Question

Describe the observation when the switch S is (i) closed suddenly, (ii) then closed, (iii) finally opened.

Answer 1

When the key is pressed it is observed that, the galvanometer shows a small momentary deflection and then returns to zero. When the key is released, the galvanometer again shows a small momentary deflection, but in opposite direction and then returns to zero. This phenomena is due to Electromagnetic induction discovered by Faraday, which states that it is the production of an electromotive force across a conductor when it is exposed to a varying magnetic field. Let us consider the cases one by one.
Case (i) closed suddenly: The Galvanometer needle shows a small momentary deflection and then returns to zero. Let us say that the deflection is towards the right.
Case (ii) then closed:
The Galvanometer shows no deflection because there is no change in the electric circuit.
Case (iii) finally opened
The Galvanometer shows a small momentary deflection in the opposite direction and then comes back to zero.