Wednesday, 17 April 2019

photoelectric effect


Photoelectric effect:-
according to quantum theory of light,



When electromagnetic waves propagate it carries energy in packet or pieces ( it means that energy is quantized )


Electromagnetic energy carries in packet or pieces according to quantum theory of light given by Einstein.


This packet of energy called photon and the energy of photon is given by

  E = hf, 
where h is Planck's constant and f is the frequency.


ACCORDING TO ABOVE RELATION, amount of energy related to frequency of that wave.


If we increase frequency we increase amount of energy (of photon).


What quantum mechanics tell us about subatomic particle?


especially electron.


Electromagnetic waves carry amount of energy In the same way , electron also carry some amount of energy.


As we study in chemistry, normally electron remain in ground state (lowest level of energy) when some amount of energy given to electron and it able to overcome coulomb force of attraction between electron and proton .

then electron gets excited move in excited state but remain there temporary it soon releases energy and return back to its ground state it releases energy in the form of light.


Same phenomenon used by Einstein to give photoelectric effect,

We all know about electrostatics force, proton in nucleus pull electron with a coulomb force,in order to free electron we have to provide more energy than that coulomb force.


Einstein conducted a experiment,


,he took a electron, He said that ,I shine light on my electron and that light have low energy that not high enough to excite a electron 


Then he increase intensity of that light and find that electron was not excited even now, then he said if light travels like a wave (according to it energy of light proportional to it intensity  i.e, more the intense of light ,more energy it carries.)


If there is increase in energy, by increasing intensity my electron must get excited. but that was not happen here.


Now, from quantum theory of light, we know that light carries energy in the form of packet known as quanta energy it carries is given as ,

  E = hf, 
where h is Planck's constant and f is the frequency.

From above equation we know that energy directly proportional to frequency. what happens if we increase frequency of light in above experiment . 
Einstein reconduct the experiment and find that on increasing the frequency electron gets excited .


IT MEANS THAT LIGHT TRAVEL IN THE FORM OF PARTICLE



Photoelectric effect gives experimental prove to quantum theory of light.



 now, question arises what is photoelectric effect?


The photoelectric effect s the emission of electrons from the surface of matter generally, a metal in response to the incident light. 
but in a condition that frequency of incident light must be greater than threshold frequency (it is a minimum frequency require to electron gets excited or gets free ).

Energy contained within the incident light is absorbed by electrons within the metal, giving the electrons sufficient energy to be knocked out or get free of the surface of the metal.

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