Question

Why Carey Foster's bridge is so sensitive ?

Answer 1

Carey Foster's bridge

1. The sensitivity of Carey Foster's bridge is proportional to the length of wire used in the bridge.
2. It uses the same fundamental principle as the Wheatstone bridge, it is balanced when the two pairs of resistances connected to the galvanometer have the same ratio.
3. It is most sensitive when all resistances are of the same order.
4. In the Carey Foster bridge, two resistances are of the same order, and the unknown and known resistances are of the same order.
5. A Carey Foster bridge diagram is shown at the right, where P and Q are resistances of nearly equal value, Y is the known resistance, and X is the unknown resistance.

So it is considered to be very sensitive and can be used to measure the tiniest decimal change in resistance.