metre-bridge-current electricity

 

Metre Bridge

Above figure shows the diagram of meter bridge. It consists of a ---------

one-meter wire of uniform cross section fixed on a wooden table with a metre scale.

Two L shaped metallic strips separated by a single metallic strip,

an unknown resistance X connected in left gap and

a resistance box connected in right gap,

galvanometer connected to the central tap and other terminal is connected to the jockey J.

A cell of emf ε along with a key and a rheostat are connected between the points A and B.

Working:

A suitable resistance R is selected from resistance box. The jockey is brought in contact with AB at various points on the wire AB and the balance point (null point), D, is obtained. The galvanometer shows no deflection when the jockey is at the balance point.

If l_x and l_R are the respective lengths of the wire between AD and DC respectively, then using the conditions for balance we get

where R_AD and R_DB are resistance of the wire of the parts AD and DB.

The resistance R_AD and R_DB are given as

Thus if we know the value of R, l_x and l_R then we can determine the value of unknown resistance.