Question

A potential difference v exists between the ends of a metal wire of length l. The drift velocity will be doubled if

• A. v is doubled
• B. l is doubled
• C. The diameter of the wire is doubled
• D. The temperature of the wire is doubled

Answer 1

The correct option is A v is doubled

The drift velocity is $v_d=\frac{eVt}{2ml}$
The relaxation time t changes with change of temperature. Actually it decreases with rise of temperature. Thus at a given temperature drift velocity is directly proportional to the potential difference, inversely proportional to length and is independent of cross-sectional area.
So when drift velocity is doubled , V becomes double and l is half.