JEE Main 2026 — Jan 23, Shift 2 — Physics solution

JEE Main2026Jan 23, Shift 2Physics

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 ______.

A
1.45
B
1.16
C
1.75
D
1.55

Solution

Standard derivation: $\frac{ε _{1}}{ε _{2}} = \frac{ℓ _{1}}{ℓ _{2}}$ , so

$\frac{Δ y}{y} = \frac{Δ ℓ _{1}}{ℓ _{1}} + \frac{Δ ℓ _{2}}{ℓ _{2}} = \frac{1}{200} + \frac{1}{150} = \frac{3 + 4}{600} = \frac{7}{600}$ .

Percentage error $= \frac{7}{600} \times 100 \approx 1.16%$ .

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