Are you a fan of science fiction?
In some 1950s science fiction stories, one of the space travel themes was the use of solar sails for propulsion. The idea was that the photon pressure from the sun would push the sail (like wind sails) and move the space craft. What once was science fiction is now reality as solar sails are being developed and tested for modern space travel.
Photoelectric Effect and the Particle Nature of Light
The photoelectric effect is a phenomenon that occurs when light shined onto a metal surface causes the ejection of electrons from that metal. It was observed that only certain frequencies of light are able to cause the ejection of electrons. If the frequency of the incident light is too low (red light, for example), then no electrons were ejected even if the intensity of the light was very high or it was shone onto the surface for a long time. If the frequency of the light was higher (green light, for example), then electrons were able to be ejected from the metal surface even if the intensity of the light was very low or it was shone for only a short time. This minimum frequency needed to cause electron ejection is referred to as the threshold frequency.
Classical physics was unable to explain the photoelectric effect. If classical physics applied to this situation, the electron in the metal could eventually collect enough energy to be ejected from the surface even if the incoming light was of low frequency. Einstein used the particle theory of light to explain the photoelectric effect as shown in Figure below.
- Light has properties of both a wave and a particle.
- The photoelectric effect is produced by light striking a metal and dislodging electrons form the surface of the metal.
- What are the properties of a photon?
- What does the photoelectric effect show about the properties of light?
- How does the frequency of light affect the release of photons?