The photoelectric effect occurs when light striking a surface, usually a metal surface, results in the emission of electrons from the surface. The emitted electrons are called photoelectrons. The photoelectric effect can be explained if light is considered to consist of a stream of photons. The intensity of the light relates to the number of photons in the stream, and the energy of the light is related to the frequency of the photons. The energy of a photon striking the surface is absorbed by an electron within the metal. If the energy of the photon is high enough, the electron will be ejected from the surface of the metal, if the energy of the photon is not high enough, the electron will stay where it is. Since a more intense light source has more photons, it will eject more electrons from a surface than a less intense source will. The kinetic energy of the photoelectron depends on the energy of the incident photon, not the number (the intensity) of incident photons.

The following simulation allows you to control the intensity and wavelength of a light source that is aimed at a piece of metallic sodium. As you change the characteristics of the photons, you will be able to observe the photoelectric effect.

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Source: Photoelectric Effect, University of Colorado – Physics

When the simulation opens:

Are any photons emitted from the lamp?

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No

Are there any electrons emitted from the sodium metal surface?

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No

What is the current?

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0 A

Find the two beam control slide bars (Intensity and UV-IR).

Slowly slide the Intensity control to 100% and observe any changes in the simulation.

What happens to the light from the lamp?

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It becomes more intense.

What happens to the sodium?

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It begins to emit electrons.

What happens as the intensity increases?

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More electrons are emitted.

What happens to the current?

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It increases to about 0.141 A.

Keeping the intensity at 100%, adjust the wavelength slider to the right until the wavelength becomes 520 nm.

What happens to the light from the lamp?

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It changes color.

What happens to the number of electrons?

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It stays about the same.

What happens to the speed of the electrons?

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They slow down.

Continue sliding the wavelength slider to the right until the sodium stops producing electrons What is the wavelength?

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540 nm

Now move the wavelength slider all the way to the left
What happens to the electrons?

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They are moving very fast.

What does this show about the photoelectric effect?

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Higher energy photons produce higher energy (faster) electrons; more intense light produces more electrons.