This consists of a circuit of four resistors arranged as shown. They are sensitive galvanometer, a cell and a switch
When the four resistors, PQRS are adjusted, no current flows even with switch B closed and no defection on the galvanometer.
Current through P =Current through Q
Current through R = Current through s
Potential difference across P = Potential difference across R
Potential difference cross Q = Potential difference across S
I1 x P = I2 x P
I1 x Q = I2 x S
∴ \( \frac{P}{Q} = \frac{R}{S} \)
If R is an unknown resistance, it can easily be calculated from the relation
R = \( \frac{PS}{Q} \)
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