Question

Cathode rays have:
A. mass only
B. charge only
C. both mass and charge
D. neither mass nor charge

Answer 1

The properties of a cathode ray can be explained by a discharge tube experiment. Cathode rays are made of electrons. Whether they have mass can be explained by the fact that these rays can rotate a spinning wheel kept in their path. And whether they have charge is explained by the fact that they get attracted to the anode electrode.

Complete step by step answer:
The first attempt made to discover cathode rays was done by J.J. Thompson. Let us see what he did in his experiment:
The experimental setup consisted of an evacuated glass tube fitted with a cathode at one end and an anode at the other, connected to a high voltage power supply. Let us see what he observed on passing current through the tube:
On passing current, he observed that a faint green glow starting from the anode flowed the length of the tube, till it reached the anode. He concluded that since the rays are getting attracted towards a positively charged plate (anode), the rays must consist of negatively charged particles. Thus, he proved that cathode rays have charge.
His next experiment tells us about their mass:
He placed a spinning wheel in the path of the rays and observed that the wheel started to rotate. This indicated that the particles of the ray imparted some mechanical energy to the wheel, and thus, the particles must possess some mass.
Hence, from his experiment, we can conclude that cathode rays have both charge and mass.

So, the correct answer is Option C .

Note: J.J. Thompson is credited with the discovery of electrons, which he accomplished through his discharge tube experiment. Discharge tubes were later on used for many applications, such as being the main component in cathode ray tube televisions (box TVs). Note that the quantity of the charge possessed by a single electron was later discovered by Millikan, through his oil drop experiment.