Practice question · Multiple choice
The photoelectric effect shows that dim blue light ejects electrons while intense red light does not. Why could no wave theory explain this?
Hints
- On a wave picture, what should turning up the brightness of red light eventually achieve?
- Ask what it means that the threshold depends on colour rather than on brightness.
Show the answer
D. Because a wave's energy depends on intensity, not on frequency
Why
A wave should let intensity substitute for frequency, pour in enough red light and an electron accumulates the energy. It never happens, which means energy arrives in quanta of size hf: one photon, one electron, and a red photon simply is not big enough. This is the paper that won Einstein the Nobel Prize.
Practise Mathematical Methods in Physics
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