A graph is plotted between current density (on x-axis) and drift velocity (on y-axis). The slope of the graph is
(n is the number density of free electrons and e is the charge of an electron)
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 1/(ne)
Current density is the current per unit area, and the current is carried by electrons moving with the drift velocity:
\( \displaystyle j = \frac{I}{A} = ne\,v_d \)
\( \displaystyle v_d = \frac{1}{ne}\,j \)
So a graph of \( v_d \) (y-axis) against j (x-axis) is a straight line through the origin with slope 1/(ne).