1. Chapter 20 Electromagnetic Induction

2. Electricity and magnetism Generators, motors, and transformers

3. Current Previously, we said three things were required for a current to flow in a circuit: 1.Potential difference 2.Closed circuit 3.Charges free to move

4. Electromagnetic Induction electromagnetic induction = the process of creating a current in a circuit loop by changing the magnetic field that passes through the circuit (Inducing an emf)

5. Linear Induction Flashlight / Faraday Flashlight / “Shake Flashlight”

7. Lenz’s Law Lenz’s Law describes the rule for finding the direction of the induced current: Note: the field of the induced current does not oppose the applied field, but the change in the applied field (so that the total field strength remains constant). The magnetic field of the induced current is in a direction to produce a field that opposes the change causing it.

8. Circuit is moved into the magnetic field

9. Circuit is rotated in the magnetic field

10. Intensity of the magnetic field is varied

12. Magnetic Flux (magnetic field) (surface area) magnetic flux = (cosine of the angle between B and the normal to the plane of the loop)

13. Faraday’s Law of Magnetic Induction

14. Practice A circuit is stretched over a period of 0.25 seconds in a magnetic field of 0.050 T. The circuit dimensions change from 4.0 m x 4.0 m to 2.0 m x 6.0 m, as shown below. Determine the emf induced in the circuit. start end 4.0 m 6.0 m 2.0 m

15. Faraday’s Law of Magnetic Induction For multiple loops, N = the number of loops in the circuit

16. Practice A coil with 25 turns of wire is wrapped around a hollow tube with an area of 1.8 m 2. Each turn has the same area as the tube. A uniform magnetic field is applied at a right angle to the plane of the coil. If the field increases uniformly from 0.00 T to 0.55 T in 0.85 s, find the magnitude of the induced emf in the coil. If the resistance in the coil is 2.5 Ω, find the magnitude and direction of the induced current in the coil.