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JEE Main 2026 (23 Jan, Shift 2) · Potentiometer

Potentiometer question from JEE Main 2026 (23 Jan, Shift 2)

Q15JEE Main 2026 · 23 JAN · SHIFT 2Medium

Potentiometer

To compare EMF of two cells using potentiometer the balancing lengths obtained are 200 cm and 150 cm. The least count of scale is 1 cm. The percentage error in the ratio of EMFs is ______

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Answer: (c)

$\dfrac{E_1}{E_2} = \dfrac{l_1}{l_2}$ , so the fractional errors add: $\dfrac{\Delta r}{r} = \dfrac{\Delta l_1}{l_1}+\dfrac{\Delta l_2}{l_2}$ .
With $\Delta l = 1$ cm: $\dfrac{1}{200}+\dfrac{1}{150} = 0.005+0.00667 = 0.01167$
Percentage error $= 1.17\%$
So the answer is (c) 1.17.

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