In a metre bridge experiment, the balancing length from the left end is found to be $25 \mathrm{~cm}

Question

In a metre bridge experiment, the balancing length from the left end is found to be $25 \mathrm{~cm}$. If a standard resistance of $3 \Omega$ is kept in the right gap, the value of the unknown resistance in the left gap is

Professor PC Thomas Classes · Answer

(c) : A metre bridge operates on the principle of a Wheatstone bridge. The condition for balance is $\frac{P}{Q} = \frac{l}{100 - l}$. Here, $l = 25 \mathrm{~cm}$, and the right gap resistance $Q = 3 \Omega$. Therefore, $\frac{P}{3} = \frac{25}{100 - 25} = \frac{25}{75} = \frac{1}{3}$. Solving for $P$, we get $P = 3 	imes \frac{1}{3} = 1 \Omega$.