JEE Main 2022 · 28 Jul · Shift 1 · Physics Q55

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PhysicsInteger+4 / -1Question 55 of 90

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.

Potentiometer wire AB fed by a 4 V cell through a key and resistance box R; a 20 mV cell and galvanometer G connected from A to the jockey.

Your answer

Answer and worked solution

Official answer: 780

Gradient. 20 mV over 60 cm means 0.1 V across the whole wire, so $I=\frac{0.1}{20}=5$ mA.

Circuit. $4=0.005(20+R)$ , so $R=780$ Ω.

Answer: 780

Topics:Potentiometer

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JEE Main 2022 · 28 Jul · Shift 1, Physics question 55