Question

The diagram shows part of an evacuated tube in which a stream of electron from an electron gun passes between a pair of parallel large deflecting plates. The vertical displacement of the electron beam as it leaves the parallel plates is $x$. (Do not consider gravity and the electron enters the deflecting region parallel to the plates). Which one of A to D below will change the displacement $x$ of the beam as it leaves the parallel plate?

• A. Increasing the accelerating voltage.
• B. Increasing the deflecting voltage.
• C. Increasing the distance between the electron gun and the deflecting plates.
• D. Increasing the distance between the two deflecting plates.

Answer 1

Answer: (A), (B), (D)

Increasing the accelerating voltage.
Increasing the deflecting voltage.
Increasing the distance between the two deflecting plates.

When increases the accelerating voltage, speed of electron also increase. Therefore it will decreasing the time spent between the plates and it will reduce x.
Increasing deflecting voltage means increasing the electric field between the plates, making acceleration of electron greater.
Increasing the distance between the electron gun and the deflecting plates means no effect on x because speed of electron remains same as there no gravity.
Increasing the distance between the two deflecting plates means reducing x.
therefore, $\left(A\right),\left(B\right),\left(D\right)$ are the correct option.