Exam-style question
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Which observation indicates that cathode rays are not simply ionised gas molecules?.
- A.Cathode rays are emitted from the cathode surface.
- B.Cathode rays are deflected by electric fields.
- C.Cathode rays are visible as a faint blue glow.
- D.Cathode rays are unaffected by magnetic fields.
Model answer
What a good answer should say
- Cathode rays are emitted from the cathode surface.
Explanation
Why this works
evidence: Cathode rays originate directly from the cathode, not from the gas between electrodes. interpretation: If they were ionised gas molecules, they would be produced throughout the tube.
implication: Emission solely from the cathode shows the particles are emitted from the metal surface. conclusion: The cathode-origin evidence supports that cathode rays are streams of electrons, not ionised gas.
Common mistake
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