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
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Systems, order, and organization.
Evidence, models, and explanation.
Change, constancy, and measurement.
Evolution and equilibrium.
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Form and function.
CONTENT STANDARD B: SCIENCE AS INQUIRY
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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
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Structures of atoms.
Structure and properties of matter.
Interactions of energy and matter.
CONTENT STANDARD E: SCIENCE AND TECHNOLOGY
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Abilities of technological design
Understandings about science and technology
CONTENT STANDARD F: SCIENCE IN PERSONAL AND SOCIAL
PERSPECTIVES
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Science and technology in local, national, and global challenges
CONTENT STANDARD G: HISTORY AND NATURE OF SCIENCE
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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 pdopant, 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.
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•
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 alphabeticnumeric 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 reversebiased 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.
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).
2)
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)
0.5
1.0
1.5
CURRENT (A)
0.001
0.002
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)
0.5
1.0
1.5
CURRENT (A)
0.001
0.002
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)
0.5
1
1.5
Current (A)
0.001
0.002
0.03
Resistance ()
500
500
50
Current vs. Voltage in a LED
Current (Amperes)
0.035
0.03
0.025
0.02
0.015
Series1
0.01
0.005
0
-0.005 0
0.5
1
1.5
Voltage (Volts)
2
THE STOPLIGHT RUBRIC
Name: _______________________________ Date: _____________ Period: _______
QUESTIONS
(60 POINTS)
DIAGRAMS
(15 POINTS)
EXCELLENT
Student answered all
questions clearly and
accurately.
GOOD
Student answered
most (6-7) questions
clearly and
accurately.
60/52 points
51/43 points
Student’s diagrams
Student’s diagrams
were very neat and
were accurate and
accurate and followed followed all to most
all schematic
schematic guidelines.
guidelines.
15/14 points
Student’s graph was
very neat and
accurate. All
components were
included (title, axes
names and units, line
connecting data
points)
13/12 points
Student’s graph was
accurate. All to most
components were
included (title, axes
names and units, line
connecting data
points)
15/14 points
SPELLING,
Student’s written
GRAMMAR AND work was
ORGANIZATION exceptionally neat
(5 POINTS)
and organized and
had no grammatical
or spelling errors.
5 points
PARTICIPATION Student was a very
(5 POINTS)
active participant in
all aspects of the lab
and worked very well
in a group setting.
13/12 points
Student’s written
work was neat and
organized and had no
or very few
grammatical or
spelling errors.
4 points
Student actively
participated in most
aspects of the lab and
worked well in group
setting.
GRAPH
(15 POINTS)
5 points
4 points
FAIR
Student answered
some (4-5)
questions clearly
and accurately.
42/36 points
Student’s diagrams
were fairly accurate
and followed some
schematic
guidelines.
POOR
Student answered
few (less than 4)
questions clearly
and accurately.
35/0 points
Student’s
diagrams were
messy and
inaccurate and
followed few
schematic
guidelines.
11/10 points
9/0 points
Student’s graph
Student’s graph
was fairly accurate. was messy and
Some components
inaccurate. Few
were included (title, components were
axes names and
included (title,
units, line
axes names and
connecting data
units, line
points)
connecting data
points)
11/10 points
9/0 points
Student’s written
Student’s written
work was organized work was poorly
but had some
organized and had
grammatical or
many grammatical
spelling errors.
or spelling errors.
3/2 points
Student actively
participated in
some aspects of the
lab and worked
well most of the
time in group
setting.
1 point
Student was rarely
(if at all) engaged
or participated
with group
members.
3/2 points
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 One required element is
Several required elements
present.
missing, but additional
are missing.
elements that add to the
report (e.g., thoughtful
comments, graphics) have
been added.
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.
Spelling,
Punctuation,
Grammar
One or fewer errors in
spelling, punctuation and
grammar in the report.
Two or three errors in
Four errors in spelling,
spelling, punctuation and punctuation and grammar
grammar in the report.
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
Procedures do not
are not in a logical order or accurately list the steps of
are difficult to follow.
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
Conclusion includes what
whether the findings
was learned from the
supported the hypothesis experiment.
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.
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 teardown 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
Experimental design is not
relevant to the hypothesis, relevant to the hypothesis.
but is not a complete test.
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 Data are not shown OR are
the data in written form,
inaccurate.
but no graphs or tables
are presented.
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.
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 No hypothesis has been
between the variables and stated.
the predicted results has
been stated, but appears
to be based on flawed
logic.
Lab report is handwritten
and looks sloppy with crossouts, multiple erasures
and/or tears and creases.
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: _______
Content &
Development
50 pts
Organization
& Structure
20 pts
Format and
References
20 pts
Grammar,
Punctuation
& Spelling
10 pts
Poor
Fair
Good
Excellent
- Content is
incomplete. - Major
points are not clear
and /or persuasive.
(Only 2 out of the 5
questions have been
addressed)
- 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)
- 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)
- 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)
(0 to 33 points)
- Organization and
structure detract
from the message of
the writer. Paragraphs are
disjointed and lack
transition of
thoughts.
(0 to 13 points)
- 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 contains
numerous
grammatical,
punctuation, and
spelling errors. Language uses
jargon or
conversational tone.
(0 to 5 points)
(34 to 40 points)
- Structure of the paper is
not easy to follow. Paragraph transitions
need improvement.
(41 to 44 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.
(45 to 50 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.
(14 to 15 points)
- Paper follows most
guidelines. –ex) Paper is
not typed or over/ under
page length, or incorrect
font point, or no
references are included.
(16 to 17 points)
- Paper follows
designated guidelines and
includes references.
(18 to 20 points)
- Paper follows exact
designated guidelines and
includes references in
correct manner.
(14 to 15 points)
- Paper contains few
grammatical, punctuation
and spelling errors. Language lacks clarity or
includes the use of some
jargon or conversational
tone.
(16 to 17 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)
(18 to 20 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)
(6 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, Newcastle2002.
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