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 .,

MARKS App · Accepted Answer

Given here, l = 300 cm , R w = 20 Ω and ε = 4 V . Using the relation, E 2 = l 1 l 2 E 1 , we have E = A C A B V A - V B ∴ 20 × 10 - 3 = 60 300 × 4 × 20 R + 20 ⇒ 5 × 10 - 3 = 4 R + 20 ∴ R = 780 Ω

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