Newton’s rings are formed with reflected light of wavelength 589 nm using a plano- convex lens and a plane glass plate with a liquid between them. The diameter of the

15^th ring is 5.1 mm and radius of curvature of the curved surface of the lens is 1 m.

Calculate the refractive index of the liquid if the ring is dark.

Explain the propagation of light through optical fibre. What are the advantages of

using optical fibres for communication?

A single slit has a width of 0.04 mm. A parallel beam of light of wavelength 560 nm is incident normally on it. If the distance between the slit and the screen is 100 cm, calculate the separation between the central maximum and the second minima in the diffraction pattern.

A thin film of glass of refractive index 1.5 is inserted in one arm of Michelson Interferometer. Calculate the thickness of the film if a shift of 10 fringes is observed. The wavelength of the light used is 589 nm.

What is a zone plate? How does a positive zone plate differ from a negative zone plate? Show that each Fresnel half period zone has nearly the same area

Unpolarised light is incident on two polarizing sheets placed over one another. The intensity of light transmitted finally is one-third of the intensity of the incident light. Calculate the angle between the transmission axes of the two polarizing sheets.

A light of amplitude ‘a’ is incident obliquely on a parallel thin film. If ‘r’ and ‘t’ represent the fractions of incident light reflected and transmitted respectively, draw a diagram to explain multiple reflection of incident light and write the amplitudes of successive rays.