Question

Which of the following is correct about the specific charge of cathode ray particles?
${\text{A}}{\text{.}}$ Depends on nature of the cathode
${\text{B}}{\text{.}}$ Depends on the nature of anode
${\text{C}}{\text{.}}$ Depends on nature of gas atoms present inside discharge tube
${\text{D}}{\text{.}}$ Independent of all the above

Answer 1

Hint: Here, we will proceed by discussing important features of the cathode rays and how exactly electrons were discovered. We will also write down some of the observations made by Thomson during his experiment.

Complete step-by-step answer:

Cathode rays are streams of electrons found in vacuum tubes (also called an electron beam or an e-beam). When an evacuated glass tube is equipped with two electrodes and a voltage is applied, it is found that the glass opposite the negative electrode glows from the electrons emitted from the cathode. The first observations of electrons as constituents of cathode rays were. The picture in a classic television set is generated by a concentrated beam of electrons in cathode ray tubes (CRTs) deflected by electric or magnetic fields.

Thomson was able to calculate the mass to charge ratio of the particles by measuring the extent of deflection of the cathode rays in magnetic or electric fields of different strengths. These particles were released by the negatively charged cathode, and repelled by an electric field's negative terminal. Since, like charges repel each other whereas unlike (or opposite charges) attract each other, Thomson concluded that the particles had a net negative charge and these particles are known as electrons.

Thomson observed that the mass to charge ratio of cathode rays is always independent of the nature of the metal electrodes or the gas, indicating that electrons are fundamental components of all atoms.

So, from the above discussion it is clear that the specific charge of cathode ray particle is negative (which is a universal constant because these particles are electrons only) and therefore, these are independent of the nature of the cathode or the nature of anode or the nature of the gas atoms present inside the discharge tube.

Hence, option D is correct.

Note: Cathode rays are called this way as they are generated in a vacuum tube by the negative electrode, or cathode. They must first be detached from cathode atoms to release electrons into the tube. The early cold cathode vacuum tubes, called Crookes tubes, had a high electrical potential for ionizing the residual gas in the tube between the anode and cathode.