Chapter 27, Problem 1CQ

To determine

The description of the photoelectric effect and how the photon model of light explained the experimental results of the effect.

Answer to Problem 1CQ

Photoelectric effect is the phenomenon in which the electrons are ejected from metals when light of certain frequency is incident on them. Photon model of light explained the experimental results of the effect using the quantum nature of light.

Explanation of Solution

Photoelectric effect is the phenomenon in which the electrons are ejected from the surface of a metal when electromagnetic radiation of appropriate frequency is incident on it. The first puzzling feature of the photoelectric effect was that the brighter light increases the current of electrons, but does not affect their kinetic energy. Photon model explains this as with the increasing intensity, more photons collide with the material thus more electrons are ejected. However, this does not increase the kinetic energy of an individual electrons since atoms are so small that two photons are hardly ever absorbed by the same atom.

The second characteristic that could not be explained by classical theory was that maximum kinetic energy of the electrons depends on the wavelength of the incident radiation. This can be explained as shorter wavelength radiation has higher energy and this will provide more kinetic energy to the ejected electrons. The third characteristic is that photoelectric effect will not occur below a threshold frequency of the incident radiation. This can be understood as certain minimum amount of energy is required to free the electrons from the material to which they are bound. The final characteristic that puzzled the nineteenth century scientists was that the electrons are emitted virtually instantaneously after turning on a photon source. This is explained as each individual electron carries enough energy to cause the photoelectron to be emitted. Since only a single photon is required to eject an electron, the process happens instantaneously.

Conclusion:

Thus, the photoelectric effect is the phenomenon in which the electrons are ejected from metals when light of certain frequency is incident on them. Photon model of light explained the experimental results of the effect using the quantum nature of light.