A current-carrying ohmic metal wire has a cross-sectional area that gradually be
ID: 1421947 • 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?
it increases
it decreases
it remains constant
(b) How does the resistance per unit length vary along the wire as the area becomes smaller?
it increases
it decreases
it remains constant
Explanation / Answer
1.The current will remain the same throughout, but the voltage gradient will vary.
2.R=(PL)/A,
Resistance=Resistivity*Cellconstant,
1.When the length of the wire is doubled,its volume remains constant,
therefore,
as,volume=area*length,
=>area=volume/length,
A=V/L,
The resistance is proportional to the length. If the cross section is not changed, then the resistance will be double the initial value.
The resistance is inversely proportional to the cross sectional area.
Resistance = k / (pi r^2)
Here k is a constant. The diameter is doubled, then the radius is doubled. This gives
Resistance = k/(4 pi r^2)