Question

A source of constant potential difference is connected across a conductor having irregular cross-section as shown in the figure –

• 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 that at Q
• D. Mean kinetic energy of free electrons at P is greater than that at Q

Answer 1

Answer: (B)

Rate of electrons crossing per unit area of cross-section at P is less than that at Q

Answer 2

Cross section at P is maximum at P

\ current density at P is minimum

Q E = rJ

\Electric field at P is also minimum. E_P < E_Q,

i_P = i_Q

Ž J_P < J_Q , V_P < V_Q

Heat per unit length = $\frac{i^{2}Rt}{\mathcal{l}}$= $\frac{\mathcal{l}^{2}\rho t}{A} \propto \frac{1}{A}$Q R = $\frac{\rho\mathcal{l}}{A}$