Question

What change is noticed in cathode ray tubes when the anode voltage is increased?
A. Brightness of the screen increases
B. kinetic energy of electrons reaching the screen increases
C. kinetic energy of electrons reaching the screen decreases
D. kinetic energy of electrons reaching the screen remains the same

Answer 1

Hint- To solve this question, we need to know the basic theory related to the Electromagnetic Deflection in a Cathode Ray Tube. In a cathode ray tube, electrons are accelerated from one end of the tube to the other using an electric field as discussed below.

Formula used- K=eV

Complete step by step solution: -
Kinetic energy of the electrons reaching the screen when voltage v is applied is K=eV
where V is the anode voltage and
e is the electronic charge.

An electron beam is a group of free electrons, all traveling in approximately in the same direction with approximately the same velocity. While it is very difficult to follow where a single electron goes, it is verify easy to follow where a beam of millions (or billions) or electrons go together.

The electron beam is modulated and deflected in a manner which allows an image to appear on the projector. Sometimes, this picture may reflect electrical waveforms (oscilloscope), photographs (television, computer monitor) and so on.

And also, the beam of a single electron can be processed to show movable images in natural colours.

As the anode voltage is applied, the electrons get accelerated at a very high rate which results in increase in the kinetic energy (or velocity) of the electrons.

Therefore, we concluded that kinetic energy of electrons reaching the screen increases.

Thus, option (B) is a correct answer.

Note- Cathode ray experiment was a result of English physicists named J. J. Thomson experimenting with cathode ray tubes. During his various experiments he discovered electrons, which is one of the most important discoveries in the history of physics.