DNE | PHYSICS |U10|T10
Dainey Education and Research
-----------------------------------------------------------------------------------------------------------------------------------------------------------
Physics
Unit Test - X
12th – Standard(CBSC)
Time : 1 Hour
Mark : 70
1.
What is the phenomenon that occurs when light passes through a narrow slit and spreads out?
a) Diffraction b) Refraction
c) Reflection
d) Dispersion
2. What type of interference is observed when two light waves are in phase?
a) Destructive interference
b) Constructive interference
c) No interference
d) Partial interference
3. Which of the following is a characteristic of light waves that shows diffraction?
a) Light has a large wavelength
b) The light source is a monochromatic laser
c) The size of the slit is comparable to the wavelength of light
d) Light has no frequency
4. The angular width of the central maximum in a single-slit diffraction pattern depends on which of the following?
a) Wavelength of light and slit width
b) Wavelength of light and screen distance
c) Slit width and screen distance
d) Only wavelength of light
5. In the Young's double-slit experiment, the distance between the slits is 2 mm and the distance between the screen and the
slits is 1.5 m. If the wavelength of light used is 600 nm, what is the fringe separation?
a) 0.5 mm
b) 0.6 mm
c) 1.2 mm
d) 1.8 mm
6. In Young’s double-slit experiment, the path difference between two waves at a point on the screen is 2λ. What type of
interference will be observed at this point?
a) Constructive interference
b) Destructive interference
c) No interference
d) Total reflection
7. The angular separation between the central maximum and the first-order minimum in a single-slit diffraction is 30°. What is
the wavelength of light used if the slit width is 1 mm?
a) 300 nm
b) 600 nm
c) 900 nm
d) 1200 nm
8. Which of the following phenomena cannot be explained by the particle theory of light?
a) Reflection
b) Refraction
c) Diffraction
d) Photoelectric effect
9. The number of maxima (including the central maximum) observed in a single-slit diffraction pattern is 5. What is the total
number of minima observed?
a) 4
b) 5
c) 6
d) 7
10. What is the main condition for the occurrence of diffraction?
a) The wavelength of light must be much smaller than the size of the aperture
b) The size of the aperture must be smaller than the wavelength of light
c) The aperture must be of any size
d) Diffraction does not occur with light waves
Answer: b) The size of the aperture must be smaller than the wavelength of light
11. In a diffraction pattern due to a single slit, what is the distance between the first minimum and the central maximum?
a) λ/2
b) λ
c) 2λ
d) λ/4
12. In Young’s double-slit experiment, if the slit separation is doubled, what happens to the fringe width?
a) It becomes half
b) It becomes double
c) It remains the same
d) It becomes four times
13. In diffraction at a single slit, the angle θ of the first minimum is related to the wavelength λ and the slit width 'a' by the
equation:
a) a sin(θ) = λ
b) a sin(θ) = 2λ
c) a sin(θ) = 3λ
d) a sin(θ) = 4λ
14. What is the order of the central maximum in a Young’s double-slit experiment?
a) First-order maximum
b) Zero-order maximum
c) Second-order maximum
d) Third-order maximum
15. In the phenomenon of diffraction, if the wavelength of light increases, what happens to the diffraction pattern?
a) It becomes narrower
b) It becomes wider
c) It remains unchanged
d) It disappears
Answer All the questions (5*2=10)
16. State the reason, why two independent sources of light cannot be considered as coherent sources.
17. Define the term ‘coherent sources’ which are required to produce interference pattern in Young’s double slit experiment.
18. Define the term ‘wavefront’
19. Why does Sun appear red at sunrise and sunset?
20. Define the term ‘linearly polarised light’. When does the intensity of transmitted light become maximum, when a polaroid
sheet is rotated between two crossed polaroids?
1
DNE | PHYSICS |U10|T10
Dainey Education and Research
----------------------------------------------------------------------------------------------------------------------------------------------------------Answer All the questions (5*3=15)
21. (i) State the principle on which the working of an optical fiber is based.
(ii) What are the necessary conditions for this phenomenon to occur?
22. Yellow light (λ = 6000Å) illuminates a single slit of width 1 x 10-4 m. Calculate
(i) the distance between the two dark lines on either side of the central maximum, when the diffraction pattern is viewed on
a screen kept 1.5 m away from the slit;
(ii) the angular spread of the first diffraction minimum.
23. A parallel beam of light of 500 nm falls on a narrow slit and the resulting diffraction pattern is observed on a screen 1 m
away. It is observed that the first minimum is at a distance of 2.5 mm from the centre of the screen. Calculate the width of
the slit.
24. (a) Write the conditions under which light sources can be said to be coherent.
(b) Why is it necessary to have coherent sources in order to produce an interference pattern?
25. Write the distinguishing features between a diffraction pattern due to a single slit and the interference fringes produced in
Young’s double slit experiment?
Answer All the questions (6*5=30)
26. Draw the intensity pattern for single slit diffraction and double slit interference. Hence, state two differences between
interference and diffraction patterns.
27. How is a wavefront defined? Using Huygen’s construction draw a figure showing the propagation of a plane wave refracting
at a plane surface separating two media. Hence verify Snell’s law of refraction.
28. (a) Describe briefly, with the help of suitable diagram, how the transverse nature of light can be demonstrated by the
phenomenon of polarization.
(b) When unpolarized light passes from air to a transparent medium, under what condition does the reflected light get
polarized?
29. How is a wavefront defined? Using Huygen’s construction draw a figure showing the propagation of a plane wave reflecting
at the interface of the two media. Shpw that the angle of incidence is equal to the angle of reflection.
30. (a) How does an unpolarized light incident on a polaroid get polarized?
Describe briefly, with the help of a necessary diagram, the polarization of light by reflection from a transparent medium.
(b) Two polaroids ‘A’ and ‘B’ are kept in crossed position. How should a third polaroid ‘C’ be placed between them so that
the intensity of polarized light transmitted by polaroid B reduces to 1/8* of the intensity of unpolarized ‘ light incident on A?
31. (a) A point object ‘O’ is kept in a medium of refractive index n1 in front of a convex spherical surface of radius of curvature R
which separates the second medium of refractive index n2 from the first one, as show in the figure.
Draw the ray diagram showing the image formation and deduce the relationship between the object distance and the image
distance in terms of n1, n2 and R.
(b) When the image formed above acts as a virtual object for a concave spherical surface separating the medium n2 from
n2 (n2 > n1), draw this ray diagram and write the similar [similar to (a)] relation. Hence obtain the expression for the lens
maker’s formula
2