A current-carrying ohmic metal wire has a cross-sectional area that gradually be
ID: 1424004 • Letter: A
Question
A current-carrying ohmic metal wire has a cross-sectional area that gradually becomes smaller from one end of the wire to the other. The current has the same value for each section of the wire, so charge does not accumulate at any one point.
(a) How does the drift speed vary along the wire as the area becomes smaller?
(a) it increases
(b) it decreases
(c) it remains constant
(b) How does the resistance per unit length vary along the wire as the area becomes smaller?
(a) it increases
(b) it decreases
(c) it remains constant
Explanation / Answer
The drift speed increases.
it's similar to the equation of continuity for fluids A1V1=A2V2. So as the cross sectional area gets smaller, the velocity must increase to keep the equation true.
As the cross-sectional area A decreases, the drift velocity must increase in order for the constant current to be maintained, As current decreases, therefore R increases.