08-16-2017, 10:01 PM
In electronics, the Carey Foster bridge is a bridge circuit used to measure low resistances, or to measure small differences between two large resistances. It was invented by Carey Foster as a variant on the Wheatstone bridge.You may be familiar with the post office box and the meter bridge, which also
work on the same principle as Wheatstone s bridge. In the meter bridge, two of
the resistors, R and S, say, are replaced by a one meter length of resistance wire,
with uniform cross-sectional area fixed on a meter scale. Point D is an electrical
contact that can be moved along the wire, thus varying the magnitudes of
resistances R and S. The Carey Foster bridge is a modified form of the meter
bridge in which the effective length of the wire is considerably increased by
connecting a resistance in series with each end of the wire. This increases the
accuracy of the bridge.
While performing this experiment, you will balance the Carey Foster bridge by a
null deflection method using a galvanometer. You will first determine the
resistance per unit length of the material used for the bridge wire, and will then
determine the value of an unknown resistance.
