Einstein's Photoelectric Equation - Practice Questions & MCQ

Einstein's Photoelectric equation-

As we studied that E = hν  is the equation of energy of each photon. Now we have also studied that the threshold frequency is that frequency below which the electrons won’t come out of the metallic surface. From the above equation we see that Energy is a function of frequency. Now one question will come in mind that when the electron gets ejected then where does all the electron goes?? Does that electron have some energy to go any where??? If yes then which type of energy??

All these type of question was well answered by the greta scientist Albert Einstein, According to the experiment performed by the Albert Einstein, there are some conclusion that those electron have kinetic energy only. Also the energy absorbed by the photons is partly used to overcome the force by the metallic surface. SInce there is no electric field present outside the metallic surface so there will be only energy present is pure kinetic energy. 

So, we have K.E. of the photo-electrons = (Energy obtained from the Photon) – (The energy used to escape the metallic surface)

Here, The energy used to escape the metallic surface is the wrok function $(\phi)$ which we have discussed already. So the Einstein's Photoelectric equation can also be written as -

$$
\text { K.E. }=\mathrm{hv}-\Phi
$$

We can understand the work function more clearly like this -
As we know that an electron needs some minimum energy to be extracted from a metallic surface. So from the above equation, if $\mathrm{v}=$ threshold frequency ( $\mathrm{v}_0$ ) then the electrons gets just enough quantum energy to come out of the metal. It means that the Kinetic Energy of such an electron will be zero. So we can write that -

$$
\mathrm{hv}_0-\Phi=0 \text { or } \mathrm{hv}_0=\Phi
$$
 

This is the relation between the threshold frequency and the work function. We can also change this equation in terms of the threshold wavelength.