How does Einstein’s theory of the photoelectric effect challenge the classical wave theory of light?

In the photoelectric effect, the intensity of light affects only the number of electrons emitted, not whether they are emitted or their energy:

1. Number of electrons: Higher intensity light has more photons hitting the material per second, so more electrons are ejected if the light frequency is above the threshold.
2. Energy of electrons: The intensity does not affect the energy of the emitted electrons. Each electron’s energy depends only on the frequency of the light, not on how bright it is.
3. No emission below threshold: Even extremely intense light cannot emit electrons if its frequency is below the material’s threshold frequency.

Key point:

• Frequency determines if electrons are emitted and how energetic they are.
• Intensity determines how many electrons are emitted, provided the frequency is high enough.