Question

In a potentiometer experiment, the balancing length for a cell was found to be 1.20 m. Now, a resistance of
10 Q is connected across the terminals of this cell and the balancing length becomes 80 cm. The internal
resistance of this cell is.
(1) 20
(2) 50
(3) 1.52
(4) 15.​

Answer 1

Explanation:

Let us Consider a cell of emf E and balancing length l1

E=kl

1

potential difference is balanced by length l

2

.

V=kl

2

Internal resistance of the cell

r=(

V

E−V

)R=(

V

E

−1)R=(

l

2

l

1

−1)R

=(

560−60

560

−1)10=(

50

56

−1)10

=

5

6

=1.2Ω.