If the intensity of incident light is increased (with frequency above threshold), what happens in the photoelectric effect?

• A. The kinetic energy of emitted electrons increases.
• B. More photons are absorbed by the material but the emitted electrons are unchanged.
• C. The kinetic energy of emitted electrons remains the same, but more electrons are emitted.
• D. No electrons are emitted.

Answer: (C)

The main idea is that in the photoelectric effect, each emitted electron’s kinetic energy is set by the energy a single photon provides beyond the work function: KE = hf − φ. If the frequency is above threshold, hf is already greater than φ, so emission occurs and each emitted electron has that same KE for a given frequency. Increasing the light’s intensity raises the number of photons arriving per second, so more electrons can be ejected, but the energy of each emitted electron stays the same because hf (and thus KE) doesn’t change. So the description that matches this is that the kinetic energy remains the same while more electrons are emitted.