A source of constant potential difference is connected across a conductor having irregular cross section as shown.

Options

A. Electric field intensity at P is greater than that at Q
B. Rate of electrons crossing per unit area of cross-section at P is less than that at Q
C. The rate of generation of heat per unit length at P is greater than at Q.
D. Mean kinetic energy of free electrons at P is greater than that at Q.

Answer

B

Explanation

When a source is connected, a current starts to flow through the conductor. Let it be I. Then current density at a section is equal to I//A where A = cross-sectional area. Since cross-sectional area at P is maximum, therefore current density at P is minimum. Hence (2) is correct.
Since electric field is `(J)’/(sigma)(=(I)/(Asigma)=(Isigma)/(A))`,therefore at P electric field is minimum while that at Q is maximum.
Rate of generation of heat per unit length at a section will be equal to`(I^(2)p)/(A)`.It is minimum at Q.