Chapter

24 Wave Optics
TYPE A: MULTIPLE CHOICE QUESTIONS
6 Alight ofintensityl, passes through a material
of thickness d, then the intensity will be
1. Two waves ofintensities I and 41 superimposes. (a) I-,e d. (b) I-I,e (2000)
Then the maximum and minimum intensities are: (c) I=hl -ed (d) none of these
(a) 9I and I (b) 3I and I |1997| 7 Light of wavelength 589.3 nm is incident
(c) 9l and 31 (d) 6l and I normally on a slit ofwidth 0.01 mm. The angular
2. On a rainy day, ifthere is an oil drop on tar road, width of the central diffraction maximum at a
coloured rings are seen around this drop. This distance of I mfrom the slit, is: [2000|
is because of: |1997] (a) 068° (b) 0.34o
(a) total internal reflection of light (c) 2.05° (d) none of these
(b) polarisation 8. In an electron microscope the accelerating
(c) difraction pattern voltage is increased from 20 kV to 80 kV, the
(d) interference pattern produced due to thin resolving power ofthe microscope will become
films
R
3 Interference occurs in which of the following (a) 2R (b) [2000/
2
waves? (1999)
(a) Transverse (b) Electromagnetic (c) 4R (d) 3R
(c) Longitudinal (d) All of these 9. How does the red shift confirm that the universe
4 In young's experiment the monochromatic light is expanding ? (2001/
is used to illuminate two slits A and B as shown (a) wavelength of light emitted by galaxies
appears to decrease
in figure. Interference fringes are observed on a
screen placed in front of the slits. Now a thin (b) wavelength of light emitted by galaxies
glass plate is placed normally in the path ofbeam appears to be the same
coming from the slitA, then: |1999, 2004| (c) wavelength of light emitted by galaxies
appears increase
(d) none of these
10 What change occurs, ifthe monochromatic light
used in Young's double slit experiment is
replaced by white light ? (2001/
(a) onlythe central fringe is white and all other
B fringes are observed coloured.
(b) no fringes are observed.
(a) There will be no change in fringe width (c) all the bright fringes become white.
(b) Fringe width will decrease (d) all the bright fringes are coloured between
violet and red.
(c) Fringe width will increase
(d) Fringes will disappear 11. Light of wavelength 6000Å is reflected at nearly
5 The ratio of intensities of two waves is 9:1.If normal incidence from a soap films ofrefractive
they superimpose, the ratio of maximum to index 1.4. The least thickness of the film that will
minimum intensitywill be: appear black is : (2002/
(2000/ (b) 200¢
(a) 3:1 (b) 4:9 (a) infinity
(c) 2000 ¢ (d) 1000 ¢
(c) 4:1 (d) 1:9
Wave Optics -P-179
12. A ray of light is incident on the surface of plate
of glass of refractive index 1.5 at the polarising
angle. The angle of refractionof the ray will be: (a) |E
(a) 33. (b) 43.7 [2002/
(c) 23. (d) 53. t’
13. When a beam of light is used to determine the
position of an object, the maximum accuracy is
achieved if the light is: (2003]
(a) polarised (b) |E
(b) of longer wavelength
(c) of shorter wavelength
(d) ofhigh intensity
14. A double slit experiment is performed with light
of wavelength500 nm. Athis film ofthickness 2 (c) E
um and refractive index 1.5 is introduced in the
path of the upper beam. The location of the
central maximum will : |2003]
(a) remain unshifted
(b) shift downward by nearly two fringes
(d) |E
(c) shift upward by nearly two fringes
(d) shift downward by ten fringes
15. An astronaut is looking down on earth's surface 20. Two point white dots are I mm apart on a black
from a space shuttle an altitude of 400 km. paper. They are viewed by eye of pupildiameter
Assuming that the astronaut's pupil diameter is 3mm. Approximately, what is the maximum
5 mm and the wavelength of visible light is 500 distance at which these dots can be resolved by
nm, the astronaut will be able to resolve linear the eye? [Take wavelength of light - 500 nm]
objects of the size of about : (2003/ (a) Im (b) 5m [2008]
(a) 0.5m (b) Sm (c) 3m (d) 6m
(c) 50m (d) 500m 21. What happens to fringe width in Young's double
16. When a compact disc is illuminated by a source slit experiment if it is performed in glycerine
of white light, coloured lines are observed. This instead of air [2009/
is due to: (2004| (a) shrinks (b) disappears
(a) dispersion (b) diffraction (c) unchanged (d) enlarged
(c) interference (d) refraction 22. Ifa polaroid is kept in the path of an uniformly
17. In case oflinearly polarised light, the magnitude unpolarised light, the intensity of the transmitted
ofthe electric field vector: [2005] light to the intensity of the light when the
polaroid was not kept in its path is (2009)
(a) does not change with time 1
(b) varies periodically with time (a) 1 (b)
(c) increases and decreases linearly with time
1
(d) is parallel to the direction ofpropagation (d)
18. When exposed to sunlight, thin films of oil on
water often exhibit brilliant colours due to the 23. In a single slit diffraction experiment, the width
phenomenon of: |2005| of the slit is made double its original width. Then
(a) interference (b) difiraction the central maximum of the difraction pattern
will become (2009)
(c) dispersion (d) polarisation
(a) narrower and fainter
19. Which of the following diagrams represents the (b) narrower and brighter
variation of electricfield vector with time for a (c) broader and fainter
circulatory polarized light? (2006| (d) broader and brighter
 Topicwise AIIMS Solved Papers - PHYSICS
P-180}
24. Ifthe source of light used in a Young's double 29. Two sources of light of wavelengths 2500 Å
slit experiment is changed from red to violet: and 3500 ¢ are used in Young's double slit expt.
(a) the fringes will become brighter simultaneously. Which orders of fringes of two
[2011|
(b) consecutive fringes will comes closer wavelength patterns coincide? (2013/
(a) 3rd order of Ist source and 5th of the 2nd
(c) the intensity of minima will increase 7th order of l st and 5th order of 2 nd
(d) the central fringe- will became a dark fringe (b)
(c) Sth order of 1st and 3rd order of 2nd
25. Wavelength of light used in an optical instrument (d) Sth order of 1st and 7th order of2nd
are 2 =4000 A and A, = 5000 A, then 30. In Young's double slit experiment, we get 10
ratio of their respective resolving powers fringes in the field of view of monochromatic
(corresponding to .and 2,) is (2012/ light of wavelength 4000¢. If we use
(a) 16:25 (b) 9:1 monochromatic light of wavelength 5000Å, then
the number of fringes obtained in the same field
(c) 4:5 (d) 5:4
of view is [2014/
26. The correct formula for fringe visibility is
(a) 8 (b) 10
(a) V=max -min (2012/ (c) 40 (d) 50
max +min 31. The condition for obtaining secondary maxima
in the diftraction pattern due to single slit is
(b) V='max +Imin (a) a sin = nà 2014/
Lmax -Imin
(b) asin 0 =(2n -1)
(C) Vmax (c) asin =(2n-1)2
Imin
(d) asin = nà
(d) V= min 32. The Fraunhoffer diffiraction' pattern of asingle
max slit is formed in the focal plane ofa lens of focal
27. In Young's expt., the distance between two slits length l m. The width ofslit is 0.3 mm. Ifthird
d
minimum is formed at a distance of5 mm from
is
3
and the distance between the screen and central maximum, then wavelength of light will
be [2015)
(a) s000 ¢ (b) 2500 ¢
the slits is 3 D. The number of fringes in m on (c) 7500 ¢ (d) 8500¢
the screen, formed by monochromatic light of 33. Aparallel beam of monochromatic unpolarised
wavelength 32, will be (2012/ light is incident on a transparent diclectric plate
d of refractive index -.The reflected beam is
(a) (b)
9DÀ 27DA
completely polarised. Then the angle of
d d incidence is [2015/
(c) (d (b) 60
81 D D (a) 30
(c) 45° (d) 75°
28. To demonstrate the phenomenon of 34. A single slit Fraunhoffer diffraction pattern is
interference, we require two sources which emit formed with white light. For what wavelength
radiation of
of light the third secondary maximum in the
(a) nearly the same frequency [2013] diffraction pattern coincides with the second
(b) the same frequency secondary maximum in the pattern for red light
(c) different wavelengths of wavelength 6500 ¢? |2016|
(d) the same frequency and having a definite (a) 4400 ¢ (b) 4100¢
phase relationship (c) 4642.8 Å (d) 9100 Å
Wave Optics P-181
35. A diffraction pattern is obtaincd by using beam Reason : It happens due to the interference of
of red. light what will happen, if red light light reflected from the upper surface ofthe thin
replced by the blue light? (2017| film. [2002/
(a) Bands disappcar. 41. Assertion :At the first glance, the top surface
(b) Bands become broader and farther apart. of the Morpho butterfly's wing appears a
(c) No change will take place. beautiful blue-green. If the wind moves the
(d) Diffraction bands become narrow and colour changes.
crowded together. Reason : Different pigments in the wing reflect
TYPE B: ASSERTION REASON QUESTIONS light at different angles. [2004|
42. Assertion :A famous painting was painted by
Directions for (Qs. 36-48) : These questions consist not using brush strokes in the usual manner,
of two statements, cach printed as Assertion and but rathera myriad of small colour dots. In this
Reason. While answering these questions, you are painting the colour you see at any given place
required to choose any one of the following five on the painting changes as you move away.
responses.
(a) If both Assertion and Reason are correct and Reason : The angular separation ofadjacent dots
the Reason is a correct explanation of the changes with the distance from the painting.
|2004|
(b)
Assertion.
If both Assertion and Reason are correct but 43. Assertion : The clouds in sky generally appear
to be whitish.
Reason is not a correct explanation of the
Assertion. Reason : Diffraction due to clouds is efficient in
(c) If the Assertion is correct but Reason equal measure at all wavelengths. [2005/
incorrect. 44. Assertion : The resolving power of a telescope
d) If both the Assertion and Reason are incorrect. is more if the diameter of the objective lens is
(e) If the Assertion is incorrect but the Reason is more.
correct.
Reason: Objective lens oflarge diameter collects
36. Assertion :The colour ofthe green flower seen more light. [2005)
through red glass appears to be dark. 45. Assertion: Standard optical diffraction gratings
Reason : Red glass transmits only red light.
|1997| can not be uscd for discriminating between X
37 ray wavelengths.
Assertion : In Young's experiment, the fringe
width for dark fringes is different from that for Reason : The grating spacing is not of the order
white fringes. of X-ray wavelengths. (2006}
Reason : In Young's double slit experiment the 46. Assertion : Goggles have zero power.
fringes are performed with a source ofwhite light, Reason : Radius of curvature of both sides of
then only black and bright fringes are observed. lens is same. [2007]
[2001| 47. Assertion : A white source of light during
38. Assertion : Coloured spectrum is seen when we interference forms only white and black fringes.
look through a muslin cloth. Reason : Width of fringe is inversely
Reason : It is due to the diffraction of white
light on passing through fine slits |2002/ proportional to the wavelength of the light used.
(2007)
39. Assertion : When tiny circular obstacle is placed 48. Assertion : In Young's double slit experiment
in the path oflight from some distance, a bright
spot is seen at the centre of the shadow of the the two slits are at distance d apart. Interference
obstacle. pattern is observed on a screen at distance D
Reason : Destructive interference occurs at the from the slits. At a point onthe screen when it is
centre of the shadow. (2002/ directly opposite to onc of theslits, adark fringe
40, Assertion : Thin films sucha soap bubble or a is observed. Then, the wavelength of wave is
thin layer of oil on water show beautiful colours proportional to square of distance of two slits
when illuminated by white light. Reason: For a dark fringe intensity is zero. (2008/
P-182 Topicwise AIIMS Solved Papers - PHYSICS
Directions for (Qs. 49-51) : Each of thesequestions Reason : The fringe width is inversely
contains an Assertion followed by Reason. Read them proportional to the distance between the two
carefully and answer the question on the basis slits. (2009/
following options. You have to select the one that 50. Assertion :In Young's double slit experiment if
best describes the two statements. wavelength of incident monochromatic light is
(a) If both Assertion and Reason are correct and just doubled, number of bright fringe on the
screen will increase.
Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are correct, but Reason :Maximum number ofbright fringe on
the screen directly proportional to the
Reason is not the correct explanation of
Assertion. wavelength of light used. [2015)
(c) IfAssertion is correct but Reason is incorrect. 51. Assertion: Diffraction takes place for alltypes
of waves mechanical or non-mechanical,
(d) Ifboth the Assertion and Reason are incorrect. transverse or longitudinal.
49. Assertion: No interference pattern is detected
when two coherent sources are infinitely close Reason : Diffraction's effect are perceptible
to cach other. only if wavelength of wave is comparable to
dimensions of diffracting device. [2017|