Explain how a low resistance is measured by a potentiometer
Measurement of resistance:
Let unknown resistor R is connected in series with a standard resistor S. The current through the circuit is controlled with the help of rheostat. A two-pole double throw switch is used.
When the switch is put at position 1-1’ the unknown resistance R is connected to the potentiometer circuit and the reading of the potentiometer is \(V_R\).
\(V_R\) =I.R ….. (1)
Now switch S is thrown to position 2-2’. This connects the standard resistor to the potentiometer.
\(V_S\)=I.S. ….. (2)
From (1) and (2), we get
\(\frac{V_R}{V_S}=\frac{R}{S}\)
Or, \( R=\ \frac{V_R}{V_S}S\)
Since the value of S is known, the value of R can be calculated.
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Fig.22(a)