Question

While performing the galvanometer experiment using half deflection method, a student got almost the same value for S, every time, whatever be the value of R he had set in the (high value) resistance box. This is because

(1) The resistance box in which S is put is faulty

(2) Resistance G is very low

(3) In half–deflection method, current gets divided between G and S and R is very high

(4) The internal resistance of the d.c source varies with current flow

Answer 1

(3) In half–deflection method, current gets divided between G and S and R is very high

Here, the galvanometer is a very sensitive device. The current flowing in it should be very low. So R should be quite high. 

The formula for G is

Since R is large, (R-S) is almost equal to R.

This shows that, G ≈ RS/R ≈ S