Q71 / 90 · JEE Main 2022 (27 Jul Shift 2) · Physics

A. The drift velocity of electrons decreases with the increase in the temperature of conductor.
B. The drift velocity is inversely proportional to the area of cross-section of given conductor.
C. The drift velocity does not depend on the applied potential difference to the conductor.
D. The drift velocity of electron is inversely proportional to the length of the conductor.
E. The drift velocity increases with the increase in the temperature of conductor.

Choose the correct answer from the options given below:

  • A
    A and B only
  • Correct answer
    B
    A and D only
  • C
    B and E only
  • D
    B and C only

Solution

Drift velocity =eτmE

vd=eτmΔVl

ΔV= Potential difference applied across the wire As temperature increases, relaxation time decreases, hence Vd decreases.
As per formula, Vd∝1l

vd=I neA , as it is not mentioned that current is at steady state neither it is mentioned that n is constant for given conductor. So it can't be said that vd is inversely proportional to A.

I=neAvd=VR=VρlA

vd=eEτm

τ decrease with temperature increase.

First and fourth statements are correct.

vd=Vρlne  E=Vl

Hence, the correct answer is option: 'B'.

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