COMEDK 2025 Afternoon Solved Paper

Concept:Drift velocity in a conductor depends directly on the current, which is inversely proportional to resistance for a fixed voltage.Explanation:The wires are made of the same material and have the same cross‑sectional area.Hence, their resistance is proportional to length: $R \propto L$.Given lengths: $L_A = 10$ cm, $L_B = 40$ cm, so $R_A : R_B = 10 : 40 = 1 : 4$.The wires are connected in parallel to the same $10$ V source, so the voltage across each is equal.From Ohm’s law, $I = V / R$, the currents are inversely proportional to resistance:$I_A : I_B = R_B : R_A = 4 : 1$.Drift velocity is given by $v_d = \frac{I}{n A e}$, where $n$, $A$, and $e$ are the same for both wires (same material and geometry).Thus, $v_d \propto I$, and the ratio of drift velocities equals the ratio of currents:$v_{dA} : v_{dB} = I_A : I_B = 4 : 1$.Answer:$\displaystyle \frac{V_{dA}}{V_{dB}} = 4 : 1$. This corresponds to option C.