Question

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 electron beam has a uniform cross-section.
Which of the following statement(s) is/are correct?

• A. The speed of the electron is more at $B$ than at $A$.
• B. The electric current is from left to right.
• C. The magnitude of the current is larger at $A$ than at $B$.
• D. The current density is more at $B$ than at $A$.

Answer 1

Answer: (A)

The speed of the electron is more at $B$ than at $A$.

The direction of electric field is from right to left. Hence the potential at $B$ is higher than potential $(E_x=\frac{dV}{dx})$ at point A, so the speed of electron is more at $B$ than at $A$.