compton effect

Compton Effect:

        Photoelectric effect proved quantum theory of light at basic level.

·         It confirmed that light consist of individual photon that carry energy, depends upon frequency of oscillation of light.

·         Another experiment that proved quantum theory of light was Compton effect

·         In Compton effect, Compton makes electromagnetic waves with shorter wavelength (x rays) to fall at stationary electron,

·         he examined collision between the electromagnetic waves and electron,

·         he found that reflected electromagnetic wave has greater wavelength than the wave incident on electron on collision.

·         “Wavelength of the scattered X rays was larger than incident X rays in collision of X rays and a stationary electron, this effect is known as Compton effect”

·         Using conservation of energy and momentum, he was able to derive the following equation,

·         Compton shift =shift in wavelength

·         This is known as Compton shift

·         Now question arises how Compton Effect proves quantum theory of light?

·         According to wave theory there is no change take place in wavelength in any collision.

·         The incident electromagnetic wave cause electron to oscillate with same frequency as that of incident waves when the electron reemitted the waves its must be of same frequency as that of incident waves so there is no shift in frequency which implies there is no shift in wavelength according to wave theory

·         But this is not happen in actual experiment conducted by Compton, in Compton experiment there is a shift in Wavelength.

·         It proves that wave theory is not applicable here, from quantum theory of light ,lets examined Compton experiment through quantum theory of light and found that  it is applicable or not

·         Lets photon collides with that stationary electron and in this collision some of energy within photon goes into the electron, (similarly the case of particles collision in which transfer of energy take place).

·         Now, electron gain kinetic energy and begin to move with same velocity and scattered photon has less energy than before.

·         Energy depends on frequency, less energy means less frequency and smaller frequency means greater wavelength as frequency is inversely proportional to wavelength.

·         So that scattered waves has larger wavelength and therefore quantum theory of light is successfully describe Compton experiment related to Compton effect  and its contrary is also true.

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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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