Two identical conducting wires, A and B of different materials, are joined in series across a battery. If the number density of electrons in A is thrice that in B, then the ratio of drift velocity of electrons in the two wires is

1 : 3

The correct answer is Option (3) → 1 : 3

Current in series: I = n e A v_d ⇒ v_d = \frac{I}{n e A}

Given: $n_A = 3n_B$

$v_A = \frac{I}{n_A e A} = \frac{I}{3n_B e A} = \frac{1}{3} v_B$

∴ Ratio $v_A : v_B = 1 : 3$