Which fundamental particle did J.J. Thomson discover through his cathode ray experiments?

• A. Electron
• B. Nucleus
• C. Neutron
• D. Proton

Answer: (A)

Verified step by step guidance

1. Understand the context of J.J. Thomson's cathode ray experiments, which involved studying the properties of cathode rays in vacuum tubes.
2. Recall that cathode rays were found to be streams of negatively charged particles, which were much smaller than atoms.
3. Recognize that J.J. Thomson concluded these particles were fundamental components of atoms, leading to the discovery of a new particle.
4. Identify that this newly discovered particle is the electron, characterized by its negative charge and very small mass compared to atoms.
5. Note that the nucleus, neutron, and proton were discovered later by other scientists using different experimental methods.