Question

In the potentiometer circuit shown in figure, the balance length AJ = 60 cm when switch S is open. When switch S is closed and the value of R = 5 Ω, the balance length AJ' = 50 cm. What is the internal resistance of cell C' ?
(A) 0.5 Ω
(B) 1 Ω
(C) 1.5 Ω
(D) 0.1 Ω

Answer 1

the relation we have to use , $\bf{r=\frac{l_1-l_2}{l_2}R}$

where r is the internal resistance , R is resistance of connected resistor, l₁ and l₂ are balance lengths initial and final.

Here, R = 5Ω , l₁ = 60cm, l₂ = 50cm

so, r =  (60 - 50)/50 × 5Ω = 1Ω

hence, option (B) is correct.