23.2. Photons and the Photoelectric Effect http://www.ck12.org
23.2 Photons and the Photoelectric Effect
Objectives
The student will:
- Understand photons.
- Understand the mechanism photoelectric effect.
- Solve problems involving the photoelectric effect.
Vocabulary
- photoelectric cell:A sealed glass chamber with a vacuum inside, and a gap between the wide metal plate on
the negative side and the small metal plate on the positive side. The light source is set up to shine light on the
wide metal surface. - photoelectric effect:Describes how light gives energy to electrons, allowing them to jump across an electric
field. - photon:Particle of light.
- work function:The minimum energy(Eo)E 0 =h f 0 needed to overcome the electrical forces which bind the
electron within the metal.
Introduction
Thephotoelectric effectdescribes how light gives energy to electrons, allowing them to jump across an electric
field. The basic experimental setup is shown below. Thephotoelectric cellis a sealed glass chamber with a
vacuum inside, and a gap between the wide metal plate on the negative side and the small metal plate on the positive
side. The light source is set up to shine light on the wide metal surface.
The ammeter on the circuit shows current results when light shines on the wide metal surface. It is understood that
the light gives energy to the electrons, enabling some of them to jump across the vacuum gap to the other side.
TheFigure23.6 shows the result when the light is turned on. It was clear that light somehow initiated a current, by
causing electrons from the metal surface to jump across the gap to the anode. The electrons crossing are shown as
blue dashed lines.
There are two fundamental parameters that can be varied in the effect:
- The frequency of the light
- The intensity of the light