(i) When the applied potential difference V is halved, the electric field across the conductor will also be halved. We know, drift velocity vd is directly proportional to the electric field. Therefore, vd will also be halved.
(ii) When L is doubled, the resistance (R=ρL/A) will also double. Hence, current (I=V/R) will be halved. We know that the current is directly proportional to vd. Therefore, vd will also be halved.
(iii)When D is doubled, there is no change in the electric field across the conductor. Hence, no change in the drift velocity vd.
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