Question

Which law is used for achieving the relation between the Einstein’s coefficients?

(a) Heisenberg’s Uncertainty Principle

(b) Planck’s radiation law

(c) Einstein’s equation

(d) Quantum law

I got this question in an interview.

This key question is from Einstein Coefficients topic in section Laser of Engineering Physics II

Answer 1

Correct option is (b) Planck’s radiation law

To explain I would say: Planck’s radiation law, which gives the energy density u = \(\frac{8πhv^3}{c^3} \frac{1}{e^α-1}\), is used as the formula resembles the one for the energy density of the external radiation field in stimulated emission, u = \(\frac{A_{21}}{B_{21}(\frac{B_{12}}{B_{21}}e^α-1)}\).