In the photoelectric effect, if you increase the light intensity while the frequency is above threshold, what happens to the number of emitted electrons and to their maximum kinetic energy?

In the photoelectric effect, if you increase the light intensity while the frequency is above threshold, what happens to the number of emitted electrons and to their maximum kinetic energy?

• A. Number of emitted electrons decreases; maximum KE increases
• B. Number of emitted electrons increases; maximum KE increases
• C. Number of emitted electrons unchanged; maximum KE decreases
• D. Number of emitted electrons increases; maximum KE remains about the same

Answer: (D)

In the photoelectric effect, light delivers energy in packets called photons. If the frequency is above the threshold, each photon has enough energy to overcome the work function and eject an electron. The maximum kinetic energy of the emitted electrons is given by KE_max = h f − phi, which depends on the photon energy (h f) and the work function (phi), not on how many photons arrive. When you raise the light intensity at the same frequency, you increase the number of photons hitting per second. That means more electrons are ejected, so the emission rate goes up. But because the photon energy hasn't changed, the maximum kinetic energy of the emitted electrons remains about the same.

In the photoelectric effect, light delivers energy in packets called photons. If the frequency is above the threshold, each photon has enough energy to overcome the work function and eject an electron. The maximum kinetic energy of the emitted electrons is given by KE_max = h f − phi, which depends on the photon energy (h f) and the work function (phi), not on how many photons arrive.

When you raise the light intensity at the same frequency, you increase the number of photons hitting per second. That means more electrons are ejected, so the emission rate goes up. But because the photon energy hasn't changed, the maximum kinetic energy of the emitted electrons remains about the same.