The photoelectric effect provides evidence for the quantum behavior of light because:

photoelectrons are not emitted if the light's frequency is below a certain threshold value
the highest kinetic energy of photoelectrons is determined solely by the light's frequency, not its brightness
photoelectrons are ejected instantly even when the light is very dim
the charge carried by photoelectrons is discrete and quantized

Correct answer: photoelectrons are not emitted if the light's frequency is below a certain threshold value

Solution

The photoelectric effect demonstrates that light behaves as discrete packets of energy (photons). Electrons are only emitted if the light's frequency exceeds a threshold, proving that energy transfer is quantized.

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