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Section B (Paragraph/Problem Type)

Answer all questions in a paragraph of about half a page to one page.
Each correct answer carries a maximum of 5 marks.

What do you mean by athin lens? Write down the thin lens formula and explain the terms involved.

Interference fringes are observed with a biprism of refracting angle 1° and refractive index 1.5 on
a screen 0.8 m from it. If the distance between the source and the biprism is 0.2 m, estimate the
fringe width when a light of wavelength 690 nm is used.

Obtain the radii of the first two dark rings of the Fraunhofer diffraction pattern produced by a
circular aperture of radius 0.02 cm at the focal plane of a convex lens of focal length 20 cm. Given,

the wavelength 2 = 600 nm.

Consider a diffraction grating having 15000 lines per inch. Obtain the angular separation of the
D, and D, lines of sodium in the second order spectra.

Determine the radius of the first zone in a zone plate of focal length 20 cm for light of wavelength
500 nm.

Using a suitable figure, explain the reconstruction of image in holography.

A step index fiber has a core of refractive index 1.55 and cladding of refractive index 1.5. Determine
the numerical aperture of the fiber. Assume that light enters the fiber from air.

(Ceiling - 30 marks)
Section C (Essay Type)

Answer in about two pages, any one question.
Correct answer carries 10 marks.

Using a suitable figure, discuss the principle, construction and working of a Michelson
interferometer. Discuss the condition for obtaining brightness in circular rings.

Using suitable figures, explain the optical activity of substances. Discuss the Fresnel’s explanation

of optical rotation.

(1 x 10 = 10 marks)

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