Question

If diameter of a conductor is doubled , then drift velocity of electrons inside it will not change

Although we have the relation I = neaVd

Answer 1

Drift velocity is independent of the diameter or cross-sectional area of the conductor. For the same p.d. V across the conductor, increase of cross-sectional area decreases the resistance R = (rho)(length)/(cross-sectional area) and thus increases the current (I = V/R).

but I is proportional to cross-sectional area A, since I = nqvA. Drift velocity remains unchanged.