Question

J.J. Thomson's cathode-ray tube experiment demonstrated that

• A. cathode rays are streams of negatively charged ions
• B. all the mass of an atom is essentially in the nucleus
• C. the \(\frac em\) of electrons is much greater than the \(\frac em\) of protons
• D. the \(\frac em\) ratio of the cathode ray particles changes when a different gas is placed in the discharge tube

Answer 1

The Correct Option is C

J.J. Thomson's cathode-ray tube experiment was a pivotal experiment in the study of atomic structure, specifically regarding the properties of electrons. Let's examine the key points:

1. Objective of the Experiment: J.J. Thomson aimed to investigate the nature of cathode rays. He used a cathode ray tube, a sealed glass tube from which most of the air had been evacuated. When a high voltage was applied, it produced a glowing beam.
2. Discovery: Thomson discovered that cathode rays were deflected by both magnetic and electric fields. This deflection indicated that cathode rays consisted of charged particles.
3. Charge and Mass Determination: Through a series of measurements, Thomson was able to determine the charge-to-mass ratio (\frac{e}{m}) of the particles in the cathode rays. He found that these particles, later identified as electrons, had a much smaller mass compared to known atoms and molecules.
4. Finding: The key finding of Thomson's experiment was that the \(\frac{e}{m}\) of electrons is much greater than the \(\frac{e}{m}\) of protons. This result implies that electrons are much lighter than protons.

Based on these steps and findings, the correct answer is: "the \(\frac em\) of electrons is much greater than the \(\frac em\) of protons". This conclusion is consistent with the substantially smaller mass of the electron compared to the proton.