Free Discovery of the Proton MCQs with Answers

1. Positive rays were used in the discovery of the proton. These rays were produced from

• A. the cathode of the discharge tube
• B. the residual gas atoms losing electrons in a discharge tube
• C. the radioactive decay of uranium
• D. the anode metal evaporating

Explanation: Goldstein observed that cathode rays travelling through a perforated cathode knocked electrons off the residual gas atoms, leaving positive ions that streamed towards the cathode as canal rays. Their charge to mass ratio depended on which gas was in the tube, and it was largest for hydrogen, identifying the proton. Cathode rays themselves are electrons and come from the cathode.

2. The proton was discovered through experiments on

• A. cathode rays
• B. positive rays produced in a discharge tube with a perforated cathode
• C. radioactive decay of uranium
• D. the photoelectric effect

Explanation: Goldstein observed rays travelling towards the cathode and passing through holes in it, and the lightest positive particles, obtained when hydrogen filled the tube, were identified as protons. Cathode rays led to the electron instead, which is the pairing this question tests. The charge to mass ratio of these positive rays depended on the gas used, unlike that of cathode rays.

3. Unlike cathode rays, the properties of positive rays depend on the gas in the discharge tube because

• A. positive rays are electromagnetic waves
• B. the positive ions formed are the ionised atoms of that particular gas
• C. positive rays travel faster
• D. the cathode is perforated

Explanation: Positive rays are the residue of atoms that have lost electrons, so their mass differs from gas to gas, whereas cathode rays are electrons and are identical whatever the source. This difference was itself strong evidence that the electron is a universal constituent of all matter. The lightest positive particle, from hydrogen, was named the proton.