Photoelectric Effect Physics

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Photoelectric Effect Physics

Photons

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These are the packets of energy which are emitted by a source of radiation.

They travel in straight line with speed same as that of light with energy            

E = hv.

Physics Photoelectric Effect

It is the phenomenon of emission of electrons from the surface of metals when light radiations of suitable frequency fall on them.

The emitted electrons are called photoelectrons and the current so produced is called photoelectric current.

Applications of Photoelectric Cells

The most important application of photoelectric call is in the reproduction of sound in cinema, television and phototelegraphy (long transmission of pictures in very short time).

The temperature of celestial bodies is measured and their spectra are studied by using these cells.

Automatic Doors

These cells are used in opening and closing of doors automatically.

In Automatic switches for street lights.

Electric Eye

The electric eye is also called the thief-detector bell. It is used for giving theft – warning in banks, treasuries etc.

Complexion Meters

The photoelectric cells may be used to compare dark, whitish and white faces.

The light reflected from the face is allowed to fall on the photoelectric cell and the current produced is measured.

Whiter the face more is the reflected light and more will be the current produced by the cell.

Thus the current is a measure of the face complexion.

Space

Photoelectric cells are also used in obtaining electrical energy from sunlight during space travel.

Memorable Points

  • Electrons of different kinetic energies are emitted from the metal surface even if the light of single frequency is allowed to fall on the metal plates.
  • The reason is that the electrons coming from interior of metal lose some of their energy in colliding with the positive ions.
  • The electrons emitted from the metal surface have maximum kinetic energy.

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