Question

j. j. thomson observed that a cathode ray is diverted by electrically-charged metal plates. the ray was attracted by a positive plate and repelled by a negative plate. what conclusion did thomson draw from his observations?
there are negatively charged particles in the atom.
there are neutrons in the atom.
he did not find anything important from his work.
he discovered the nucleus of the atom.

Explanation:

• Recall the principles of electric charge interaction: opposite charges attract, like charges repel.
• Thomson's observation: cathode ray was attracted to positive plate (so ray has negative charge) and repelled by negative plate (consistent with negative charge).
• Analyze options:
• "There are negatively charged particles in the atom": Consistent with cathode ray (electrons) being negatively charged, so this is correct.
• "There are neutrons in the atom": Neutrons were discovered later (by Chadwick), not by Thomson's cathode ray experiment.
• "He did not find anything important...": His work was crucial (discovered electrons), so this is wrong.
• "He discovered the nucleus...": Rutherford discovered the nucleus, not Thomson.

Answer:

A. There are negatively charged particles in the atom.