Question

II. TESTING EXPERIMENT: IS MOTION NECESSARY FOR INDUCING ELECTRIC CURRENT IN A COIL NOT CONNECTED TO A BATTERY? The goal of this experiment to test the rule you invented in Experiment I. Available equipment: Computer with internet connection a) In this experiment you have two coils: one (coil A on the left) connected to a large galvanometer and one (coil B on the right) connected to a power supply and current indicator (another small galvanometer). Use the rule you invented in Experiment I to predict what happens to the reading of the galvanometer connected to coil when two coils are positioned next to each other as shown in the photo below. For each prediction, be as specific as you can. Sketch a rough I vs. t graph for what you think the galvanometer will show. IIIIII Experiment # Written Description Prediction Based on Rule Outcome 1 Coil B is moved away from coil A, then moved back. 2 Coil A is moved away from coil B, then moved back. 3 Coil B is moved perpendicularly away from coil A, then moved back into place. Coil B is suddenly disconnected from its power supply, then reconnected after a few seconds. b) Once you have made your predictions watch this video and record the outcome of each experiment. Be as specific as you can in recording the outcomes. c) Did the outcomes of the experiments match your predictions? If not, how should you revise your rule?

Answer 1

In the given experimental setup, the Faradays law of induced emf/current and Lenz law is verified.

The two coils through which current passes, creates a magnetic field according to the right hand thumb rule, and the magnet is moved towards or away from another magnet, the change in the magnetic field causes a change in the flux given by $\phi$ =B. dA, where dA=elementary area of the loop. The changing mangnetic flux creates an emf given by Faraday's equation emf=-d$\phi$/dt, which according to the Lenz law is opposite to the cause producing it and is reflected the galvanometers connected to the coil.

1) When coil B is moved away from coil A, emf us produced due to changing magnetic flux. When it is moved back in the opposite direction, the flux reverses its direction and hence the emf also changes accordingly. This is seen in the galvanometer connected to A.

2) When coil A is moved in the same fashion, the same changes occur and that is reflected in the galvanometer connected to B.

3) When coil B is moved perpendicular to A, the magnetic field lines do not change in B and hence, no emf is produced, and the galvanometer doesn't deflect.

4) When coil B is suddenly disconnected from the power supply, the magnetic flyx reduces at first, creating an emf in A. When it is turned off, the galvanometer doesn't delfect. On again turning on the power supply, emf is induced in the opposite direction since magnetic flux increases, and hence galvanometer deflects in the direction opposite to before.