(a) Properties of photon which describe the particle nature of electromagnetic radiation:
(i) Photons are quanta or discrete packet of energy.
(ii) Energy of photon is proportional to the frequency of the em radiation.
(iii) Photon transfers its whole energy to the interacting electron.
(b) Einstein's photoelectric equation:
KEmax‌=hv−hv0
(i) KE‌=eVS
If negative potential of magnitude V s is applied to the anode then no photoelectron electron will be able to reach anode and hence the photoelectron emission will stop. This potential is known as stopping potential.
(ii) From Einstein's equation, When
v=v0,KEmax=0, i.e., photoelectrons are just emitted with no kinetic energy.
When v>v0,KEmax>0, i.e., photoelectrons are emitted with some kinetic energy.
When v<v0,KEmax<0, which is not possible. So, no photoelectron emission takes place.
So, there is a minimum frequency below which photoelectron emission is not possible. This frequency is known as threshold frequency.