Question

A current passes through a wire of nonuniform cross-section. Which of the following quantities are independent of the cross-section?

• A. The charge crossing in a given time interval
• B. Drift velocity
• C. Current density
• D. Free-electron density

Answer 1

Answer: (A), (D)

The correct options are
A The charge crossing in a given time interval
D Free-electron density

As the current passes, the value of current at any point in the circuit remains the same. Therefore the charge crossing in any given interval is same and does not change with the cross section of the wire
$I=JA$
As $A$-cross section of wire changes, $J$-current density changes and $I$ current remains same.
The free electron density is a property of the material and doesnot change when current passes.
As the cross section changes, current density changes and hence the drift velocity changes.