1. Chapter 20 Induced Voltages and Inductance
Induce emf and Magnetic flux
Faraday’s law of induction
Lenz’s law
Motional emf
Generators
Self-Inductance
RL circuits
Energy stored in a magnetic field

2. Michael Faraday 1791 – 1867 Great experimental scientist
Invented electric motor, generator and transformers
Discovered electromagnetic induction
Discovered laws of electrolysis

3. Faraday’s Experiment – Set Up
What is induced emf?
How is it produced?

4. Magnetic Flux What is magnetic flux? How do I calculate it?
What is the SI units?
Why the angle dependence?
Flux and B

5. Electromagnetic Induction – An Experiment
What is electromagnetic induction?
What is induced current?

6. Example
The quarter-circle loop shown in figure has an area of 15 cm2. A magnetic field, with B=0.16T exists in the +x direction. Find the flux through the loop in each orientation shown.

7. Example B a) n
plane
normal
20º B
20º
70º B
normal
20º
plane b) c)

8. Faraday’s Law and Electromagnetic Induction
What is Faraday’s law?
What is the formula?
What is the SI units?
How to change the flux?
What is Lenz’s law?

9. Example
As shown a metal rod makes contact with a partial circuit. The circuit is perpendicular to the magnetic field. Find the induced emf if the rod moves with velocity of v=2m/s. Assume L=0.5m

10. Lenz’ Law – Example

11. Example
See figures

12. Example
See figures

13. Applications of Faraday’s Law – Ground Fault Interrupters

14. Applications of Faraday’s Law – Apnea Monitor

15. Application of Faraday’s Law – Motional emf
What is motional emf?
How is it produced?
The force on charges
The potential difference

16. Motional emf in a Circuit
How do I calculate motional emf?
Motional emf and Battery
What is the resulting current?

17. Example
As shown, a metal rod makes contact with a partial circuit and completes the circuit. The circuit area is perpendicular to the magnetic field with B=0.15T. If the resistance of the total circuit is 3 ohm, how large a force is needed to move the rod as indicated with a speed of 2 m/s.

18. Lenz’ Law Revisited – Moving Bar Example
How do I calculate the direction of induced current?
One possibility

19. Lenz’ Law, Bar Example
Another possibility
Conservation of energy

20. Lenz’ Law – Moving Magnet Example
When applying Lenz’ Law, there are two magnetic fields to consider
The external changing magnetic field that induces the current in the loop
The magnetic field produced by the current in the loop

21. AC Generators
What is a generator?
How does it work?
Emf of the loop

22. DC Generators

23. Motors
What is a Motor?
Motors an Back

24. Joseph Henry 1797 – 1878 First director of the Smithsonian
First president of the Academy of Natural Science
First to produce an electric current with a magnetic field
Improved the design of the electro-magnetic and constructed a motor
Discovered self-inductance

25. Self-inductance What is self-inductance? How do I calculate it?
What are it SI units?
What is inductance?

26. Example
A coiled telephone cord has 70 turns, a cross-sectional diameter of 1.3 cm, and an unstrectched length of 60 cm. Determine an approximate value for the self-inductance of the unstretched cord.

27. Inductor and RL Circuit
What is an inductor?
How does it work in a circuit?
RL circuit
What is the time constant?
How do I find the current in the circuit?
What is the energy stored in the inductor?

28. Example For the circuit shown, determine Time constant
Current after one time constant
Change in potential at t=0 and t=first time constant
The rate of change of current after first time constant