Which scientist demonstrated that cathode rays are streams of negatively charged particles?

Which scientist demonstrated that cathode rays are streams of negatively charged particles?

• A. Joseph John Thomson
• B. Rutherford
• C. Marie Curie
• D. Albert Einstein

Answer: (A)

The concept being tested is identifying who showed that cathode rays are actually streams of negatively charged particles, i.e., the existence of the electron through cathode-ray experiments. J. J. Thomson carried out classic experiments with a vacuum tube where the cathode ray could be deflected by electric and magnetic fields. By analyzing how the beam bent, he determined a charge-to-mass ratio characteristic of a particle much lighter than atoms and clearly bearing negative charge. This demonstrated that cathode rays are not just a gas glow or a property of the tube, but consist of negatively charged subatomic particles—electrons. Thorough measurements and the consistency of the results across different setups solidified the conclusion and reshaped the understanding of atomic structure. Rutherford’s work, for example, looked at how atoms are structured and led to the idea of a nucleus, not the charge nature of cathode rays. Curie’s discoveries focused on radioactivity, not the charge of cathode-ray particles. Einstein contributed foundational ideas in quantum theory and the photoelectric effect, not the demonstration that cathode rays are negatively charged particles. So Thomson’s experiments uniquely establish the negative-charge electron as the component of cathode rays.

The concept being tested is identifying who showed that cathode rays are actually streams of negatively charged particles, i.e., the existence of the electron through cathode-ray experiments. J. J. Thomson carried out classic experiments with a vacuum tube where the cathode ray could be deflected by electric and magnetic fields. By analyzing how the beam bent, he determined a charge-to-mass ratio characteristic of a particle much lighter than atoms and clearly bearing negative charge. This demonstrated that cathode rays are not just a gas glow or a property of the tube, but consist of negatively charged subatomic particles—electrons. Thorough measurements and the consistency of the results across different setups solidified the conclusion and reshaped the understanding of atomic structure.

Rutherford’s work, for example, looked at how atoms are structured and led to the idea of a nucleus, not the charge nature of cathode rays. Curie’s discoveries focused on radioactivity, not the charge of cathode-ray particles. Einstein contributed foundational ideas in quantum theory and the photoelectric effect, not the demonstration that cathode rays are negatively charged particles. So Thomson’s experiments uniquely establish the negative-charge electron as the component of cathode rays.