Question

Albert Einstein, the great physicist proposed a clear picture to explain photoelectric effect.
a) Explain Einstein's photo electric equation.
b) Name the quanta of light.

Answer 1

a) Einstein realised that it actually takes energy for an electron to leave the surface of the metal. He called this energy the work function, $\varphi$.

He applied the Conservation of Energy Principle for an electron receiving energy and leaving the metal. Compare energy received and used by the electron at the surface.

Energy supplied to the electron, $E=hf$ (energy from the photon)

Energy used by the electron is either: used as work function to escape from the surface or is left with the electron after it has escaped, in which case it is in the form of kinetic energy, $E_k$

So for each electron at the surface which leaves the metal:

Energy supplied = energy used

$hf=\varphi +E_k$

This is Einstein's Photoelectric Equation.

b) According to Plank's quantum theory, light is emitted from a source in the forms of bundles of energy called photons - quanta of light.