 # Physical Optics MCQs

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

Answer: Option C

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

Answer: Option D

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

Answer: Option C

24. 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

Answer: Option C

25. 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

Answer: Option B

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

Answer: Option C

27. 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

Answer: Option B

28. 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

Answer: Option D

29. 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

Answer: Option C

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

Answer: Option A

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