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The Photoelectric Effect

The Photoelectric Effect. (or…how Einstein really became famous). Photo (light) + electric. A photoelectric effect is any effect in which light energy is converted to electricity. First explained by Albert Einstein in 1905. When light strikes certain light-sensitive materials….

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The Photoelectric Effect

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  1. The Photoelectric Effect (or…how Einstein really became famous)

  2. Photo (light) + electric • A photoelectric effect is any effect in which light energy is converted to electricity. • First explained by Albert Einstein in 1905

  3. When light strikes certain light-sensitive materials… • It may cause them to give up electrons.

  4. Photoelectric Effect Metal Foil

  5. Photoelectric Effect Metal Foil

  6. Photoelectric Effect • As blue light strikes the metal foil, the foil emits electrons.

  7. Photoelectric Effect

  8. Photoelectric Effect • When red light hits the metal foil, the foil does not emit (give off) electrons. • Blue light has more energy than red light. • How could we get more energy into the red light? • Try increasing the brightness (intensity).

  9. Photoelectric Effect

  10. Photoelectric Effect • That didn’t work • Maybe its still not bright (intense) enough.

  11. Photoelectric Effect

  12. Photoelectric Effect • Still not working. • What happens with brighter (more intense) blue light?

  13. Photoelectric Effect

  14. Photoelectric Effect • More blue light means more electrons emitted, but that doesn’t work with red.

  15. Photoelectric Effect

  16. Photoelectric Effect • High FREQUENCY light even from a dim source can eject electrons from a photosensitive metal • Low Frequency light, even very bright (very intense) cannot dislodge electrons

  17. Photoelectric Effect • Light, like all other radiation, is made up of small particles called photons. • The higher the frequency, the more energy the photons have. • Einstein stated that light interacts with matter as a stream of particle-like photons. • Einstein received the Nobel Prize for this discovery.

  18. Einstein won the Nobel Prize for the Photoelectric Effect, not E= mc²

  19. Photoelectric Effect • If a photon hits an atom of a certain material, it may be absorbed by an electron of that material. • However, if the photon has enough energy, the electron is ejected, or emitted, from the atom. • In this way, light energy changes into electrical energy.

  20. Photoelectric Effect • If wires are attached to a photoemittive material, the electrons can flow along the wires, forming an electric current.

  21. WHY IS THE PHOTOELECTRIC EFFECT SO IMPORTANT? • It helped explain the particle nature of light. • It is the basis of the quantum theory. • It is used in photocells e.g. in solar calculators, alarms, automatic garage door openers, flash of a camera

  22. Burglar Alarms • When the light source to the semiconductor is interrupted by a person walking through the beam of light, a switch is activated that triggers the alarm.

  23. Review- Photoelectric Effect • What it is : The ejection of electrons from certain metals when light falls upon them. The metals are said to be photosensitive (sensitive to light) • Who and When: Einstein explained the photoelectric effect in 1905, but won the Nobel Prize in 1921

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