981. The appearance of colour in thin films is due to
A. Diffraction
B. Dispersion
C. Interference
D. Polarization

982. The blue colour of the sky is due to
A. Diffraction
B. Reflection
C. Polarization
D. Scattering

983. A light ray travelling from rarer to denser medium suffers a phase change of
A. 60°
B. 90°
C. 180°
D. 45°

984. When one mirror of a Michelson Interferometer has moved a distance of 0.5 mm we observe 2000 fringes. What will be the wavelength of light used?
A. 5000 nm
B. 5000Å
C. 500m
D. 2000um

985. Diffraction effect is
A. More for round edge
B. Less for round edge
C. More for a sharp edge
D. Less for a sharp edge

986. The wavelengthe of X-rays is of the order of
A. 10 micron
B. 1 angstrom
C. 1 cm
D. 1 m

987. The wavelength of X-rays falling at a glancing angle of 30° on a crystal with atmic spacing 2 x 10-10 for the fist order diffraction is
A. 4 x 10-10 m
B. 2 x 10-10 m
C. 0.02×10-10m
D. 20×10-10m

988. A diffraction grating has 500 lines per mm. Its slit spacing or grating element will be equal to
A. 500 mm
B. 5 x 10-3 mm
C. 2 x 10-5 mm
D. 2 x 10-3 mm

989. In a plane polarized light
A. Vibration in all direction
B. Vibration in two mutually perpendicular directions
C. Vibration take place in a direction perpendicular to the direction of propagation of light
D. No vibration at all

990. Light on passing through a Polaroid is
A. Plane polarized
B. Un-polarized
C. Circularly polarized
D. Elliptically polarized

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