Question

Cathode rays are moving between the poles of a magnet. Due to the effect of magnetic field of magnet:

• A. velocity of rays increase
• B. velocity of rays decrease
• C. rays deflected towards south pole
• D. rays deflected in upward direction and perpendicular to the plane of the paper

Answer 1

The correct option is A velocity of rays increase

A cathods rays are a stream of electrons, when they are passed through magnets, due to magnetic field (of magnets) and velocuity of electrons, Lrents force $(q\overrightarrow{v}\times \overrightarrow{B})$ acts upon them (in the figure its directions is into the page). As the force acts in a direction perpendicular to the initial direction of velocity, the velocity in the directions of force also increases so the net velocity $(|{\overrightarrow{V}}_{net}{|}^2=\sqrt{|{\overrightarrow{V}}_{in}{|}^2+|{\overrightarrow{V}}_{force}{|}^2})$

also increases,

Option $A$ is correct.