VEA
Bringing Learning to Life
Program Support Notes
Middle - Senior High
25mins
DC Motors
Dr John Nicholson , B Sc
(Hons), Dip Ed, Ph D (La Trobe); Grad Dip
Comp Ed, M Ed (Melbourne)
Teacher Notes by
Produced by VEA Pty Ltd
Commissioning Editor Christine
Henderson B.Sc.
Ph.D. Dip.Ed.
McAuliffe Dip.Art (Film &
TV) Dip.Ed. B.Ed. Ph.D.
Executive Producer Mark
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DC Motors
For Teachers:
Introduction
This program looks at the origins and shapes of magnetic fields produced by both permanent
magnets and electromagnets. The work of Oersted and the origins of interactions between
magnetic fields and how this leads to the production of motion on demand are considered.
The origins of the first electric motor of Faraday and the rules for predicting field direction and
forces on current carriers is introduced and used in a number of demonstrations.
The construction of a simple DC electric motor is shown with useful graphics explaining the
purpose of the commutator and the various components of a DC motor. The various improvements
made to DC motors are then considered. The program concludes with some of the applications of
DC motors. The latest versions of brushless DC motors are also shown.
Throughout the program calculations are undertaken to demonstrate the various laws involving
magnetism and current including the Right Hand Slap rule.
Program Timeline
00:00:00
00:01:25
00:07:07
00:07:40
00:11:26
00:12:00
00:14:15
00:14:53
00:19:02
00:19:34
00:23:20
00:23:41
00:24:20
00:24:56
Introduction
Chapter 1– Electricity and Magnetism
Summary – Electricity and Magnetism
Chapter 2 – Useful Motion
Summary – Useful Motion
Chapter 3 – Making a DC Motor
Summary – Making a DC Motor
Chapter 4– Design Improvements
Summary – Design Improvements
Chapter 5– Application of DC Motors
Summary – Application of DC Motors
Conclusion
Credits
End Program
Website References
•
A useful website on Faraday and a variety of other early electrical devices!
http://www.sparkmuseum.com/MOTORS.HTM
•
A simple site that includes an applet of the a DC motor explaining /showing the commutator
http://www.walter-fendt.de/ph14e/electricmotor.htm
Other Relevant Programs Available from VEA
DC Electricity - Discovery and Developments
The Path to Nuclear Fission - The Story of Lise Meitner and Otto Hahn
Electronics - Transport, the Electronic Future - The Electronics Design in the Jaguar X350
A Study of Magnets
Magnetism
Please visit our website for more relevant programs www.veavideo.com
VEA – Bringing Learning to Life
2
DC Motors
Student Worksheet:
Before Viewing the Program
1.
Use some simple magnets (bar, horseshoe etc), plastic sheets and iron filings to look at the
magnetic field surrounding these magnets.
2.
Suspend a bar magnet and allow it to swing freely to either decide which end is the North
seeking (N-pole) or confirm the given N-pole.
3.
Investigate the effect of bar magnets on mapping compasses.
4.
Set up a simple copper wire connected to a battery (DC voltage!) and check the effect of a bar
magnet on this when there is current flowing or when there is no current present.
5.
Use an internet search to look for experiments by Oersted, Faraday.
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DC Motors
While Viewing the Program
1.
Explain the basic difference between a DC and an AC power supply.
2.
Magnetic field lines that are further apart indicate a
3.
Name three magnetic materials:
4.
Magnetic field lines travel from the
5.
Faraday imagined magnetic field lines as “lines of
6.
What rule gives the direction of the magnetic field for a current carrying wire?
magnetic field.
pole to the
“ or as
The
7.
rule.
The thumb should point in the direction of the conventional current which always travels
towards the
8.
terminal of the battery or power supply.
What rule gives the direction of the force on a current carrying wire placed in a magnetic field?
The
9.
pole.
rule.
Label the following diagram according to the rule in Question 8.
10. The diagram below shows a rod of length 0.15m carrying a current of 0.75A in a magnetic
field of 0.2T. Calculate the force acting on the rod and show the direction of this force by an
arrow on the diagram.
S
N
I
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DC Motors
11. What defines “useful” motion?
12. Why didn’t the ends of the current carrying loop in the motor contribute to the rotation of the
armature?
13. What is the name of the device that reverses the direction of the current in a DC motor every
½ turn?
14. What is the effect on the performance of the DC motor of multiple loops of wire wound on the
armature?
15. Give three ways that a DC motor can be made more efficient:
16. On the following diagram of a basic DC electric motor label: the axle, the brushes, the
commutator, the armature, the magnets, the current carrying loops.
17. Name a simple material that is commonly used for “brushes” in a commercial DC motor.
18. What performs the role of the “commutator” in a brushless DC motor?
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DC Motors
After Viewing the Program
A Note to Teachers:
There are a number of different commercially available DC motor kits that are relatively
inexpensive to purchase as a class set and are also re-useable. Students really enjoy making a small
model DC motor (especially if it runs!) and can get a lot from the experience.
The “Nuffield Practical Physics” site is one possible source of further information about suppliers
of the motor kit used in this program.
http://www.practicalphysics.org/go/Default.html;jsessionid=a-5yMQXEneG-
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