Optics Answers

helium - neon laser emits a diffraction
limited beam (X = 600 nm) of diameter
3 x 10 - 3m. Calculate the diameter of the
light patch produced on the surface of moon
at a distance of 376 >: 103 km from the Earth.
Assume that scattering in Earth's
atmosphere can be ignored.

If the
angle subtended at the hologram by the
signal and the reference beam is 15°, what
is the wave length of light used which
produces fringes separated by a distance
1.8micrometer?

Using the stellar interferometer, Michelson
observed for the star Betelgeuse that the
fringes disappear when the distance
between movable mirrors is 65 cm.
Assuming l. = 6 x 10 ^(—5)cm, calculate the
angular diameter of the star.

Calculate the
thickness of a quarter wave plate for light of wave
length 5000 A . The refractive indices for o-ray and
e - ray are 1.553 and 1.544 respectively.

Calculate the radius of the first and third
zones in a zone plate of focal length 20 cm
for light of wavelength 5000A.

The energy radiated by the sun is
approximately 4 x 1026Js -1. If the sun is
assumed to be sphere of radius 7 x 108m,
calculate the Pyointing vector at its surface.

The coherence length for sodium D2-line is
2.5 cm. Calculate the coherence time t and
the spectral width of the line. Take
X=6 x 10^(-5) cm.

A step index fibre 6.35 x 10-5 m in diameter
has a core of refractive index 1.52 and a
cladding of refractive index 1.47. Determine
the numerical aperture for the fibre and the
acceptance angle.

Obtain the
expression for area of the nth zone.

Newton's rings are formed in reflected light
of wavelength 6000A with a liquid between
the plane and curved surfaces. The diameter
of 7thdark ring is 0.34 cm and the radius of
curvature of curved surface is 100 cm.
Calculate the refractive index of liquid.