JEE Mains · Physics · STD 12 - Current electricity
- JEE Mains 2024
- Hard
- MCQ
In a metre-bridge when a resistance in the left gap is \(2\ \Omega\) and unknown resistance in the right gap, the balance length is found to be \(40\ \mathrm{cm}\). On shunting the unknown resistance with \(2\ \Omega\), the balance length changes by _______.
Pick an option to check your answer.
Answer & Solution
Correct Answer
(A) \(22.5 \mathrm{~cm}\)
Step-by-step Solution
Detailed explanation
First case \(\frac{2}{40}=\frac{X}{60} \Rightarrow X=3 \Omega\)
In second case \(X^{\prime}=\frac{2 \times 3}{2+3}=1.2 \Omega\)
\(\frac{2}{\ell}=\frac{1.2}{100-\ell}\)
\(200-2 \ell=1.2 \ell\)
\(\ell=\frac{200}{3.2}=62 . \mathrm{bm}\)
Balance length changes by \(22.5 \mathrm{~cm}\)

In second case \(X^{\prime}=\frac{2 \times 3}{2+3}=1.2 \Omega\)
\(\frac{2}{\ell}=\frac{1.2}{100-\ell}\)
\(200-2 \ell=1.2 \ell\)
\(\ell=\frac{200}{3.2}=62 . \mathrm{bm}\)
Balance length changes by \(22.5 \mathrm{~cm}\)

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