Electrons are emitted by a hot filament and are accelerated by an electric field as shown in figure. The two stops at the left ensure that the electrons beam has a uniform cross-section.

Question

Philoid · Accepted Answer

Electric field is in the direction form right to left.

Let velocity of an electron at stop A is

velocity of an electron at stop A is

Potentials are increased in the opposite direction of electric field.

So

Potential energy of the electron at point A is

Potential energy of the electron at point B is

Because

Kinetic energy of an electron at point A is

Kinetic energy of an electron at point B is

Applying conservation of mechanical energy , we get

(Mechanical energy =potential energy+kinetic energy)

(Because

Speed of electron is more at stop B than stop A. Option A is correct.