As shown in the figure, a potentiometer wire of resistance 20 Ω and length 300 cm is connected with resistance box (R.B.) and a standard cell of emf 4 V. For a resistance ' R ' of resistance box introduced into the circuit, the null point for a cell of 20 mV is found to be 60 cm. The value of ' R ' is Ω.

Question

As shown in the figure, a potentiometer wire of resistance 20 Ω and length 300 cm is connected with resistance box (R.B.) and a standard cell of emf 4 V. For a resistance ' R ' of resistance box introduced into the circuit, the null point for a cell of 20 mV is found to be 60 cm. The value of ' R ' is Ω. (A)  (B)  (C)  (D)

Tardigrade Admin · Accepted Answer

E =( AC / AB )(V A - V B ) ∴ 20 × 10-3=(60/300) × (4 × 20/ R +20) ∴ R =780 Lambda

E=ABAC​(VA​−VB​) ∴20×10−3=30060​×R+204×20​ ∴R=780Λ

$E = \frac{A C}{A B} (V_{A} - V_{B})$
$∴ 20 \times 1 0^{- 3} = \frac{60}{300} \times \frac{4 \times 20}{R + 20}$
$∴ R = 780Λ$