Photoelectric Effect

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Photoelectric Effect

• (How Einstein really became famous!)

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Photoelectric Effect
Metal Foil
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Photoelectric Effect
Metal Foil
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Photoelectric Effect

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

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Photoelectric Effect
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Photoelectric Effect

• When red light hits the metal foil, the foil does
  not emit electrons.
• Blue light has more energy than red light.
• How could we get more energy into the red light?
• Try increasing the brightness.

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Photoelectric Effect
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Photoelectric Effect

• Well, that didnt work!
• Maybe its still not bright enough.

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Photoelectric Effect
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Photoelectric Effect

• Still not working.
• What happens with brighter blue light?

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Photoelectric Effect
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Photoelectric Effect

• More blue light means more electrons emitted, but
  that doesnt work with red.

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Photoelectric Effect
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Photoelectric Effect

• Wave theory cannot explain these phenomena, as
  the energy depends on the intensity (brightness)
• According to wave theory bright red light should
  work!

• BUT IT DOESNT!

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Photoelectric Effect

• Einstein said that light travels in tiny packets
  called quanta.
• The energy of each quanta is given by its
  frequency

frequency
Ehf
Energy
Plancks constant
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Photoelectric Effect

• Each metal has a minimum energy needed for an
  electron to be emitted.
• This is known as the work function, W.
• So, for an electron to be emitted, the energy of
  the photon, hf, must be greater than the work
  function, W.
• The excess energy is the kinetic energy, E of the
  emitted electron.

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Photoelectric Effect
EINSTEINS PHOTOELECTRIC EQUATION-
E hf-W
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Photoelectric Effect

• For a further demonstration try this website-The
  Photoelectric Effect

Try to find the work functions of
- Aluminium Silver Copper Sodium Platinum
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By Maruthupandi M , M.sc chemistry
,vivekanada college,Madurai.