Question

Write the principle of working of a metre bridge

Answer 1

Metre bridge follows the principle of Wheatstone bridge. Wheatstone bridge principle states that if four resistance P, Q, R and S are arranged to form a bridge as shown below with a cell ε and one way K between the points A and C and a galvanometer G between the points B and D, then on closing K, if galvanometer shows no deflection, the bridge is balanced.

Then, `P/Q=R/S`

P = resistance of the length l cm of the wire AD = lr
and Q = resistance of the length (100 - l) cm of the wire DC = (100 - l) × r.
where,​ r is the resistance per unit length of the wire.