Question

A length of 150 cm of a potentiometer wire is required to balance the emf of a cell. When a 5 resistor is connected across the terminals of the cell, the length required for balance is 125 cm. The internal resistance of the cell is

Answer 1

Length of the potentiometer wirel

1

=150cm

Resistance R=5Ω

balancing length is obtained at l

2

=125cm

Internal resistance r=?

we have,

r=R[

l

2

l

1

−1]

=5[

125

150

−1]

=5[

125

25

]

=1Ω