(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 :

Solution

Physics sir · 2 steps

Write drift velocity in terms of V, L and τ, then test every statement against it.

1. Build the formula. An electron in field E accelerates for an average time τ between collisions, so v_d = eEτ/m. Across a wire of length L the field is E = V/L.

   v_d = eVτ/mL

   Statement	What the formula says	Verdict
   (A) decreases as temperature rises	Hotter lattice means more frequent collisions, so τ falls and v_d falls	True
   (B) v_d ∝ 1/A	Area A does not appear, so v_d does not depend on A	False
   (C) independent of V	v_d ∝ V	False
   (D) v_d ∝ 1/L	L sits in the denominator, so v_d ∝ 1/L	True
   (E) increases as temperature rises	Opposite of (A), because τ gets shorter	False

2. So. Only (A) and (D) are correct, which is option (b).

The idea to keep. For drift velocity, start from v_d = eVτ/mL. It shows what matters (V, L, τ) and what does not (area). Heating the wire shortens τ, so the drift gets slower.

Answer from the NTA final answer key. Solution by PrepWiser.