Physics 271L Experiment 8

Lenz's Law and Faraday's Law

[ Exercise 2 | Exercise 3 ]

In order to understand the experiments you must know the following facts.

• (a) Outside a magnet, is directed from the North to the South pole.
• (b) The windings of the coils are clockwise, when viewed from the clear plastic face.
• (c) Positive current into the (+) terminal of the galvanometer causes a deflection to the right (a positive deflection).

1. Construct the circuit in Fig. 1, using the many-turn coil. Answer questions (a) -> (e) first, then do step (f) to see if your predictions were correct.

• (a) If the N pole of the bar magnet is brought up to the clear face of the coil, what is the direction of through the center of the coil and how is changing?
• (b) According to Lenz' Law this will induce a current which will oppose the change in . Will this current be CW (clockwise) or CCW ?
• (c) Will this cause a positive or negative deflection on the galvanometer?
• (d) If you hold the bar magnet still at the face of the coil, will there be a flux through the coil? _______

  Will there be an induced current? If so, will it be CW or CCW ? If not, why not?

• (e) As you remove the magnet, how will the flux be changing?______

  Will the direction of the induced current be CW or CCW ?_________

  What should be the direction of the galvanometer deflection?________

• (f) Bring the N pole up to the center of the clear coil face. What is the galvanometer deflection? __________

  Hold the coil very still (rest it on a book, if necessary). What is the galvanometer deflection? ________

  Remove the magnet. What is the galvanometer deflection? ________

  (If your observations do not agree with your predictions ask the lab instructor to go over steps (a) -> (e) with you.)

• (g) What should the deflections be as you bring the S pole up to the clear coil face and then remove it? Try it and record the deflections.
• (h) Now use the few-turn coil and do (f) again for this new coil. Note the magnitude of deflections as compared to the many-turn coil. Do the directions and magnitude of deflection correspond for the two coils?

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