Question

Ramesh performed an experiment to determine an unknown resistance R using the circuit shown in the figure below. X is a resistance box and PQ is a 100 cm potentiometer wire. He closed the key and inserted X = 1 Ω, 2 Ω and recorded the null point (l) corresponding to different values of X.

1. Identify the principle involved in calculating R.
2. Write down a relation required to calculate the resistance R in terms of X and (l).

Answer 1

a. Wheatstone Bridge Principle

b. At balance (null point) in a meter bridge, the ratio of the resistances in the two gaps equals the ratio of the lengths of the wire segments.

`X/R = l/(100 - l)`

R = `(X(100 - l))/l`