Exam-style question
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Which of the following best explains why light is emitted immediately when a metal surface is struck by light of a frequency above the threshold frequency?.
- A.Because the light transfers enough energy to the electrons to overcome the work function.
- B.Because the light increases the temperature of the metal, causing electrons to escape.
- C.Because the light creates a magnetic field that pushes electrons out of the metal.
- D.Because the light changes the chemical composition of the metal surface.
Model answer
What a good answer should say
- Because the light transfers enough energy to the electrons to overcome the work function.
Explanation
Why this works
The photon theory states that each photon carries energy E=hf. If hf exceeds the metal’s work function, an electron can absorb the photon’s energy and be emitted immediately.
This accounts for the threshold frequency and the lack of delay, matching the objective.
Common mistake
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