Uses and effects of the

Photoelectric Effect

Space Shuttles Because of the photoelectric effect the sun's

rays can cause the panels of a spaceship to collect a static charge.

Conversely, shadowed parts of the craft can become negative from the expelled electrons interacting with plasma. The result of this could cause a discharge through the vehicle frying onboard electronics.

Film

1)Film is made up of photocells.

2)Track modulates the intensity of the light at a frequency which is the same as the sound which was used to produced the track.

Night Vision Devices

The energy causing the screen of a night vision device to light up is triggered by photons hitting a plate of gallium arsenide.

Light: Waves or Particles?

One important use of the Photoelectric is helping to prove light is made up of tiny particles called photons, as opposed to waves. The results of the photoelectric effect come out differently depending on whether light consists of particles or waves.

If light is made up of particles:

the energy given off by those waves would depend solely on the light's intensity, or Amplitude. Other factors, like the frequency, should make no difference. As an example, two different lights of the same intensity should knock out the same number of electrons, and the maximum kinetic energy of both sets of electrons should also be the same. Decrease the intensity, and you should get fewer electrons, flying out more slowly; if the light is too faint, you shouldn't get any electrons at all, no matter what frequency you're using.

Simple, Right? C:\Users\Andrew\Pictures\waves.gif

This is not the case.

Although the previous was the accepted truth for a long bloody time, an actual experiment predicts the true verdict.

The TRUTH

Higher-frequency photons have more energy, so they should make the electrons come flying out faster; thus, switching to light with the same intensity but a higher frequency should increase the maximum kinetic energy of the emitted electrons. If you leave the frequency the same but crank up the intensity, more electrons should come out (because there are more photons to hit them), but they won't come out any faster, because each individual photon still has the same energy.

Truth (cont.)

If the frequency is low enough, then none of the photons will have enough energy to knock an electron out of an atom. So if you use really low-frequency light, you shouldn't get any electrons, no matter how high the intensity is. Whereas if you use a high frequency, you should still knock out some electrons even if the intensity is very low.

In Conclusion

Therefore, with a few simple measurements, the photoelectric effect would seem to be able to tell us whether light is in fact made up of particles or waves. (hint: they have mass)

Questions

1.What small particles are removed from a metal as the result of the photoelectric effect?

2.Is the amount of energy released dependent on frequency or amplitude?

3.Does the photoelectric effect support the theory of light as waves or particles?