Question

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

Answer 1

Hint: First we have to find what is actually the energy required by the electron to escape a metal surface, then we have to find if any excess energy is left inside the electron then what is done with it and in which form it is used. Now we have to form an equation using the law of conservation of energy. Now as energy can never be destroyed, so it will stay in the electron (if any excess energy is there). For the second part of the question we have to understand the concept of light bundles.

Formula Used:
$E=hf$
$hf=\varphi +E_k$

Complete step-by-step answer:
a)
We know that sir Albert Einstein actually realized that, for an electron to leave the surface of metal it actually requires a fixed amount of energy and this energy is called a work function and it is represented by the symbol $\varphi$ (phi).
Now, Einstein applied the principle of conservation of energy Principle on an electron that is consuming energy and leaving the metal surface. Then we need to compare the energy received and used by the electron to exit from that surface.
So, he got the equation by using the formula, $E=hf$ this is actually the energy given from the photon.
Now, this is the total energy that is acquired by the electron, and this energy is used by the electron to escape from the metal surface and if any excess energy is left inside the electron then, it is turned into kinetic energy and used by that electron only.
So, we can say that for each electron which leaves the surface of the metal,
Energy Supplied = Energy Used.
We can represent this mathematically by,
$hf=\varphi +E_k$ .
This is also known as Einstein's Photoelectric equation.

b) Now, according to the Planck’s quantum theory, light is actually emitted from a source and this light is formed in forms of bundles of energy which are called quanta and hence it is called quanta of light.

Note: In the equation $hf=\varphi +E_k$, here $\varphi$ is the work function , $E_k$ is the kinetic energy that stays inside the electron, and ‘h’ is the planck's constant and f is the frequency of the electron.