02-05-2017, 09:45 AM
In electronics, the Carey Foster Bridge is a bridge circuit used to measure low resistances, or to measure small differences between two large resistors. It was invented by Carey Foster as a variant on the Wheatstone Bridge. He first described it in his 1872 paper "On a Modified Form of the Wheatstone Bridge, and Methods of Small Resistance Measurement" (Telegraph Engineer's Journal, 1872-1873, 1, 196).
Viva questions and answers
Q. What is resistance?
A. Resistance R = V \ I, where V is the potential difference applied through the wire and I is the current flowing through it due to the potential difference.
Q. What is specific resistance?
A. Specific resistance of a material is the resistance of one centimeter of length of wire whose cross-sectional area is one square centimeter.
Q. What is the effect of temperature on resistance?
A. The resistance increases with increasing temperature of the wire material.
Q. In what materials does the resistance decrease with increasing temperature?
A.In Semiconductors
Q. If the cable radius doubles, will the specific resistance change?
The specific resistance of A. is independent of the length or radius of the wire which depends only on the material of the wire.
Q. Why does the resistance wire wire bend before it rolls over the coil?
A.To avoid inductive effects. The direction of the current in one wire is opposite to the other, reason why the total flow is always zero.
Q. What is the beginning of Carey Foster Bridge?
A. The position of the null point changes in the wire when the resistance is connected in the outer spaces is exchanged. The difference in the value of the resistance is equal to the resistances of the differences of the bridge cable, ie, (L-1).
Q. What is the beginning of Wheatstone Bridge?
A. When the four resistors P, Q, R, S in the four arms of the Wheatstone bridge are such that there is no deflection in the galvanometer, we have:
P / Q = R / S
Q. When is the Carey Foster Bridge more sensitive?
A. It is more sensitive when P, Q, R, S are the same or of the same order.
Q. Why is the resistance for the internal relationship arms the same?
A. For greater sensitivity and accuracy.