Question

Which of the following is the formula for calculating coherence time?

(a) Τc = \(\frac {\lambda^3}{(c\Delta \lambda)}\)

(b) Τc = \(\frac {\lambda}{(c\Delta \lambda)}\)

(c) Τc = \(\frac {\lambda^2}{(c\Delta \lambda)}\)

(d) Τc = \(\frac {\lambda^2}{(c\Delta \lambda)}\)

This question was addressed to me in an internship interview.

Enquiry is from Coherent and Incoherent Addition of Waves topic in portion Wave Optics of Physics – Class 12

Answer 1

Right answer is (d) Τc = \(\frac {\lambda^2}{(c\Delta \lambda)}\)

Easiest explanation: The formula for calculating coherence time is given as:

Τc = \(\frac {\lambda^2}{(c\Delta \lambda)}\)

Where Τc is the coherence time, λ is the wavelength, ∆λ is the spectral width of the source, and c is the speed of light in a vacuum (i.e. 3 × 10^8 m/s).