Circuit for the measurement of resistance by potentiometer is shown in Figure. The galvanometer is first connected at point and zero deflection is observed at length = 10 cm. In second case, it is connected at point and zero deflection is observed at a length 30 cm from , then the unknown resistance is
2 R
R/2
R/3
3 R
In potentiometer wire, potential difference is directly proportional to length, let the potential drop of unit length of a potentiometer wire be k

For zero deflection, the current will flow independently in two circles:
Subtracting Eq. (ii) from Eq. (i), we get
Dividing Eq. (i) by Eq. (ii), we have