Making Motors - How are Electricity and Magnetism Related?

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How Are Electricity and Magnetism Related?
Laurie Harris
Thomas Jefferson Middle School
[email protected]
Barbara Kuebler
Lewis and Clarck Middle School
[email protected]
Final Project for
Summer Physics Institute
Electricity and Magnetism
Dr. Meera Chandrasekhar
University of Missouri-Columbia
June 28, 2000
Concept
The relationship between electricity and magnetism.
Concept Illustration
As students work to build a motor they will discover the effect of each of the following
variables: different gauge wire, number of coils of wire, different size of batteries,
different size magnets, different shape magnets, and the diameter of the coil of wire.
Quantitative and Qualitative Applications
Students will be able to measure and calculate the amount of power generated by
a. coils of wire.
b. different size batteries.
c. different size magnets.
d. different gauge wire.
Students will be able to calculate the power using the following formula:
Power = current2 x resistance
Power = resistance x current
Background Information
Electricity: accumulation or movement of charged particles.
Electric Current: flow of negatively charged free electrons through a material.
Magnetism: magnetic force, which is also produced by the motion of charged particles.
A conductor passing through a magnetic field will produce an electric current or if a
current is passed through a conductor, which is in a magnetic field, a mechanical force is
produced.
An electric motor creates movement by placing current carrying coils in a magnetic field.
A common motor is made up of three major components; stator, commutator, and
armature/rotor. Commutator is the means by which an electrical connection is established
with the armature coils. The armature/rotor is a rotating wire coil placed in a magnetic
field. The brushes feed one coil with current and then its resulting magnetic field interacts
with that of the commutator causing the armature/rotor to turn slightly, as each coil is fed
in quick succession the armature/rotor spins. Electrical energy is changed to mechanical
energy.
Current flows through the wire coil and creates an electromagnet one face of the coil
becomes a north pole, the other a south pole. The field electromagnets attract its opposite
pole on the coil and repel its like pole, causing the coil to spin.
How Are Electricity and Magnetism Related
Laurie Harris
Barbara Kuebler
2
Electromagnetic Motor
This is a classic design from the 1938 book Things a Boy Can Do with Electricity by
Alfred Morgan. You can make this simple model electric motor with the following
materials:
• Block of wood, 6 x 4x _ inches (app. 152 x 101x 19 mm) — Cost $.16 each, 4 x 8
piece of plywood that is _ in thick, $20.90
• Three 20-penny nails — Cost $.05
• One 18-penny nail — Cost .03
• Two small nails — Cost $.02
• Two small screws — Cost $.04
• Glass tubing (short piece) or small test tube — Cost $.27
• Magnet wire, No. 20 to No. 24 — Cost $5.15 per spool
• Cork — Cost $.50
• Variety of batteries - Cost AA - $.60, D $.75, 6 volt $6.10, 9 volts $5.35.
• Optional: One knife switch, 2 bulb holders, 2 bulbs — Cost knife switch $2.25,
screw base receptacle $1.00, bulbs $.70 each
Using a hacksaw, cut the heads the heads off two twenty penny nails two _ inches
(70mm) from the point. Drill two small holes in the base on centers four 3/8 inches
(111mm) apart. Drive the cut nails into these holes until they stand 2 _ inches (57mm)
high above the base. These nails form the cores of the field magnets. The field magnets
supply the magnetic field in which the armature revolves.
How Are Electricity and Magnetism Related
Laurie Harris
Barbara Kuebler
3
The motor armature is 20-penny nail pushed into a hole in a large cork. The cork is
provided with a bearing made of glass tubing, which has been closed at one end by
holding in a flame. The piece of tubing should be about 1 _ (44 mm) long and _ inch (6
mm) in diameter.
A nail driven through from the underside of the base exactly halfway between the two
field cores in the pivot upon which the armature turns. Adjust the glass tubing in the cork
until the ends of the armature (nail) are level with the upper ends of the field core (nails).
Each field core is wound with four layers of No. 20 to No. 24 magnet wire. Both coils
are wound in the same direction. The armature is also wound with four layers of wire
(of the same size as that used for the field). The armature winding is divided into two
sections, one on each side of the cork. Both sections are wound in the same direction.
The nail should be wrapped with two or three layers of thin paper before the wire is
wound in place.
The terminals of the armature winding are scraped bare of insulation and fastened to the
glass tube so as to form what is known as the commutator. It is by means of the
commutator that electrical connection is established with the revolving armature coils.
The wires are fastened to the tubing with thread or narrow strips of adhesive tape.
The outside terminals of the field windings should each be connected to a binding post.
The inside terminals are scraped bare of insulation and used as brushes. The brushes are
fastened in position by wrapping each one around a small nail or brad driven into the
wooden base.
Connect several dry cells to the binding posts. Make certain everything is wound and
connected correctly, and that the brushes are in the right position. Give the armature a
twirl with your fingers, and the motor should turn.
How Are Electricity and Magnetism Related
Laurie Harris
Barbara Kuebler
4
The Johnson DC Electric Motor
Material Required
• Approximately 2 meters of 26 gauge magnet wire (also known as motor rewind wire)
— Cost $5.15 per spool
• Approximately 60 cm of 10 gauge or larger ground wire (4 gauge shown) — Cost
$4.40 for 6 meters
• Magnets — Cost $2.58
• Batteries of varying voltages Cost AA - $.60, D $.75, 6 volt $6.10, 9 volts $5.35.
• Electrical tape — Cost $1.50 per roll
• Small piece of plywood (6 x 6 or so) — Cost $.16 each, a 4 x 8 piece of plywood _
inch thick $20.90
Make a coil with the magnet wire by wrapping it around something with a diameter
smaller than the length of the battery. Use a small piece of tape at the ends to hold it
together.
How Are Electricity and Magnetism Related
Laurie Harris
Barbara Kuebler
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Bend the ground wire as shown to form the arms of the motor. Drill holes in the wood
base for the arms. Arms are to be the length of the battery apart.
Questions to guide student thinking
1. Can electrical energy be changed to mechanical energy?
2. Will a six volt battery produce as much current as a nine volt battery?
3. Does the gauge of the wire make a difference in the current flow?
4. What happens if you add coils to the armature?
5. How does the magnet affect the rotation of the motor?
6. If you use more than one magnet, does it change the rotation? Why?
7. What happens as the magnet size increases?
8. Trace the path of the current through the motor.
How Are Electricity and Magnetism Related
Laurie Harris
Barbara Kuebler
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9. How does electromagnetic force aid or oppose this motor?
Electromagnetic Theory
Name __________________________________________________Hour ________
Vocabulary:
Electromagnetic — a magnet that only attracts when electric current is connected to a
power source.
Current Flow —transfer of energy along a conductor by the movement of electrons.
Electrical Potential — a measure of the ability of a battery or other power source to do
work. Measured in volts.
Magnet — a material, which exhibits the unique property of attracting pieces of iron
and steel.
Armature — a rotating wire coil placed in a magnetic field. Armatures are found in
generators and motors.
Johnson s DC Motor Data Table
Battery Size
Turns per 10 seconds
Gauge Wire
Turns per 10 seconds
Number of Coils
Turns per 10 seconds
How Are Electricity and Magnetism Related
Laurie Harris
Barbara Kuebler
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Number of Magnets
Turns per 10 seconds
Position of Magnets
Turns per 10 seconds
Answer the following questions:
1. Can electrical energy be changed to mechanical energy?
2. Will a six volt battery produce as much current as a nine volt battery?
3. Does the gauge of the wire make a difference in the current flow?
4. What happens if you add coils to the armature?
5. How does the magnet affect the rotation of the motor?
6. If you use more than one magnet, does it change the rotation? Why?
7. What happens as the magnet size increases?
8. Trace the path of the current through the motor
9. How does electromagnetic force aid or oppose this motor?
Johnson s DC Motor Experimental Design Project
Use your Johnson s DC Motor to design an experiment and prepare a report to
demonstrate how one of the following affect the flow of electrons in the motor.
a. different coils of wire
b. different voltage of batteries
c. different size of magnets
How Are Electricity and Magnetism Related
Laurie Harris
Barbara Kuebler
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d. different gauge wire
The experiments and presentations will be graded on the following criterion:
Title: Make sure it relates to the Independent Variable and Dependent Variable. (5
points)
Introduction: Describe the rational, purposes, and hypothesis for the investigation.
(Remember an If then statement) (5 points)
Experimental Design: Make a box to include Independent Variable, Levels, Trials,
Dependent Variable, and Constants. (10 points)
Procedure: Make a DETAILED list of steps following to complete the investigation. (10
points)
Results: Complete a data table and graph for the data. (Remember title and unit of
measurement) (10 points)
Conclusion: Describe the purpose, major findings, and an explanation for the findings. (5
points)
In addition, points will be given for the presentation and visual representation of the
experiment. (10 points)
Please be prepared to present your experiment and be prepared to answer questions
concerning your data and observations.
History/Computers Relational study of Electromagnetic Theory
Have students work in groups to research some of the discoveries of the electromagnetic
theory.
Petrus Peregrinus
William Gilbert
Charles Coulomb
Hans Oersted
Andrea Ampere
Dominique Arago
Michael Faraday
James Maxwell
Georg Simon Ohm
Maria Goeppert-Mayer
Maria Agnesi
Lisa Meitner
How Are Electricity and Magnetism Related
Laurie Harris
Barbara Kuebler
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Irene Joliot-Curie
Rosiland Elsie Franklin
Magnets
Name________________________________________________________Hour______
Introduction: What makes magnets stick to your refrigerator? Why does rubbing a nail
with a magnet cause the nail to become a magnet, too?
Objective: Magnets are created when the magnetic domains of a substance are altered to
align all the individual domains in similar directions- with all positive charges in one
direction and all negative charges in the opposite direction. The opposing charges create
the opposites attract situation in which the NORTH side of a magnet is attracted to the
SOUTH side, while like sides repel each other. This alignment can be created by
exposure to electricity, contact with other magnets. Or by impact. In this activity, we will
investigate the attractive and repellant forces of magnets as well as the magnetic field
surrounding the magnets.
Procedure:
Testing Magnetic Poles
1. To determine which side of the magnet is North move the arrow end of your compass
around the magnet. The side of the magnet that the red arrow points toward is North. The
opposite side is South.
2. Mark your magnet sides N and S.
Magnetic Field Lines
3. In the next 3 steps, you will conduct the test on a separate sheet of paper and then
sketch your observations in the space provided on this sheet (smaller than your actual
results).
4. Single magnet:
a. Place a single magnet on its side on the counter.
b. Lay your blank sheet of paper across the top of the magnet.
N
S
(See Left)
c. Sprinkle (lightly) the surface the white paper with iron filings
2-3 inches away from the magnet in all directions.
d. Sketch the magnetic field lines below:
Paper on top
5. Two attracting magnets: a. Place two magnets, opposite sides facing, on the counter.
(See Below)
b. Repeat steps 4b — d and sketch your results below:
How Are Electricity and Magnetism Related
Laurie Harris
Barbara Kuebler
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N
S
N
S
Paper on Top
6. Two repelling magnets: a. Place two magnets, like sides facing, on the counter.
b. Repeat steps 4b — d and sketch your results below:
N
S
S
N
Paper on Top
Magnetic Strength
7. Test the strength of your magnet by hanging paper clips end-to-end from the bottom of
the magnet. Record the total number of paper clips in the chart below.
8. Repeat this test with both magnets stuck together to see if the number of magnets
affects magnetic strength.
Number of Magnets
1
2
3
4
Number of paper clips (strength)
Questions:
1. What happens in materials to cause them to become magnetized?
2. What three things commonly cause magnetism?
a.
b.
c.
3. What is the general shape of magnetic field lines?
4. Does the number of magnets have a significant effect on magnetic strength? What
is your evidence?
5. What happens to a nail that is rubbed by a magnet that causes it to become a
magnet?
How Are Electricity and Magnetism Related
Laurie Harris
Barbara Kuebler
11
Making An Electromagnet
Name______________________________________________________Hour________
Introduction: How do cranes use magnets to move scrap iron in junkyards? How do they
get those huge pieces of iron off of the magnet once they get it on the magnet?
Objective: Electricity can be used to temporarily align the magnetic domains within a
piece of iron in order to create an electromagnet. In this activity, we will use an iron nail,
copper wire, and a battery to construct an electromagnet that will then be tested to
determine how the number of wraps of wire around the nail, affect the strength of the
electromagnet.
Procedure:
1. Wrap the copper wire around the nail the designated number of times — allowing
at least about 4 inches at the end of the wire for connecting to the battery.
2. Connect the ends of the wire to opposite poles of the battery. This will complete
the circuit through the wire and create the electromagnetic field that will in turn
magnetize the iron nail.
3. To test the strength of the electromagnet, touch paper clips to the nail.
4. Stick as many paper clips to the nail as possible for each number of turns of
wire around the nail and record the maximum number in the chart on the next
page.
5. Remove all paper clips from the nail, add 5 more turns of wire, and test with
paper clips for the strength of the electromagnet.
6. Continue through all the designated numbers of wire turns.
7. Graph the number of wire turns versus the number of paper clips on the graph
provide.
How Are Electricity and Magnetism Related
Laurie Harris
Barbara Kuebler
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Data:
# Turns of Wire
# of
Paper Clips
5
10
15
20
25
30
35
40
45
50
55
Graph: Number of Turns Verses Strength
Questions:
1. According to your data, how does the number of turns of wire affect the strength
of the electromagnet?
2. What happens to the electromagnet when the wires are disconnected from the
battery?
3. What does the electricity do to the nail to cause it to become a temporary magnet?
4. What is an advantage of an electromagnet over an ordinary permanent magnet?
5. What kind of problem would you have if you used a permanent magnet strong
enough to pick up huge pieces of scrap iron?
How Are Electricity and Magnetism Related
Laurie Harris
Barbara Kuebler
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