The photoelectric effect is the observation that under certain conditions, light striking a metal surface can cause electrons to be ejected. The animation shows red light of low frequency striking a metal surface, but no electrons are emitted from the metal. Even when the light intensity increased, there is still no current flowing. Next, the frequency of light is increased. At a certain particular frequency, current begins to flow. The intensity of light is proportional to the magnitude of the current, but even when the light is very dim current still flows. If light of a higher frequency but the same intensity is used, the current flow is constant. On the other hand, the electrons reach the detector and complete the circuit have more energy than electrons ejected with a lower frequency of light

Questions

1. It takes a certain, minimum amount of energy to free electrons from the metal surface. How does the photon theory of light explain that very intense red light is not able to eject photons? (Hint: photons of light from the red end of the spectrum have less energy than photons of light from the blue end of the spectrum.)

2. Each metal has a very specific light frequency where the photoelectric effect first occurs. What does this minimum frequency represent at the atomic level? (Hint: why don’t electrons just spontaneously leave from the metal surface?)
3. How does the photon theory of light explain the observation that even dim light will cause electrons to be ejected if the frequency of light is at or exceeds the minimum value?
4. Why doesn’t light of a greater frequency, and therefore greater photon energy, cause more photons to be ejected compared to light of the same intensity but lower frequency?