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.
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).
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