Question

An electron moves along a metal tube with variable section. The velocity of the electron when it approaches the neck of tube, is

Answer 1

An electron moves along a metal tube with variable section as shown in figure.

The velocity of the electron $\textbf{increases}$, when it approaches the neck of tube.

as you know, when a charge is placed near the conducting material, an induced charge is produced on that material.

here, same concept is used. an electron moves within metal tube , due to negative charge on electron a opposite nature charge induced on the neck. due to opposite nature, an electrostatic force of attraction acts between them. this force accelerates the electron. That's why velocity of electron increases when it approaches the neck of the tube.