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JEE Main 2022 · 27 Jun · Shift 1, Physics question 55

A cell, shunted by a 8 Ω8\ \Omega resistance, is balanced across a potentiometer wire of length 3 m. The balancing length is 2 m when the cell is shunted by 4 Ω4\ \Omega resistance. The value of internal resistance of the cell will be ______ Ω\Omega.

Answer and worked solution

Official answer: 8

Terminal voltage ∝ balancing length. 8/(8+r)4/(4+r)=32\dfrac{8/(8+r)}{4/(4+r)}=\dfrac32, i.e. 4(4+r)=3(8+r)4(4+r)=3(8+r).

So r=8 Ωr=8\ \Omega.

Answer: 8

Topics:PotentiometerEMF and internal resistance
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