Exam-style question
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Which experimental finding best explains why cathode rays can be focused into a narrow beam?.
- A.Cathode rays are neutral and can be collimated by lenses.
- B.Cathode rays are charged and can be steered by electric fields.
- C.Cathode rays are magnetic and can be guided by magnets.
- D.Cathode rays are photons and can be focused by mirrors.
Model answer
What a good answer should say
- Cathode rays are charged and can be steered by electric fields.
Explanation
Why this works
evidence: Cathode rays can be focused into a beam using electric plates that deflect them. interpretation: Only charged particles can be steered by electric fields.
implication: The ability to focus the rays confirms their charged nature. conclusion: The focusing by electric fields demonstrates that cathode rays are charged particles.
Common mistake
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