Two coherent sources produce interference fringes with an intensity ratio of $81:1$. Find the ratio of the maximum to the minimum intensity in the interference pattern.

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 the phase difference between the two waves is:

Light waves are emitted by a common source. For what time interval will the phase remain constant?

When a light wave enters from air into water, which quantity does not change?

The difference in the number of wavelengths, when yellow light propagates through air and vacuum columns of the same thickness, is $1$. The thickness of the air column is (Refractive index of air $\mu_a = 1.0003$, Wavelength of yellow light in vacuum $\lambda_0 = 6000 \text{ Å}$)

$A$ beam with wavelength $\lambda$ falls on a stack of partially reflecting planes with separation $d$. The angle $\theta$ that the beam should make with the planes so that the beams reflected from successive planes may interfere constructively is (where $n = 1, 2, \dots$)