Two light waves having the same wavelength in vacuum are in phase initially

PHYSICS · Single correct · CBSE · Physics · Wave Optics · Wave Optics

Problem

Two light waves having the same wavelength

\lambda

in vacuum are in phase initially. Then the first wave travels a path

L_1

through a medium of refractive index

n_1

while the second wave travels a path of length

L_2

through a medium of refractive index

n_2

. After this, what is the phase difference between the two waves? (1)

\frac{2\pi}{\lambda} \left( \frac{L_2}{n_1} - \frac{L_1}{n_2} \right)

(2)

\frac{2\pi}{\lambda} \left( \frac{L_1}{n_1} - \frac{L_2}{n_2} \right)

(3)

\frac{2\pi}{\lambda} (n_1 L_1 - n_2 L_2)

(4)

\frac{2\pi}{\lambda} (n_2 L_1 - n_1 L_2)