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Current Electricity

JEE Main level, single correct, medium

309 of 380

Question 309 of 380

In a metre bridge experiment null point is obtained at $20 \mathrm{~cm}$ from one end of the wire when resistance $X$ is balanced against another resistance $Y$ . If $X \lt Y$ , then where will be the new position of the null point from the same end, if one decides to balance a resistance of $4 X$ against Y?

Show answer and solution

Answer: (A) $50 \mathrm{~cm}$

We have from meter bridge experiment,

\frac{\mathrm{R}_1}{\mathrm{R}_2}=\frac{\ell_1}{\ell_2}

, where

\ell_2=\left(100-\ell_1\right) \mathrm{cm}

In the first case,

X / Y=20 / 80

In the second case

\frac{4 X}{Y}=\frac{\ell}{100-\ell}

\ell=50 \mathrm{~cm}

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JEE Main 2025 Apr 2 Shift 1 question paper

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