In photoelectric experiments, if light intensity is increased while the photon energy is above threshold, what happens to the rate of electron emission?

In photoelectric experiments, if light intensity is increased while the photon energy is above threshold, what happens to the rate of electron emission?

• A. No electrons are emitted
• B. The emission rate increases with intensity
• C. Each emitted electron gains more kinetic energy
• D. Emission stops

Answer: (B)

The key idea is that the emission rate in the photoelectric effect is tied to how many photons are arriving, assuming each photon has enough energy to overcome the work function. When the photon energy is above threshold, electrons can be emitted, and increasing the light’s intensity simply increases the number of photons hitting the surface per second. Since each emitted electron requires a photon, more photons mean more electrons are emitted per unit time. The kinetic energy of each emitted electron, however, is set by the excess energy of the photon over the work function (hf − φ) and does not depend on how many photons arrive. So, raising intensity boosts the emission rate but leaves the electrons’ kinetic energy per emission unchanged.

The key idea is that the emission rate in the photoelectric effect is tied to how many photons are arriving, assuming each photon has enough energy to overcome the work function. When the photon energy is above threshold, electrons can be emitted, and increasing the light’s intensity simply increases the number of photons hitting the surface per second. Since each emitted electron requires a photon, more photons mean more electrons are emitted per unit time. The kinetic energy of each emitted electron, however, is set by the excess energy of the photon over the work function (hf − φ) and does not depend on how many photons arrive. So, raising intensity boosts the emission rate but leaves the electrons’ kinetic energy per emission unchanged.