Question

For the circuit shown here, the galvanometer deflection equals (i) 15 divisons when the key K₂ is kept open and (ii) 3 divisions when key K₂ is closed. The resistance of this galvanometer is (nearly)

(1) 60Ω

(2) 64Ω

(3) 68Ω

(4) 75Ω

Answer 1

(2) 64Ω

With the key K₂ open, the current, through the galvanometer, is

When the key K₂ is closed, the total resistance of the circuit equals \(\left[R+\frac{GS}{(G+S)} \right].\) Hence the current, through the galvanometer, is