1. Flux Faraday’s law Lenz’s law Examples Generator

2. Electromagnetic Induction
Magnetic Flux
If B is constant

3. Electromagnetic Induction

4. Electromagnetic Induction

5. Electromagnetic Induction
Faraday’s Law
Last time we ended class by dropping a magnet through a coil. Let’s do it again.
coil

6. Electromagnetic Induction
Faraday’s Law
This phenomena is called electromagnetic induction and is described by Faraday’s law. Write Faraday’s law.
In order to understand Faraday’s law we need to understand the concept of magnetic flux. Write the definition of magnetic flux.

7. Electromagnetic Induction
Faraday’s Law
The magnetic flux is exactly like the electric flux we studied in Gauss’s law. The flux is defined in terms of a vector area dA. Describe the magnitude and direction of this vector.
normal to area dA
The magnitude is the common area and the direction is normal to the area.

8. Electromagnetic Induction
Lenz’s Law
The direction of the emf and thus the current is given by Lenz’s law. The statement in bold in the center of page 789 is a statement of Lenz’s law. Use this to find the direction of the current. If you are looking down on the loop from above, is the current flowing clockwise or counter clockwise? Explain.

9. Electromagnetic Induction
Lenz’s Law
The magnetic is moving away from the coil so the magnetic field is decreasing, thus the current is in a direction to off-set the decrease.
The magnetic is moving toward the coil so the magnetic field is increasing, thus the current is in a direction to off-set the increase.

10. Electromagnetic Induction
Faraday’s Law

11. Electromagnetic Induction
Faraday’s Law
Does it make a difference if it is the magnetic moving or the coil? This was a major point in Einstein’s theory of relativity.

12. Electromagnetic Induction
Faraday’s Law
What about these two cases?

13. Electromagnetic Induction
Faraday’s Law

14. Electromagnetic Induction
Faraday’s Law
Show that when you integrate the emf, e with respect to time you get the average change in flux in time t.
Average value

15. Electromagnetic Induction
Problem
A circular wire loop with a radius of 20 cm. is in a constant magnetic field of 0.5 T .
What is the flux through
the loop if the normal to
the loop makes an angle
of 300 with the magnetic
field?
300
normal

16. Electromagnetic Induction
Problem
The magnetic field increases from 0.5 T to 2.5 T in 0.8 seconds. What is the average emf, e(t) induced in the loop.

17. Student Workbook

18. Student Workbook

19. Student Workbook

20. Student Workbook

21. Student Workbook

22. Student Workbook

23. Class Questions
Is there an induced current in this circuit? If so, what is its direction?
1. Yes, clockwise
2. Yes, counterclockwise
3. No

24. Class Questions
Is there an induced current in this circuit? If so, what is its direction?
1. Yes, clockwise
2. Yes, counterclockwise
3. No

25. Class Questions
A square loop of copper wire is pulled through a region of magnetic field. Rank in order, from strongest to weakest, the pulling forces that must be applied to keep the loop moving at constant speed.
1. F2 = F4 > F1 = F3
2. F3 > F2 = F4 > F1
3. F3 > F4 > F2 > F1
4. F4 > F2 > F1 = F3
5. F4 > F3 > F2 > F1

26. Class Questions
A square loop of copper wire is pulled through a region of magnetic field. Rank in order, from strongest to weakest, the pulling forces that must be applied to keep the loop moving at constant speed.
1. F2 = F4 > F1 = F3
2. F3 > F2 = F4 > F1
3. F3 > F4 > F2 > F1
4. F4 > F2 > F1 = F3
5. F4 > F3 > F2 > F1

27. Class Questions
A current-carrying wire is pulled away from a conducting loop in the direction shown. As the wire is moving, is there a cw current around the loop, a ccw current or no current?
1. There is a clockwise current around the loop.
2. There is a counterclockwise current around the loop.
3. There is no current around the loop.

28. Class Questions
A current-carrying wire is pulled away from a conducting loop in the direction shown. As the wire is moving, is there a cw current around the loop, a ccw current or no current?
1. There is a clockwise current around the loop.
2. There is a counterclockwise current around the loop.
3. There is no current around the loop.

29. Class Questions
A conducting loop is halfway into a magnetic field. Suppose the magnetic field begins to increase rapidly in strength. What happens to the loop?
1. The loop is pushed upward, toward the top of the page.
2. The loop is pushed downward, toward the bottom of the page.
3. The loop is pulled to the left, into the magnetic field.
4. The loop is pushed to the right, out of the magnetic field.
5. The tension is the wires increases but the loop does not move.

30. Class Questions
A conducting loop is halfway into a magnetic field. Suppose the magnetic field begins to increase rapidly in strength. What happens to the loop?
1. The loop is pushed upward, toward the top of the page.
2. The loop is pushed downward, toward the bottom of the page.
3. The loop is pulled to the left, into the magnetic field.
4. The loop is pushed to the right, out of the magnetic field.
5. The tension is the wires increases but the loop does not move.

31. Electromagnetic Induction
Example: Induction stove
The pan on the stove is heated by eddy currents produced by induction.
Would this stove work with a ceramic bowl?
Does the surface of the stove get hot?

32. Electromagnetic Induction
Application of Faraday’s Law
Generator

33. Electromagnetic Induction
Application of Faraday’s Law
Magnetic Recording

34. Electromagnetic Induction
The Most Important Point of Faraday’s Law
A changing magnetic field produces
or creates an electric field.
Two types of electric fields. One is created by charge and the other is created by a changing magnetic field.

35. Student Workbook