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JEE Mains · Physics · STD 12 - Current electricity
  • JEE Mains 2024
  • Hard
  • Numerical

Two wires \(A\) and \(B\) are made up of the same material and have the same mass. Wire A has radius of \(2.0 \mathrm{~mm}\) and wire \(B\) has radius of \(4.0 \mathrm{~mm}\). The resistance of wire B is \(2 \Omega\). The resistance of wire \(\mathrm{A}\) is _______ \(\Omega\).

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Answer & Solution

Correct Answer

(D) \(32\)

Step-by-step Solution

Detailed explanation

\(\because \mathrm{R}=\frac{\rho \ell}{A}=\frac{\rho \mathrm{V}}{\mathrm{A}^2}\)

\(\therefore \frac{\mathrm{R}_{\mathrm{A}}}{\mathrm{R}_{\mathrm{B}}}=\frac{\mathrm{A}_{\mathrm{B}}^2}{\mathrm{~A}_{\mathrm{A}}^2}=\frac{\mathrm{r}_{\mathrm{B}}^4}{\mathrm{r}_{\mathrm{A}}^4}\)

\(\Rightarrow \frac{\mathrm{R}_{\mathrm{A}}}{2}=\left[\frac{4 \times 10^{-3}}{2 \times 10^{-3}}\right]^4\)

\(\Rightarrow \mathrm{R}_{\mathrm{A}}=32 \Omega .\)

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