appropriately.

Some calculations are shown and the results labeled appropriately.

No calculations are shown OR results are inaccurate or mislabeled.

Materials / Setup All materials and setup used in the experiment are

clearly and accurately described.

Almost all materials and the setup used in the

experiment are clearly and accurately described.

Most of the materials and the setup used in the

experiment are accurately described.

Many materials are described inaccurately OR

are not described at all.

Conclusion Conclusion includes whether the findings supported the hypothesis,

Conclusion includes whether the findings supported the hypothesis

Conclusion includes what was learned from the experiment.

No conclusion was included in the report OR shows little effort and reflection.

possible sources of error, and what was learned from the experiment.

and what was learned from the experiment.

Variables The relationship between

the variables is discussed and trends/patterns logically analyzed. Predictions are made about what might happen if part of the lab were changed or how the experimental design could be changed.

The relationship between

the variables is discussed and trends/patterns logically analyzed.

The relationship between

the variables is discussed but no patterns, trends or predictions are made based on the data.

The relationship between the

variables is not discussed.

Safety Lab is carried out with full attention to relevant safety procedures. The set-up, experiment, and tear-down posed no safety threat to any individual.

Lab is generally carried out with attention to relevant safety procedures. The set-up, experiment, and tear-down posed no safety threat to any individual, but one safety procedure

needs to be reviewed.

Lab is carried out with some attention to relevant safety procedures. The set-up, experiment, and tear-down posed no safety threat to any individual, but several safety procedures need to be

reviewed.

Safety procedures were ignored and/or some aspect of the experiment posed a threat to the safety of the student or others.

Replicability Procedures appear to be replicable. Steps are outlined sequentially and are adequately detailed.

Procedures appear to be replicable. Steps are outlined and are adequately detailed.

All steps are outlined, but there is not enough detail to replicate procedures.

Several steps are not outlined AND there is not enough detail to replicate procedures.

Scientific Concepts

Report illustrates an accurate and thorough understanding of scientific

concepts underlying the lab.

Report illustrates an accurate understanding of most scientific

concepts underlying the lab.

Report illustrates a limited understanding of scientific concepts underlying the

lab.

Report illustrates inaccurate understanding of scientific concepts underlying the lab.

Questions Report has thoroughly and accurately answered all questions posed in lab

Report has accurately answered all questions posed in lab.

Report has accurately answered most questions posed in lab.

Report has accurately answered a few questions posed in lab.

Experimental Design

Experimental design is a well-constructed test of the stated hypothesis.

Experimental design is adequate to test the hypothesis, but leaves some unanswered

questions.

Experimental design is relevant to the hypothesis, but is not a complete test.

Experimental design is not relevant to the hypothesis.

Data Professional looking and accurate representation of the data in tables and/or graphs. Graphs and tables are labeled and titled.

Accurate representation of the data in tables and/or graphs. Graphs and tables are labeled and titled.

Accurate representation of the data in written form, but no graphs or tables are presented.

Data are not shown OR are inaccurate.

Appearance / Organization

Lab report is typed and uses headings and

subheadings to visually organize the material.

Lab report is neatly handwritten and uses

headings and subheadings to visually organize the material.

Lab report is neatly written or typed, but formatting

does not help visually organize the material.

Lab report is handwritten and looks sloppy with cross-

outs, multiple erasures and/or tears and creases.

Experimental Hypothesis

Hypothesized relationship between the variables and the predicted results is clear and reasonable based on what has been

studied.

Hypothesized relationship between the variables and the predicted results is reasonable based on

general knowledge and observations.

Hypothesized relationship between the variables and the predicted results has been stated, but appears to be based on flawed

logic.

No hypothesis has been stated.

TRANSISTOR WRITING ASSIGNMENT

This assignment is due: ________________.

Directions: Write a 2-3 page, typed essay (12 pt type, must start at

top of page, doubled spaced) on the topic of transistors. Be sure to

answer the following questions within your essay and include any

references (Reference page does not count towards paper!)

• When was the transistor developed and by whom?

What was the problem that the developers of the

transistor were trying to solve?

• Describe some early uses of the transistor (At least

three).

• What were the advantages of the transistor over the

vacuum tube?

• How are transistors used today?

• In what way has the transistor changed modern life?

Give specific examples.

TRANSISTOR WRITING ASSIGNMENT

RUBRIC

Name: _______________________________ Date: _____________ Period: _______

Poor Fair Good Excellent Content &

Development 50 pts

- Content is

incomplete. - Major points are not clear

and /or persuasive. (Only 2 out of the 5

questions have been addressed)

(0 to 33 points)

- Content is not

comprehensive and /or persuasive. - Major points

are addressed, but not well supported. - Content

is inconsistent with regard to purpose and clarity of

thought. (Only 3 out of the 5 questions have

been addressed)

(34 to 40 points)

- Content is

comprehensive, accurate, and persuasive. - Major

points are stated clearly and are well supported. -

Content and purpose of the writing are clear.(4 to

5 of the questions were addressed)

(41 to 44 points)

- Content is

comprehensive, accurate, and persuasive. - Major

points are stated very clearly and are well

supported. - Content and purpose of the writing are

clear and has gone beyond expectations. (All

questions were exceptionally addressed)

(45 to 50 points)

Organization

& Structure 20 pts

- Organization and

structure detract from the message of

the writer. - Paragraphs are

disjointed and lack transition of

thoughts. (0 to 13 points)

- Structure of the paper is

not easy to follow. - Paragraph transitions

need improvement.

(14 to 15 points)

- Structure of the paper is

clear and easy to follow. - Paragraph transitions are

present and logical and maintain the flow of

thought throughout the paper.

(16 to 17 points)

- Structure of the paper is

very clear and easy to follow. - Paragraph

transitions are present and very logical and maintain

the flow of thought throughout the paper.

(18 to 20 points)

Format and References

20 pts

- Paper lacks many elements of correct

formatting. –ex) Paper is not typed

and over/under page length, incorrect font

point, and no references are

included. (0 to 13 points)

- Paper follows most guidelines. –ex) Paper is

not typed or over/ under page length, or incorrect

font point, or no references are included.

(14 to 15 points)

- Paper follows designated guidelines and

includes references.

(16 to 17 points)

- Paper follows exact designated guidelines and

includes references in correct manner.

(18 to 20 points)

Grammar, Punctuation

& Spelling

10 pts

- Paper contains numerous

grammatical,

punctuation, and spelling errors. -

Language uses jargon or

conversational tone. (0 to 5 points)

- Paper contains few grammatical, punctuation

and spelling errors. -

Language lacks clarity or includes the use of some

jargon or conversational tone.

(6 points)

- Rules of grammar, usage, and punctuation

are followed; spelling is

correct. - Language is clear and precise;

sentences display consistently strong,

varied structure. (7 to 8 points)

- Rules of grammar, usage, and punctuation

are followed completely;

spelling is correct. - Language is very clear and

precise; sentences display consistently strong, varied

structure. (9 to 10 points)

MATERIALS

• Computer with PowerPoint capabilities

• LCD Projector

• Screen

• 19 Rubber stoppers (or similar object)

• 0 to 12-V variable power supplies

• Red LEDs

• Green LEDs

• Bi-colored LEDs

• Wires

• 470- resistors

• Voltmeters

• Various transistors, diodes, microprocessors, etc

REFERENCES

Serway, Raymond A., and Jerry S. Faughn. Holt Physics. Austin, Texas:

Holt, Rinehart and Winston, 2000.

Zitzewitz, Paul W., Ph.D, et al. Glencoe Physics: Principles and Problems.

Columbus, Ohio: Glencoe/McGraw-Hill, 2002.

The MAD Scientist Network. 1995-2001 or 30 Feb. 1906. Washington U

School of Medicine. 10 Oct. 2005. <http://www.madsci.org>.

Chem4Kids.com 1997-2007. Andrew Rader Studios.

< http://www.chem4kids.com/files/elements/014_shells.html>

Intel.com <http://www.intel.com/education/transworks/flat6.htm>

Energy Efficiencey and Renewable Energy (EERE). U.S. Department of Energy.

01/03/2006. <http://www1.eere.energy.gov/solar/doping_silicon.html>

BobEmery Catholic Schools Diocese of Maitland, Newcastle 2002.

03/21/07.<http://webs.mn.catholic.edu.au/physics/emery/hsc_ideas_implemen

tation.htm#semi

SatCure (Car, Hobby Electronics and Books).

<http://www.satcure-focus.com/tutor/page4.htm>

Fun with Transistors.08/27/2006 Max Robinson.09/06/2006.

< http://www.angelfire.com/planet/funwithtransistors/Basics_03_Sc_Diodes.html>

Rubrics. Utah Education Network.

< http://www.uen.org/Rubric/rubric.cgi?rubric_id=25>

MadLab.1995-2006. MadLab Ltd.

<http://www.madlab.org/electrnx/lesson4.html>

Multidisciplinary Activities: Environmental Risk– What Do You Do With Your

Old

Computers? 2001. ©ATEEL. 02/27/02.

<http://www.ateec.org/curric/themes/envrisk/computers.html>

http://www3.sympatico.ca/silver.fox/Diodes1.html

http://www.ece.gatech.edu/research/labs/vc/theory/doping.html