(a) Write the principle of working of a metre bridge.
(b) In a metre bridge, the balance point is found at a distance l₁ with resistances R and S as shown in the figure.

An unknown resistance X is now connected in parallel to the resistance S and the balance point is found at a distance l₂. Obtain a formula for X in terms of l₁, l₂ and S.

(a) In a metre bridge, the balance point is found at a distance l1 with resistance R and S as shown in the figure.
Meter bridge works on the principle of balanced Wheatstone bridge i.e., when the bridge is balanced, R₁R₂ = R₃R₄
Where R₁, R₂, R₃ and R₄ are the resistances connected in four arms of Wheatstone's

(b) In meter bridge balance condition is given by
When X is connected in parallel with S equivalent resistance in that arm.

New balanced condition is given by