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JEE Mains · Physics · STD 12 - Current electricity
  • JEE Mains 2021
  • Hard
  • MCQ

In the given figure, a battery of emf \(E\) is connnected across a conductor \(P Q\) of length \('Y'\) and different area of cross-sections having radii \(r_{1}\) and \(r_{2}\left(r_{2}\,<\,r_{1}\right)\). Choose the correct option as one moves from \(P\) to \(Q\) :

Pick an option to check your answer.
Verified Solution

Answer & Solution

Correct Answer

(B) Drift velocity of electron increases.

Step-by-step Solution

Detailed explanation

Current is constant in conductor

\(i=\) constant

Resistance of element \(d R=\frac{\rho d x}{\pi r^{2}}\)

\(d V=i d R=\frac{i \rho d x}{\pi r^{2}}\)

\(E=\frac{d V}{d x}=\frac{i \rho}{\pi r^{2}}\)

\(V_{d}=\frac{e E \tau}{m}\)

\(\therefore V_{d} \propto E\)

\(\rightarrow E \propto \frac{1}{r^{2}}\)

if \(r\) decreases, \(E\) will increase \(: V_{d}\) will increase

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