Meter Bridge

Class XII - Physics

 

Meter Bridge

It is an electric device used for measuring the resistance of a unknown substance.

Construction :-

Meter bridge consist of a uniform wire of length 100 cm stretched on a wooden strand. The ends of the wire are joined to thick copper strips at A and B. Meter scale is fixed on the board parallel to the wire. Two gaps are left in the copper strips to join in which one gap is joined to the resistance box whereas other gap is joined with unknown resistance X. A cell having emf 'E' supplies current through the circuit.

Principle :-

Meter bridge works on the principle of wheatstone bridge.

i.e.

 

Working :-

When current is passed through the circuit, jockey is slided over the wire to obtain the balanced condition and at point C in the given figure the galvanometer shows no deflection or balanced condition is obtained. Let the length between A and C be 'l' ,then the distance between B & C becomes (100 - l ). Now, let P be the resistance of the wire AC and Q be the resistance of the wire BC.

Now, we know that,

P α l [ P is directly proportional to the length of wire AC ]

Q α (100 – l) [Q is directly proportional to the length of the wire BC]

From Wheatstone Bridge Principle,