Exam-style question
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Which observation from early cathode ray experiments most directly indicates that cathode rays are made of charged particles?.
- A.Cathode rays are deflected by a magnetic field.
- B.Cathode rays produce a fluorescent glow on the glass tube.
- C.Cathode rays can be seen as a faint blue light.
- D.Cathode rays are emitted from the cathode at a constant speed.
Model answer
What a good answer should say
- Cathode rays are deflected by a magnetic field.
Explanation
Why this works
evidence: In experiments, cathode rays were observed to bend when a magnetic field was applied perpendicular to their path. interpretation: The bending shows that the rays respond to magnetic forces, which only act on moving charges.
implication: Therefore the rays must consist of charged particles moving through the tube. conclusion: The deflection by a magnetic field is the key evidence that cathode rays are streams of charged particles.
Common mistake
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