Question

a beam of cathode ray is subjected to crossed electric and magnetic field. The field are adjusted such that the beam is not deflected. The specific charge of cathode rays is given by

Answer 1

hi friend
here's your answer looking for

in order to understand and answer your question let's first recall the cathode ray tube experiment.

Cathode ray tube experiment :- it was the experiment by which we came to know the most important sub atomic particle of the atom that is electron.
this experiment was performed by JJ Thomson.

so you might be wondering why this tube named as cathode ray tube.
answer is , as this is the ordinary tube that is evacuated and where, there is one anode and one cathode connecting to the high voltage battery.

when all the air inside it, is evacuated by the vacuum pump, then the high voltage is passed through it. and this results as a greenish light ray that is coming from the cathode to anode.

the ray was coming from the cathode that's why it was named as cathode ray.

after this activity performed by the JJ Thomson, he try to perform more activities or experiment on that cathode ray tube, as he was curious enough.

now, he put the electrical and magnetic field around it.
and he was surprised to know that, the cathode ray start showing deflection towards the positive plate .

so, this confirm that the cathode ray has a negative charge in it that make it bend towards the opposite charge that is positive.

that's why the cathode ray is considered to be the negative charge.

in other words it is a stream of a negatively charged particle that is electron.

so, the specific charge of cathode ray is negative

note:- you might be wondering now why that you was evacuated?
answer:- the tube is evacuated because the air is a bad conductor of electricity.
that's why in order to remove that bad conductor the whole tube is evacuated.
so that electricity can travel.

hope you are satisfied with my answer