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Fig 31-CO, p.967

Learn about Faraday's Law of Induction and explore its applications through experiments in the PHET lab. Understand the effects of magnet polarity, motion speed, coil turns, and area on the observed voltage. Explore Lenz's Law, generators, and motors.

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Fig 31-CO, p.967

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  1. Fig 31-CO, p.967

  2. p.968

  3. Ch 31 Faraday’s Law 31.1 Faraday’s Law of Induction  = -NdB/dt

  4. CT1: In Faraday’s Electromagnetic Lab (PHET), I redo the experiment with the bar magnet and pick-up coil, but with the polarity of the bar magnet reversed. As before, with the bar magnet to the left of the pick-up coil, I first move the bar magnet towards the pick-up coil. Second I pull the bar magnet away from the pick-up coil. What will happen to the signs of the observed voltage across the pick-up coil? • Both signs stay the same. • Both signs reverse. • The first sign reverses and the second sign stays the same. • The second sign reverses and the first sign stays the same.

  5. CT2: In Faraday’s Electromagnetic Lab (PHET), I redo the experiment with the bar magnet and pick-up coil, but pull the bar magnet away more rapidly. What will happen to the magnitude of the observed voltage across the pick-up coil? • The magnitude will stay the same. • The magnitude will decrease. • The magnitude will increase.

  6. CT3: In Faraday’s Electromagnetic Lab (PHET), I redo the experiment with the bar magnet and pick-up coil, but with the number of turns in the pick-up coil increased. What will happen to the magnitude of the observed voltage across the pick-up coil? • The magnitude will stay the same. • The magnitude will decrease. • The magnitude will increase.

  7. CT4: In Faraday’s Electromagnetic Lab (PHET), I redo the experiment with the bar magnet and pick-up coil, but with the area of the the pick-up coil increased. What will happen to the magnitude of the observed voltage across the pick-up coil? • The magnitude will stay the same. • The magnitude will decrease. • The magnitude will increase.

  8. CT5: In Faraday’s Electromagnetic Lab (PHET), I put a pick-up coil near the electromagnet. When will the pick-p coil will register a voltage? • The current in the electromagnet is DC. • The current in the electromagnet is AC. • The current in the electromagnet is either DC or AC. • Not in any case.

  9. CT6: In Faraday’s Electromagnetic Lab (PHET), I have an electromagnet and pick-up coil (transformer). If I increase the magnitude of the AC current, the magnitude of the voltage in the pick-up coil will • stay the same. • decrease. • increase.

  10. Ch 31 Faraday’s Law 31.1 Faraday’s Law of Induction  = -NdB/dt B = B·dA B = BA if B is constant and along dA P31.7 (p.888) 

  11. P31.67 (p.896) infinitesimal area element of width dx and length L at x x

  12. Ch 31 Faraday’s Law 31.2 Motional emf V = Blv

  13. CT7: Knowing that the terminal velocity is determined by zero acceleration when FB = ILB = mg, how does vT depend on mg? Recall I = V/R. • independent of mg • mg • mg2 • 1/mg • 1/(mg)2

  14. CT8: Knowing that the terminal velocity is determined by zero acceleration when FB = ILB = mg, how does vT depend on R? Recall I = V/R. • independent of R • R • R2 • 1/R • 1/R2

  15. P31.43 (p.893)  = -dB/dt = -d(BA)/dt = -d(Bwy)/dt = -Bwdy/dt = -Bwv (cw) I = /R = Bwv/R FB I y

  16. Ch 31 Faraday’s Law 31.3 Lenz’s Law An induced current creates a magnetic field that opposes the change in magnetic flux that created it. Alternatively, the induced magnetic field tends to maintain the magnetic flux by opposing the change in flux.

  17. Fig 31-14a, p.978

  18. Fig 31-14c, p.978

  19. CT9: A magnet is released at the top of each copper tube – one without a slit and one with. • The magnet in the tube without the slit reaches the bottom first.B. The magnet in the tube with the slit reaches the bottom first.C. The magnets in both tubes reach the bottom at the same time.

  20. CT10: For the jumping ring demo, if I use a ring that is twice as thick and all else is equal, the ring will • not move • jump approximately half as high • jump approximately twice as high • jump approximately the same height

  21. CT11: For the jumping ring demo, if I use a ring that is has a slot cut along its length and all else is equal, the ring will • not move • jump approximately half as high • jump approximately twice as high • jump approximately the same height

  22. x P31.28 (p.891) • CT12-15 • in • out • right • left • up • down

  23. Ch 31 Faraday’s Law 31.4 Induced emf and Electric Fields E·ds = -dB/dt P31.33 (p.891) 

  24. CT16: In figure (a), a solenoid produces a magnetic field whose strength increases into the plane of the page. An induced emf is established in a conducting loop surrounding the solenoid, and this emf lights bulbs A and B. In figure (b), points P and Q are shorted. After the short is inserted, • bulb A goes out; bulb B gets brighter. • bulb B goes out; bulb A gets brighter. • bulb A goes out; bulb B gets dimmer. • bulb B goes out; bulb A gets dimmer. • both bulbs go out. • none of the above

  25. Ch 31 Faraday’s Law 31.4 Generators and Motors

  26. P31.54 (p.999) P31.64 (p.896)

  27. Polling Question: How many hours per week to you spend outside of class on average for PHYS151? • 2 or less • 3 • 4 • 5 • 6 • 7 • 8 or more

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