JECRC UNIVERSITY
B.Sc.-LLB (SEM-1)
Optics
Assignment-II
Section A
1. Phase Difference between two successive Fresnel’s half period zones is:
a) 0
b) Π/2
c) Π
d) 2π
2. The phenomenon of diffraction was discovered by
a) Fresnel
b) Fraunhofer
c) Huygen
d) Grimaldi
3. The radii of half period zones are proportional to
a) 1/√n
b) 1/n
c) n
d) √n
4. A diffraction pattern is obtained using a beam of red light. What happens if the red
light is replaced by the blue light?
a) No change
b) Diffraction bands become narrower and crowded together
c) Bands become broader and farther apart
d) Bands disappear
5. We cannot get diffraction from a wide slit illuminated by a monochromatic light.
a) True
b) False
6. Diffraction of sound waves is more evident in daily life than light waves
a) True
b) False
7. If the Fresnel’s distance is a, then what should be the distance of the screen from the
slit, d, such that ray optics is no longer valid?
a) d > a
b) d < a
c) d = a
d) No relation between d and a
8. Which of the following diagrams represents the diffraction patterns of two points that
are just resolved?
a)
b)
c)
d)
A
B
C
D
9. The diagram below shows, rays from two wavelet that will meet at first minimum.
The path difference will be?
a)
b)
c)
d)
λ/2
λ
bλ
b/λ
10. Interference fringes may or may not be of the same width while diffraction fringes are
not of the same width.
a) True
b) False
Section B
1) Why the diffraction of sound is more evident in daily life than light waves?
2) Radio waves diffract pronouncedly around buildings while light waves which are also
electromagnetic waves do not, why?
3) Distinguish between interference and diffraction?
4) Light of 5000 Å is incident on a circular hole of radius 1 cm. How many half period
zones are contained in the circle if the screen is placed at a distance of 1 m?
Section C
1) What are Fresnel’s half period zones? Why they are called half period zones?
2) In a Michelson interferometer experiment, when 100 fringes were shifted the final
reading of the screw was found to be 10.735 mm. of wavelength of light is 5.92x10-5
cm then what was the initial reading of the screw?
Section D
1) Write short notes ona) Fresnel’s assumptions
b) Coherence length
c) Wave train
d) Spectral purity
e) Visibility as a measure of coherence
2) In Michelson interferometer experiment sodium light is used which has lightof
wavelength 5890 Å and 5896 Å. Calculate the necessary displacement of mirror for
producing two consecutive positions of maximum distinctions of interference
patterns.