PHOTOELECTRIC EFFECT

                    PHOTOELECTRIC EFFECT 

ELECTRON EMISSION

IT IS THE PHENOMENON IN WHICH LECTRON FROM THE OUTERMOST ORBIT EJECTS OUT WHEN ENERGY IS INCIDENT ON IT WHICH MUST E EQUAL AND GREATER THAN WORK FUNCTION.

WORK FUNCTION

MINIMUM ENERGY IS REQUIRE TO EJECT AN ELECTRON FROM ITS OUTERMOST ELECTRON. BASICALLY, IT IS AN FORM OF IONISATION ENERGY. [IE]

THRESHOLD FREQUENCY

THE MINIMUM FREQUENCY WHICH IS REQUIRED TO EJECT AN OUTERMOST ELECTRON BASICALLY IS GIVEN BY THE WORK FUNCTION FROM THE LENS FUNCTION.

TYPE OF ELECTRIC EMISSION

1. THERMIONIC EMISSION:- BY SUITABLY HEATING, SUFFICIENT THERMAL ENERGY CAN BE IMPARTED TO THE FREE ELECTRONS TO ENABLE THEM TO COME OUT OF THE METAL.

2. FIELD EMISSION:- BY APPLYING A VERY STRONG ELECTRIC FIELD. ELECTRONS CAN BE PULLED OUT OF THE METAL, AS IN A SPARK PLUG.

3. PHOTO-ELECTRIC EMISSION:- WHEN LIGHT OF SUITABLE FREQUENCY ILLUMINATES A METAL SURFACE, ELECTRONS ARE EMITTED FROM THE METAL SURFACE. THESE PHOTOS (LIGHT)-GENERATED ELECTRONS ARE CALLED PHOTOELECTRONS.

PHOTOELECTRIC EFFECT

PHOTOELECTRIC EFFECT IS A PHENOMENON IN WHICH WHENEVER LIGHT OF SUITABLE FREQUENCY IS MADE TO INCIDENT ON LIGHT-SENSITIVE METALS PLATES ITS ELECTRON WILL EJECT OUT AND DUE TO THE MOTION OF THESE PHOTOELECTRONS TOWARDS THE ANODE, YOU WILL OBTAIN PHOTOCURRENT IN THE SUBSTANCE. IN THIS WAY THE LIGHT ENERGY IS CONVERTED INTO ELECTRIC ENERGY.

LAWS OF PHOTOELECTRIC EFFECT

THERE ARE 4 LAWS OF PHOTOELECTRIC EFFECT:-

LAW-1

 PHOTOSENSITIVE MATERIAL AND FREQUENCY OF INCIDENT RADIATION [ABOVE THE THRESHOLD FREQUENCY], THE PHOTOELECTRIC CURRENT IS DIRECTLY PROPORTIONAL TO THE INTENSITY OF INCIDENT LIGHT.

LAW 2

FOR A SOME PHOTOSENSITIVE MATERIAL AND FREQUENCY OF INCIDENT RADIATION, SATURATION CURRENT IS FOUND TO BE PROPORTIONAL TO THE INTENSITY OF INCIDENT RADIATION WHEREAS THE STOPPING POTENTIAL IS INDEPENDENT OF ITS INTENSITY.

LAW 3 

FOR A GIVEN PHOTOSENSITIVE MATERIAL, THERE EXISTS A CERTAIN MINIMUM CUT-OFF FREQUENCY OF THE INCIDENT RADIATION CALLED THE THRESHOLD FREQUENCY, BELOW WHICH NO EMISSION OF PHOTOELECTRONS TAKE PLACE NO MATTER HOW INTENSE THE INCIDENT LIGHT IS ABOVE THE THRESHOLD NO MATTER, THE STOPPING POTENTIAL OR EQUIVALENTLY THE MINIMUM KINETIC ENERGY OF THE EMITTED PHOTOELECTRONS INCREASES LINEARITY WITH THE FREQUENCY OF THE INCIDENT RADIATION BUT IS INDEPENDENT OF ITS INTENSITY.

LAW 4

THE PHOTOELECTRIC EMISSION IS AN INSTANTANEOUS PROCESS WITHOUT ANY APPARENT TIME LAG, EVEN THE INCIDENT RADIATION IS MADE EXCEEDINGLY DIM.

PHOTOELECTRIC EFFECT AND WAVE THEORY OF LIGHT

THE PHENOMENA LIKE INTERFACE, DIFFRACTION AND POLARISATION WERE EXPLAINED IN A NATURAL AND SATISFACTORY WAY IN THE WAVE PICTURE OF LIGHT.

THE WAVE THEORY OF LIGHT WAS UNABLE TO EXPLAIN THE PHOTOELECTRIC EMISSION AS A MATTER OF FACT:-

THE ENERGY OF THE WAVE IS CONTINUOUS IN SINUSOIDAL FORM BUT FOR THE EJECTION OF ELECTRONS FROM A METAL SURFACE WE NEED A DISCRETE FORM OF ENERGY IN THE FORM OF QUANTA WHICH WERE FURTHER KNOWN AS PHOTONS.

PHOTOELECTRIC EFFECT PROOF THE PARTICLE NATURE OF LIGHT.