The drift velocity of electrons for a conductor connected in an electrical circuit is V_d. The conductor in now replaced by another conductor with same material and same length but double the area of cross section. The applied voltage remains same. The new drift velocity of electrons will be

Solution

Physics sir · 4 steps

Drift speed depends on the field inside the wire, and doubling the area does not change that field.

1. Use the field. Electrons drift because of the electric field in the conductor: v_d = μ E = eEτ/m. The field in a uniform wire is E = V/l.

   v_d = eτ/m·V/l

2. Check what changed. Same material, so τ and n are unchanged. Same V and same l, so E is unchanged. The area A does not appear in v_d at all.
3. Cross-check with current. Doubling A halves the resistance, so the current doubles: I' = 2I. Then v_d = I/neA becomes 2I/ne(2A), the same as before.
4. So. The new drift velocity is V_d, option (b).

The idea to keep. At fixed voltage, drift velocity depends only on V/l and the material. A thicker wire carries more current, but the electrons do not move any faster.

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