This document describes Whetstone's bridge circuit used to measure an unknown resistance. It notes potential errors from non-uniform wire thickness or contact resistance, and how they can be minimized by taking multiple readings and calculating the average. It also provides the formula to calculate the resistance of a galvanometer used to read the null point in the circuit. Finally, it includes a multiple choice question testing understanding of the equivalent resistance in the Whetstone's bridge circuit.

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Whetstone’s Network

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1 3
2 4
R R
R R

Whetstone’s metrebridge
x
x B
R
l
R R
l
 
Errors
 The wire may not be uniformly thick.
 The contact resistance between the plates and
wires at A and C.
Minimization of Errors
 Two sets of 3 readings are taken by interchanging
positions of RX and R B, and average is calculated

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 The resistance RB is adjusted such that the null
point is obtained at the middle of AB.
Resistance of Galvanometer
Here, instead of null point equal deflection point is
obtained
The resistance of galvanometer is given by
g
B
R
l
G R
l
 

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Multiple Choice Questions 1. Each of the resistance in the network shown in the figure is equal to R. The resistance between the terminals A and B is (a) 3R (b) R (c) 5R (d) 6R

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Ans : (b) R The equivalent circuit of the given network is a balanced wheatstone’s network as shown in the figure No current will flow through the branch LK ∴ Resistance in the branch ALB = 2R and resistance in the branch AKB = 2R. As they are in parallel, their effective resistance = R

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