1. Workshop: Using Visualization in Teaching Introductory E&M AAPT National Summer Meeting, Edmonton, Alberta, Canada. Organizers: John Belcher, Peter Dourmashkin, Carolann Koleci, Sahana Murthy

2. Faraday’s Law Presentation Materials

3. MIT Class: Faraday’s Law
Week 9, Day 2
MIT Class: Faraday’s Law
Class 21

4. Fourth (Final) Maxwell’s Equation Underpinning of Much Technology
Faraday’s Law
Fourth (Final) Maxwell’s Equation
Underpinning of Much Technology

5. Demonstration: Falling Magnet

6. Magnet Falling Through a Ring
Falling magnet slows as it approaches a copper ring which has been immersed in liquid nitrogen.

7. Demonstration: Jumping Rings

8. Jumping Ring
An aluminum ring jumps into the air when the solenoid beneath it is energized

9. What is Going On?
It looks as though the conducting loops have current in them (they behave like magnetic dipoles) even though they aren’t hooked up

10. Faraday’s Law Applets Discovery

11. Faraday’s Law Applets Discovery Activity

12. Demonstration: Induction

13. Electromagnetic Induction

14. Faraday’s Law of Induction
A changing magnetic flux induces an EMF

15. Looks like potential. It’s a “driving force” for current
What is EMF?
Looks like potential. It’s a “driving force” for current

16. Faraday’s Law of Induction
A changing magnetic flux induces an EMF, a curling E field

17. Magnetic Flux Thru Wire Loop
Analogous to Electric Flux (Gauss’ Law)
(1) Uniform B
(2) Non-Uniform B

18. Minus Sign? Lenz’s Law
Induced EMF is in direction that opposes the change in flux that caused it

19. Faraday’s Law of Induction
Week 9, Day 2
Faraday’s Law of Induction
Changing magnetic flux induces an EMF
Lenz: Induction opposes change
Class 21

20. Ways to Induce EMF Quantities which can vary with time: Magnitude of B
Area A enclosed by the loop
Angle q between B and loop normal

21. Group Discussion: Magnet Falling Through a Ring
Falling magnet slows as it approaches a copper ring which has been immersed in liquid nitrogen.

22. Magnet Falling Through a Ring
Week 9, Day 2
Magnet Falling Through a Ring
Falling magnet slows as it approaches a copper ring which has been immersed in liquid nitrogen.
Class 21

23. Example: Magnitude of B Magnet Falling Through a Ring
Week 9, Day 2
Example: Magnitude of B Magnet Falling Through a Ring
Falling magnet approaches a copper ring
or Copper Ring approaches Magnet
Class 21

24. As ring approaches, what happens to flux?
Week 9, Day 2
Moving Towards Dipole
Move ring down
As ring approaches, what happens to flux?
Flux up increases
Class 21

25. PRS Question: Faraday’s Law
Week 9, Day 2
PRS Question: Faraday’s Law
Class 21

26. PRS: Faraday’s Law: Loop
Week 9, Day 2
PRS: Faraday’s Law: Loop
:00
A coil moves up from underneath a magnet with its north pole pointing upward. The current in the coil and the force on the coil:
Current clockwise; force up
Current counterclockwise; force up
Current clockwise; force down
Current counterclockwise; force down
Class 22

27. PRS Answer: Faraday’s Law: Loop
Week 9, Day 2
PRS Answer: Faraday’s Law: Loop
Answer: 3. Current is clockwise; force is down
The clockwise current creates a self-field downward, trying to offset the increase of magnetic flux through the coil as it moves upward into stronger fields (Lenz’s Law).
The I dl x B force on the coil is a force which is trying to keep the flux through the coil from increasing by slowing it down (Lenz’s Law again).
Class 22

28. PRS Question: Loop in Uniform Field
Week 9, Day 2
PRS Question: Loop in Uniform Field
Class 21

29. PRS: Loop in Uniform Field
Week 09, Day 1 v
Bout
A rectangular wire loop is pulled thru a uniform B field penetrating its top half, as shown. The induced current and the force and torque on the loop are:
Current CW, Force Left, No Torque
Current CW, No Force, Torque Rotates CCW
Current CCW, Force Left, No Torque
Current CCW, No Force, Torque Rotates CCW
No current, force or torque
Class 20

30. PRS Answer: Loop in Uniform Field
Week 09, Day 1
PRS Answer: Loop in Uniform Field v
Bout
Answer: 5. No current, force or torque
The motion does not change the magnetic flux, so Faraday’s Law says there is no induced EMF, or current, or force, or torque.
Of course, if we were pulling at all up or down there would be a force to oppose that motion.
Class 20

31. Group Problem: Changing Area
Conducting rod pulled along two conducting rails in a uniform magnetic field B at constant velocity v
Direction of induced current?
Direction of resultant force?
Magnitude of EMF?
Magnitude of current?
Power externally supplied to move at constant v?

32. Changing Angle