DGT MH –CET 11th PHYSICS Study Material 1

Refraction of Light 1

08 Refraction of Light

Syllabus Refraction of light

8.0 Introduction
8.1 Refraction of monochromatic
light
8.2 Snell's law
8.3 Total internal reflection
8.4 Critical angle
8.5 Optical fibre
8.6 Dispersion of light
8.7 Prism and prism formula
8.8 Angular dispersion and dispersive Refraction of light is essentially a surface
power phenomenon governed by law of
conservation of energy and momentum.
8.9 Rainbow Due to change of medium, the phase velocity
8.10 Scattering of light of the wave is changed but its frequency
8.11 Blue colour of the sky remains constant.
8.12 Colour of the sun at sunrise and
sunset
8.13 Elementary idea of Raman effect

Formulae 2
iii. sin i C  
1. Absolute refractive index : 1

5. Prism angle :
c
 A= r1 + r2.
v 6. Angle of deviation :
2. Snell's law :  = i – r if i > r
 2 sin i 1 v1 7. The relation between i, e, A and  for prism:
12     i + e = A + .
1 sin r  2 v 2
8. For the minimum deviation (i = e) :
3. Relative refractive index :
A  m
1 i
i. 1  2   2
2 1 9. Angle of minimum deviation for thin prism :
2 m = A( – 1)
ii. 12  10. Mean deviation :
1
(1   2 )
iii. 12 × 23 × 31 = 1 
2
Re al depth
iv.   Apparent depth
11. Refractive index of material of the prism/
prism formula :
4. Critical angle :
 A  m 
1 v sin  
i. sin i C  ii. sin i C    2 
 c A
sin  
2

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Refraction of Light 2
12. For thin prism : 2. Maximum value of angle of refraction in rarer
 medium when ray travels from denser to rarer
 1 medium is 900.
A
3. The value of refractive index depends on the
13. Angular dispersion for red and violet rays:
nature and temperature of the two media and
(v – r) = A (v – r)
colour of light.
14. Mean refractive index for two colours :
4. A transparent solid is invisible in a liquid of same
1   2
 refractive index (because of no refraction).
2 5. When a glass slab is placed over a page in which
15. Dispersive power: letters are printed in different colours, the image
v  r v  r of all the letters will not lie in the same plane.
i.   y ii.     1 This is because, refractive index of glass is
y
different for different colours. Thus, images of
 2  1 different coloured letters are raised differently.

iii. ( 1  2 ) Shortcuts
1
2
1. If the distance travelled by a ray of light in two
16. Net angular dispersion without deviation :
media are s1 and s2 in the same time 't' then the
 ( – ')
ratio of refractive index of the 2nd medium to 1st
17. Net deviation without dispersion :
medium is given by
 
1   v1 s1
 '  1 2  
v2 s2
Notes 2. If the angle of minimum deviation is equal to the
1. Reflection involves change in the path of light refracting angle then we can directly use the
without any change in medium; whereas formula
refraction involves change in the path of light on
change in the medium. A
  2 cos
2. In case of refraction of light frequency (and 2
hence colour) and phase do not change (while 3. If dispersive power () and R.I. of two extreme
wavelength and velocity will change.) Also, the colours (say 1 and 2, 2 > 1) are given then to
intensity of incident light decreases as it goes from find the R.I. of mean colour (m) use the formula
one medium to another medium.
3. When a light ray travels from denser to rarer  2  1
m  1 
medium, it deviates away from normal while if it 
is travelling from rarer to the denser medium, it is
4. To deviate a ray through 900 or 1800 totally,
deviated towards the normal.
reflecting prism (450 – 900 – 450) are used which
4. Refractive index of vacuum is taken as 1.
uses phenomenon of total internal reflection.
5. All refractive indices are measured with respect
to air if other medium is not mentioned. Increase in diameter of the hole = d (t2 – t1)
6. Total internal reflection are measured with respect 5. Sometimes in the question, a portion of a prism
to air if other medium is not mentioned. with some of the angles is provided. In such a
7. The value of critical angle depends on the situation, one should first complete the figure for
refractive indices of the two media, colour of light prism and then use the procedure generally
and the temperature of the medium. applied to solve problems related to prism.
8. For Rayleigh's law; size of scattering particle is
much more smaller as compared to  of light.
9. Blue colour is scattered 16 times more than red
colour.
Mindbenders
1. If the incident angle and refracting angle both
are zero, then any ray is incident normally and
refracted into the medium II undeviated.

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Refraction of Light 3
c) only frequency of light changes
Facts about fiber optics d) velocity and wavelength of light changes but
frequency remains the same

8.1 Refraction of monochromatic light

4. The colour of light is determined by
a) velocity
b) medium through which it travels
c) frequency
d) time required to reach eye
5. LASER is a _______ .
a) monochromatic light
b) composite light
Fiber optics were needed because television c) white light
cables were becoming capable of carrying d) light from black body
more information than copper wire. So
computer and telephone companies needed 6. A wave of light of _______ wavelength is called
something to compete. monochromatic light.
The image above is of a light pipe. A light a) fixed velocity and
pipe is a bundle of optical fibres, with each b) mixed frequencies and
fibre thinner than a human hair. c) maximum
Since the pipe is flexible, it can be twisted in d) single
any desired manner and is used in medical
and optical examination of the inaccessible 7. When a ray of monochromatic light is incident
parts of human body. normally on glass surface then refracted ray
Optical fibres can transmit an image. They a) bends away from the normal
are used in transmission and reception of b) bends towards the normal
electrical signals by converting them first c) travels along the same path without any
into light signals. deviation
Optical fibres are used in telephone and
other transmitting cables. Currently all new d) will make an angle of 600 with the normal
undersea cables are made of optical fibers. 8. When a ray of monochromatic light is incident
Optical fiber phone lines are useful as they obliquely on the interface of two media
cannot be bugged or tapped. Each fibre can a) all the light is reflected back into same medium
carry upto 2000 telephone messages with only
almost no loss of intensity. b) all the light is transmitted (refracted) into other
By 21st century, 98% of copper wires will be medium
replaced by fibre optic cable.
c) only partial reflection takes place
d) part of light is reflected back into the same
medium
Multiple Choice Questions 9. When a monochromatic light passes from one
transparent medium into another, its direction
Classical Thinking changes (except for normal incidence). This
8.0 Introduction phenomenon is known as ______
1. Light consists of a) reflection of light
a) transverse electromagnetic waves b) refraction of light
b) transverse waves in a string c) polarisation of light
c) longitudinal waves d) diffraction of light
d) stationary waves 10. The angle made by the incident ray with the
2. For visible light the wavelength ranges from reflecting surface or interface is called as ____
a) 2600 Å to 7500 Å b) 3600 Å to 7500 Å a) angle of incidence
c) 3600 Å to 8500 Å d) 4600 Å to 9500 Å
b) angle of reflection
3. If medium changes
c) glancing angle
a) only velocity of light changes
b) only wavelength of light changes d) angle of refraction

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Refraction of Light 4
8.2 Snell's law 19. From the following ray diagram  and 1 are
11. The ray of light travelling from an optically denser
medium to optically rarer medium bends N1
P S
a) towards the normal
b) along the normal
1st medium
c) away from the normal 
X Q Y
d) by reversing its path nd
2 medium r 1
12. The bottom of a swimming pool appears to be
less deep than actual because of _______
a) reflection b) scattering N2 R
c) refraction d) diffraction
a) and 1 are glancing angle for reflection
13. A person swimming at the bottom of a swimming
b) and 1 are glancing angle for the refraction
pool looks up to the diving board. The board
c) and 1 are angle of deviation for reflection
a) is not seen at all d) is angle of deviation for reflection and 1 is
b) appears nearer angle of deviation for refraction
c) appears farther 20. The velocity of light is maximum in ______
a) alcohol b) water
d) appears at the correct position
c) vacuum d) glass
14. '1µ2' or '1n2' is called as 21. If the ray of light travels from medium 1 to
a) refractive index of 2nd medium with respect medium 2 and ultimately reverses its path then
to 1st medium the phenomenon is ______
b) refractive index of 1st medium with respect to a) principle of reflection
2nd medium b) principle of refraction
c) the relative refractive index of 1st medium c) principle of reversibility
d) principle of wave theory
d) absolute refractive index of 2nd medium
22. If the refractive indices of glass and water with
15. If µ1 and µ2 are absolute refractive index of
medium 1 and medium 2 respectively then 3 4
respect to air are and respectively. The
2 3
1 2 refractive index of glass with respect to water is
a) 1  2   b) 1  2  
2 1 [c = 3 × 108 m/s]
8 9
1 a) b)
c) 1µ2 = µ1µ2 d) 1 2  9 8
1 2
7 3
16. The absolute refractive index of any medium is c) d)
always 6 2
23. The refractive index of air with respect to glass
a) greater than one
is 2/3. The refractive index of diamond with
b) less than one respect to air is 12/5. Then, the refractive index
c) equal to one of glass with respect to diamond will be
d) any value between 0 to 1 5 8
17. The value of refractive index of _______ is a) b)
8 9
highest
5 18
a) ice b) water c) d)
18 5
c) diamond d) glass
24. A monochromatic ray is incident on a glass slab
18. When a ray of monochromatic light enters from with glancing angle 300 with the surface. If the
rarer medium to denser medium obliquely, the refractive index of glass with respect to air is
angle of incidence i and angle of refraction r is
related as 3 , the angle of refraction in the glass slab is
a) i < r b) i = r a) 300 b) 450
c) i > r d) both 'a' and 'b' c) 600 d) 700

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Refraction of Light 5
25. A monochromatic light of wavelength 4800 Å d) a reflected ray, a refracted ray with angle
travelling in air is incident on a glass slab of between them greater than (1800 – 2)
refractive index 1.5, its wavelength in glass slab 32. The principle used in optical fibre is ______
is a) scattering
a) 5000 Å b) 4800 Å b) successive reflections
c) 3500 Å d) 3200 Å c) refraction
26. The refractive index of water relative to air is d) total internal reflection
5/3. A ray of light passing from water into air is 33. In periscopes, totally reflecting prisms are used
incident at the interface at an angle of 320 with which turns the ray through
the normal. What angle does not the refracted a) 1800 b) 900
0
ray make with the normal ? c) 270 d) 450
a) 6102' b) 8 0
0
c) 62 2' d) 6001' 8.4 Critical angle
34. When a monochromatic ray of light travels from
8.3 Total internal reflection an optically denser medium to optically rarer
27. When the ray of light travels from an optically medium then critical angle is the angle of
denser medium to optically rarer medium the incidence for which angle of refraction is
maximum value of angle of refraction is a) 0 0 b) 450
a) 300 b) 450 c) 90 0
d) 1800
0
c) 60 d) 900 35. The angle of incidence corresponding to which
28. Which of the following is a CORRECT the angle of refraction is a right angle is called as
statement? a) angle of reflection b) angle of refraction
a) For total internal reflection, light must pass c) critical angle d) polarising angle
from optically denser medium to optically rarer 36. The critical angle iC is given by [µ is the refractive
medium with angle of incidence greater than index of optically denser medium with respect to
the critical angle air]
b) For total internal reflection, light must pass
1  1 
from optically rarer medium to optically denser a) iC = sin–1(µ) b) i C  sin  
medium with angle of incidence greater than 
the critical angle
1 1 1  1 
c) For total internal reflection, light must pass c) i C  sin   d) i C  2 sin  
from optically denser medium to optically rarer 2 
medium with angle of incidence less than 37. Critical angle of light passing from glass to air is
critical angle. minimum for
d) For total internal reflection, only medium plays a) red b) green
a role and not angle of incidence c) yellow d) violet
29. 'Mirage' is a phenomenon due to 38. The refractive index of medium with respect to
a) reflection of light air, for the critical angle 600 is
b) refraction of light a) 1.6 b) 1.5
c) total internal reflection of light c) 1.2 d) 1.15
d) diffraction of light
30. Which of the following is NOT a property of light? 8.5 Optical fibre
a) It requires a material medium for propagation 39. An endoscope is used by a physician to view the
b) It shows a rectilinear propagation internal parts of a body organ. It is based on the
c) It involves transportation of energy principle of _____
d) It has finite speed a) refraction b) total internal reflection
31. A ray of light travelling in water is incident on its c) reflection d) dispersion
open surface in air. The angle of incidence is 0, 40. Optical fibre consists of large number of
which is less than the critical angle. Then there a) extremely thin fibres of fine quality glass or
will be quartz
a) only reflected ray and no refracted ray b) extremely thin fibres of metal with high
b) only refracted ray and no reflected ray ductility
c) a reflected ray, a refracted ray with angle c) extremely fine fibres of wood with very high
between them less than (1800 – 2) polished surface
d) thick fibres of fine quality glass or quartz

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Refraction of Light 6
41. When a light is incident at one end of the fibre at
a small angle, then refracted light falls on the wall
of the fibre at an angle
a) equal to critical angle
b) greater than 900
c) equal to 00 b)
d) greater than critical angle
42. The light entering into the fibre suffers
a) number of reflections
b) total internal reflections
c) number of refractions
d) multiple refractions
43. If I is the intensity of light entering into the optical
firbe and Ic is that emerging from the fibre then c)
a) I  I c b) I << Ic
1
c) I >> Ic d) I c 
2

8.6 Dispersion of light

44. The separation of white light into its constiuent
colours after passing through a prism is called as d)
_____ of light
a) deviation b) refraction
c) scattering d) dispersion 49. When white light passes through prism, the angle
45. When white light passes through prism then of deviation is
constituent colours are obtained because a) maximum for red and minimum for violet
a) different colours are due to different velocities b) maximum for yellow and minimum for red
and different wavelengths c) maximum for yellow and minimum for violet
b) different colours are due to same velocity and d) minimum for red and maximum for violet
different wavelengths 50. As the refractive index of the material of prism
c) different colours are already present in prism for different colours increases their corresponding
d) same colour appears different due to different wavelength _______
frequency in another medium a) decreases b) increases
46. A prism splits a beam of white light into its c) remains the same d) depends on frequency
constituent colours. This is because 51. The ratio of the refractive index of red light to
a) phase of different colour is different that of blue light in air is _______
b) amplitude of different colours is different a) less than unity
c) energy of different colours is different b) equal to unity
d) velocity of different colours is different c) greater than unity
47. The refractive index of glass is minimum for d) less or greater than unity, depending upon the
a) red light b) green light experimental arrangement
c) yellow light d) violet light
48. Dispersion of light is shown in the following 8.7 Prism and prism formula
diagram, select the correct one 52. A _______ shaped triangular transparent block
having three rectangular planes and two triangular
planes is called a prism
a) wedge b) hexagonal
c) polygonal d) ellipsoidal
53. The angle between the two plane rectangular
a) refracting surface is called ______
a) refracting angle of the prism
b) angle of refraction
c) reflecting angle of the prism
d) dispersion angle

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Refraction of Light 7
54. The rectangular face opposite to the refracting 63. A ray is incident at an angle of incidence 'i' on
edge is called ______ one surface of a prism of small angle A and
a) refracting surface emerges normally from the opposite surface. If
b) base of prism the refractive index of the material of the prism
c) intersection of base and one of the refracting is µ, the angle of incidence 'i' is nearly equal to
surface
A A
d) principle section of a prism a) b)
55. The angle between incident ray and _____ ray  2
is called angle of deviation
A
a) reflected b) refracted c) µA d)
c) emergent d) normal 2
56. The relation between i, e, A and  for prism is
8.8 Angular dispersion and dispersive power
A
a) i  e  b) i = A + + e 64. A narrow beam of white light passes through glass
2 slab having parallel faces. Then,
c) A = i + e +  d) i + e = A + 
a) the beam inside the slab remains as white light
57. While deriving prism formula, angle of deviation
b) the emergent beam is red in colour
is minimum if
a) angle of incidence is equal to angle of deviation c) the beam inside the slab undergoes dispersion
b) angle of incidence is equal to angle of d) the glass slab never causes dispersion
refraction 65. Angular dispersion depends upon
c) angle of incidence is equal to refracting angle a) refracting angle of the prism
of prism b) refractive index of the prism
d) angle of emergence and angle of incidence c) velocity of light in the prism
are equal d) both 'a' and 'b'
58. Thin prism has small _______ 66. The net angular dispersion produced without
a) angle of incidence b) refractive index deviation for crown glass (µ = 1.56) and flint glass
c) angle of reflection d) refracting angle (µ = 1.7) is
59. For thin prism angle of minimum deviation () is
a) positive b) zero
given by
c) negative d) infinite
  67. The refractive index of glass is 1.520 for red light
a) = A (1 – µ) b)   A  1
2  and 1.525 for blue light. Let r and b be the angle
of minimum deviation for red and blue light
  respectively in a prism of thin glass, then
c)   A1   d) = A (µ – 1)
 2 a) r = b b) r > b
60. A prism of angle 40 gives a deviation of 2.40. The c) r < b d) both 'a' and 'b'
refractive index of the material of the prism is 68. The angular dispersion produced by a prism of
a) 1.5 b) 1.55 angle 50 is [µv = 1.665, µr = 1.645]
c) 1.6 d) 1.8 a) 2 0 b) 1 0
61. The refractivity of the material of the prism is c) 0.20 d) 0.10
given by
69. The dispersive power () of the material of prism
1 is given by
a) µ b)

A ( v   r ) ( v   r )
a)   ( y  1) b)   A (  1)
1 y
c) d) (µ – 1)
2
( v   r ) ( v   r )
62. A glass prism placed in a homogeneous transparent c)   (  1) d)   (  1)
medium will deviate an incident ray y y

a) always towards its base 70. The refractive index of the prism for violet colour
b) always away from its base is 1.7 and that for red is 1.65. Then dispersive
c) towards its base, only if the medium has a power of the material of prism is
refractive index greater than that of glass a) 0.74 b) 0.074
d) towards the base, only if the medium has a c) 0.054 d) 0.015
refractive index less than that of glass

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Refraction of Light 8
71. The net angular dispersion without deviation is 80. Angular width of primary rainbow is
equal to a) 2 0 b) 3 0
0
c) 5 d) 6 0
   ' 
a) 1   b) 1   81. The average angle of inclination of the primary
 '    rainbow with the axis is
c) ('– ) d) ( – ') a) 400 b) 410
72. The arrangement of dispersion without deviation c) 420 d) 430
is used in _______ 82. In case of secondary rainbow, ______ colour is
a) direct vision spectroscopy at the top.
b) indirect spectroscopy a) red b) orange
d) binocular vision c) violet d) pink
d) periscope 83. The secondary rainbow is due to ______ total
73. In optical instruments, to minimise the effect of internal reflection inside droplet
dispersion and obtain clear and well defined a) one b) two
images c) three d) four
a) three prisms are used side by side 84. The straight line joining the sun and the observer
b) achromatic combination of prisms are used along which centre of both the primary and
c) chromatic combination of prisms are used secondary rainbow lies is called
d) two prisms of different glasses and same angle a) axis of rainbow
of prism is used b) principle line of rainbow
74. A thin prism P1 with refracting angle 40 and made c) radius of primary rainbow
from glass of refractive index 1.54 is combined d) radius of secondary rainbow
with another prism P2 made from glass of refractive
index 1.72, with vertex opposite to P1 to produce 8.10 Scattering of light
dispersion without deviation. The angle of prism 85. One cannot see through fog, because
P2 is a) fog absorbs light
a) 2.60 b) 3 0 b) the refractive index of fog is infinity
0
c) 4 d) 5.330 c) light suffers total internal reflection at the
droplets in fog
8.9 Rainbow d) light is scattered by the droplets in fog
75. The first explanation of rainbow was given by 86. According to Rayleigh's law the intensity of
a) Rayleigh b) Demini scattered light is
c) Huygen d) Newton a) directly proportional to the wavelength of light
76. The rainbow is formed due to b) inversely proportional to the wavelength of
a) scattering of sun light by water droplets light
b) refraction and total internal reflection by water c) inversely proportional to the square of the
droplets wavelength of light
c) dispersion, reflection and refraction of sun light d) inversely proportional to the fourth power of
by water droplets the wavelength of light
d) only reflection and refraction by water droplets 87. Rayleigh's law of scattering assumes
77. The complete circle of rainbow can be seen when a) scattering of light by extremely small particles
a) the sun and observer are co-axial b) scattering of light by particles of twice the size
b) the observer and clouds are co-axial of the particle
c) the sun, the observer and clourds are co-axial c) scattering of light by very large particles
d) the sun and clouds are co-axial d) scattering of light by dust particles only
78. To observe any rainbow the altitude of sun or the
angle made by the sun with the horizontal should be 8.11 Blue colour of the sky
a) less than 420 88. The sky will appear red instead of blue if
b) greater than 420 a) atmospheric particles scatter blue light more
c) between 450 to 500 than red light
d) between 600 to 630 b) atmospheric particles scatter all colours equally
79. The primary rainbow is due to _____ total internal c) atmospheric particles scatter red light more
reflection inside droplet and two refractions than blue light
a) one b) two d) scattering does not take place
c) three d) infinite

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Refraction of Light 9
89. Beyond the earth's atmosphere, the sky will look 98. A yellow light travels from rarer medium to denser
a) dark (black) because there is no scattering medium. At the value of critical angle, the ray
b) white only because there is equal scattering will
c) blue because there is medium scattering a) graze along the surface with angle of refraction
d) violet because there is maximum scattering of 900
b) be reflected back only
8.12 Colour of the sun at sunrise and sunset c) be dispersed into another medium
90. Just after the sunrise, the sun is very close to d) be refracted into denser medium
horizon, so the sunlight has to travel 99. Which of the following is the CORRECT
a) longer path through the atmosphere to reach statement ?
the observer a) The dispersive power depends upon the angle
of prism
b) shorter path through the atmosphere to reach
b) The angular dispersion depends upon the
the observer
refracting angle of the prism
c) through cold atmosphere of the earth
c) The angular dispersion does not depend upon
d) through hot atmosphere of the sun
the dispersive power
91. The sun appears reddish or orange reddish at the
d) The dispersive power in vacuum is one
a) sunset b) mid day 100. A completely transparent material will be invisible
c) sunrise d) both 'a' and 'c' in vacuum when its refractive index µ is _____
92. Our eyes are more sensitive to blue as compared a) unity b) more than unity
to _______ c) less than unity d) equal to 1.33
a) yellow b) violet
c) pink d) white Critical Thinking
8.2 Snell's law
8.13 Elementary idea of Raman effect 1. Assertion : The frequencies of incident,
93. Sir C. V. Raman was awarded Nobel prize for reflected and refracted beam of monochromatic
his work concerned with which of the following light incident from one medium to another are
phenomenon of radiation ? same.
a) scattering b) diffraction Reason : The incident, reflected and refracted
c) interference d) polarisation rays are coplanar.
94. In Raman scattering there a) Assertion is True, Reason is True; Reason is
a) is increase in wavelength a correct explanation for Assertion.
b) is decrease in wavelength b) Assertion is True, Reason is True; Reason is
c) are both increase and decrease in the not a correct explanation for Assertion
wavelength c) Assertion is True, Reason is False
d) is no change in wavelength d) Assertion is False, Reason is True
2. If iµj represents refractive index when a light ray
Miscellaneous goes from medium i to medium j, then the product
95. The angle between incident ray and reflected ray µ × 3µ2 × 4µ3 is equal to
2 1

or refracted ray is called _______ a) 3µ1 b) 3µ2

a) respective angle of deviation 1
b) angle of minimum deviation c)  d) 4µ2
1 4
c) glancing angle
3. Rays of light fall on a glass plate, the refractive
d) emergence angle
index of which is µ. If the angle between the
96. When a ray of light passes from air to denser
reflected and refracted rays is 900, then the angle
medium, its speed is reduced by 30%. What is
of incidence is
the refractive index of the medium ?
a) sin–1 (µ) b) cos–1 (µ)
a) 1.33 b) 1.43 –1
c) tan (µ) d) tan–1 (1/µ)
c) 1.5 d) 1.1 4. To an observer on the earth, the stars appear to
97. A light of wavelength 6500 Å in air is passed twinkle. This can be ascribed to
through water of refractive index 1.3. The a) the fact that stars do not emit light continuously
percentage change in wavelength will be nearly b) frequency absorption of star light by their own
a) 15% b) 23% atmosphere
c) 25% d) 30%

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Refraction of Light 10
c) frequency absorption of star light by the earth's c) reflected light gradually increases and that
atmosphere of refracted light decreases
d) the refractive index fluctuations in the earth's d) reflected light and refracted light both
atmosphere decreases
5. A glass slab is placed in the path of a beam of 11. Light travels from a medium of refractive index
convergent light. The point of convergence of µ1 to another of refractive index µ2 (µ1 > µ2). For
light total internal reflection of light, which is NOT true?
a) moves towards the glass slab a) Light can be travel from medium of refractive
b) moves away from the glass slab index µ1 to µ2.
c) remains at the same point b) Angle of incidence must be greater than the
d) undergoes a lateral shift critical angle
6. A man standing in a swimming pool looks at a c) There is no refraction of light
stone lying at the bottom. The depth of the d) Light can travel from the medium of refractive
swimming pool is h. At what distance from the index µ2 to µ1.
surface of water is the image of the stone
12. A diver in a swimming pool wants to signal his
formed? (Line of vision is normal; Refractive
distress to a person lying on the edge of the pool
index of water is n)
by flashing his water proof flash light then,
a) h/n b) n/h
a) he must direct the beam vertically upwards
c) h d) hn
b) he has to direct the beam horizontally
7. A bucket completely full of water is 46 cm deep.
A coin kept at the bucket when viewed normally c) he has to direct the beam at an angle to the
vertical which is slightly less than the critical
 4 angle of incidence
will appear at   w  
 3 d) he has to direct the beam at an angle to the
a) 40 cm b) 34.5 cm vertical which is slightly more than the critical
c) 39 cm d) 32 cm angle of incidence
8. In fish in water (refractive index n) looks at a
bird vertically above in the air. If y is the height 8.4 Critical angle
of the bird and x is the depth of the fish from the 13. A ray of light travelling inside a rectangular glass
surface, then the distance of the bird as estimated block of refractive index 2 is incident on the
by the fish is glass-air surface at an angle of incidence of 450.
 1  1 The refractive index of air is one. Under these
a) x  y1   b) y  x1   conditions, the ray
 n  n
a) will emerge into the air without any deviation
 1 b) will be reflected back into the glass
c) x  y1   d) x + ny
 n c) will be observed
8.3 Total internal reflection d) will emerge into the air with an angle of
9. A, B, C in the diagram represent rays of light refraction equal to 900
incident upon a face of a right-angled prism. 14. With respect to air, critical angle in a medium for
Before emerging from the prism, which ray (or light of red colour [1] is . Other facts remaining
rays) will experience total internal reflection ? same, critical angle for light of yellow colour [2]
will be
450 a)  b) more than 

A 1
c) less than  d) 
450 2
B
C
8.6 Dispersion of light
a) ray A b) ray B
15. During dispersion of white light by prism placed
c) ray C d) ray A and C
in air, for a particular value of angle of prism
10. As 'i' increases, intensity of
a) only angular spread takes place
a) reflected light gradually decreases and that
b) only angular deviation takes place
of refracted light increases
b) reflected and refracted light increases c) both angular deviation and angular spread take
place

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Refraction of Light 11
–1 –1
d) for a particular value of angle of prism, either a) sin (0.6) b) sin (0.7)
of angular deviation for mean colour or spread c) sin–1 (0.75) d) sin–1 (0.8)
takes place 23. A ray of light is incident at an angle of 600 on one
16. When a white light passes through a hollow prism, face of a prism of angle 300. The emergent ray
then there is of light makes an angle of 300 with incident ray.
a) no dispersion and no deviation The angle made by emergent ray with second
b) dispersion but no deviation face of prism will be
c) deviation but no dispersion a) 0 0 b) 900
0
d) dispersion and deviation both c) 45 d) 300
24. The critical angle between an equilateral prism
8.7 Prism and prism formula and air is 450. If the incident ray is perpendicular
17. A given ray of light suffers minimum deviation in to the refracting surface, then
an equilateral prism P. Additional prisms Q and R a) after deviation it will emerge from the second
of identical shape and of same material as P are refracting surface
now added as shown in the figure. The ray will b) it is totally reflected on the second surface
now suffer and emerges out perpendicularly from third
surface in air
Q c) it is totally reflected from the second and third
P R refracting surfaces and finally emerges out
from the first surface
a) greater deviation d) it is totally reflected from all the three sides of
b) no deviation prism and never emerges out
c) same deviation 25. If the critical angle for the material of a prism is
d) total internal reflection C and the angle of the prism is A, then there will
18. A prism is placed in water. The angle of minimum be no emergent ray when
deviation _______ . a) A < 2 C b) A = 2 C
a) increases C
b) remain the same c) A > 2 C d) A 
2
c) decreases 26. A ray of light is incident normally on one face of
d) depends on frequency of incident light a prism of refracting angle A. After travelling
19. A ray of light is incident on a 600 prism at the through prism, the ray emerges from the second
minimum deviation position. The angle of refracting surface making an angle of deviation
refraction at the first face (i.e. incident face) of of . The refractive index of the material of prism
the prism is is
a) zero b) 300
c) 450 d) 600 A
sin 
20. A prism having refractive index 2 and  2  sin A
refracting angle 300, has one of the refracting a) A b)
sin   sin 
surfaces polished. A beam of monochromatic light 2
incident on the other refracting surface will
retrace its path if the angle of incidence is sin  sin(A  )
a) 0 0 b) 300 c) d) sin(A)
0
sin A
c) 45 d) 600
27. A light ray is incident upon a prism in minimum
21. A monochromatic ray of light travels through an
deviation position and suffers a deviation of 340.
equilateral prism such that angle of deviation is
If the shaded half of the prism is knocked off, the
300. If the difference between angles of incidence
ray will
and emergence is 100, then i and r respectively
are
a) 450, 550 b) 500, 400
0 0
c) 35 , 45 d) 300, 400
22. A ray of light is incident on a refracting face of
glass prism of refracting angle 300. If the ray
emerges normally from the second refracting
a) suffer a deviation of 340
surface, the angle of incidence is [aµg = 1.5]
b) suffer a deviation of 680

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Refraction of Light 12
0
c) suffer a deviation of 17 b) two points propagating in two different parallel
d) not come out of the prism directions
28. The refractive index of a glass is 1.520 for red c) one point propagating in two different directions
light and 1.525 for blue light. Let D1 and D2 be d) one point propagating in same directioin
the angles of minimum deviation for red light and 33. The figure shows the view through the eye-piece
blue light respectively in a prism of this glass. of a prism spectrometer with its slit illuminated
Then by the source of light emitting three wavelengths
a) D1 > D2 corresponding to yellow (Y), green (G) and
b) D1 = D2 unknown colour (X). The colour x may be ____
c) D1 < D2
d) D1 can be less than or greater than D2
depending upon the angle of prism
29. The ratio of angle of minimum deviation of a prism
3
in air and when dipped in water will be a  g  X GY
2
9
and w g  a) red b) orange
8 c) pink d) indigo
1 1 34. When a glass prism is placed inside water, its
a) b) dispersive power _______
8 2
a) decreases
3 1 b) remains the same
c) d)
4 4 c) increases
30. For a small angled prism, angle of prism A, the d) may increase or decrease depending on
angle of minimum deviation () varies with the refracting angle of prism
refractive index of the prism as shown in the graph 35. Angle of minimum deviation for a prism of
refractive index 1.5, is equal to the angle of the
 prism. Then the angle of the prism is
Q
(cos 410 = 0.75)
a) 620 b) 410
0
c) 52 d) 310
O P  36. The angle of minimum deviation of a prism of
a) Point P corresponds to µ = 1 refractive index 3 is equal to its refracting
b) Slope of the line PQ = A/2 angle. Then the refracting angle of that prism is
c) Slope of the line PQ = A a) 300 b) 450
d) Both 'a' and 'c' are true c) 60 0
d) 900
31. The angle of the prism is A and if the angle of 37. Two prisms of different materials and angles are
minimum deviation is (1800 – 2A) then the used to give dispersion without deviation. Which
refractive index of the material of prism is of the following statemet is true ?
a) The order of colours of the spectrum in
A A
a) cos  b) sin   combination is reversed
2 2 b) The order of colours of the spectrum in
combination remains the same
A A
c) tan  d) cot  c) The mean colour is absorbed after the rays
2 2 emerges from combination
d) Only order of first colour (or red colour) is
8.8 Angular dispersion and dispersive power changed, other colours remain same
32. A beam of light composed of red and green rays 38. To produce deviation without dispersion with the
is incident obliquely at a point on the face of help of crown glass prism of refracting angle (A)
rectangular glass slab. When coming out on the and filnt glass prism (A') they must be related as
opposite parallel face, the red and green rays a) A > A' b) A = A'
emerge from
A'
a) two points propagating in two different non- c) A < A' d) A 
parallel drections 2

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Refraction of Light 13
0
39. A crown glass prism of refracting angle 6 is to 45. The distance travelled by a ray of light in two
be achromatised for red and blue light using a media, in the same time are in the ratio 2 : 3. The
flint glass prism. The angle of second prism and ratio of refractive index of the first medium to
net deviation is second medium is
[For crown glass µr = 1.520, µb = 1.531 and for a) 3 : 2 b) 4 : 9
flint glass µr' = 1.662, µb' = 1.684] c) 2 : 3 d) 9 : 8
a) 90, 1.134' b) 60, 2.2680 46. A small bulb is placed at the bottom of a tank
0 0
c) 3 , 3.334 d) 30, 1.1340 containing water to a depth of 80 cm. What is
40. If the refractive indices of crown glass for red, the area of the surface of water through which
yellow and violet colours are 1.5140, 1.5170 and light from the bulb can emerge out ? Refractive
1.5318 respectively and for flint glass these values index of water is 1.33. (Consider the bulb to be a
are 1.6434, 1.6499 and 1.6852 respectively, then point source)
the dispersive powers for crown and flint glass a) 3.13 m2 b) 1.43 m2
are respectively c) 2.61 m 2
d) 0.88 m2
a) 0.034 and 0.064 b) 0.064 and 0.034 47. A tank is filled with water to a height of 12.5 cm.
c) 1.00 and 0.064 d) 0.034 and 1.0 The apparent depth of a needle lying at the bottom
41. The dispersive power of crown and flint glasses of the tank is measured by a microscope to be
are 0.03 and 0.05 respectively. The refractive 9.4 cm. What is the refractive index of water ?
indices for yellow light for these glasses are 1.517 If water is replaced by a liquid of refractive index
and 1.621 respectively. It is desired to form an 1.63 upto the same height, by what distance would
achromatic combination of prism of crown and the microscope have to be moved to focus on the
flint glasses which can produce a deviation of 10 needle again ?
in the yellow ray. Select right statement from the a) 1.33, 1.7 cm b) 1.7, 1.33 cm
following c) 1.33, 7.7 cm d) 1.7, 7.7 cm
a) refracting angle of crown glass is 4.80 and
48. A vessel of depth 2d cm is half filled with a liquid
that of flint glass is 2.40.
of refractive index µ1 and the upper half with a
b) refracting angle of crown glass is 2.40 and liquid of refractive index µ2. The apparent depth
that of flint glass is 4.80. of the vessel seen perpendicular is
c) refracting angle of both the glasses is 4.80 each
d) refracting angle of both the glasses is 2.40 each  1 2   1 1 
a) d     b) d    
 1 2   1 2 
8.13 Elementary idea of Raman effect
42. Raman line lies in ______  1 1   1 
a) infra-red region b) microwaves region c) 2d     d) 2d   
 1 2   1 2
c) ultraviolet region d) visible region
49. A layer of oil 3 cm thick is flowing on a layer of
coloured water 5 cm thick. Refractive index of
Miscellaneous
43. A ray of monochromatic light is incident on one 5
coloured water is and the apparent depth of
refracting face of a prism of refracting angle 750. 3
It passes through the prism and is incident on the
36
other face at the critical angle. If the refractive the two liquids appears to be cm. What is the
7
index of the material of the prism is 2 , the angle
refractive index of oil ?
of incidence on the first face of the prism is
a) 1.4 b) 2
a) 0 0 b) 300
0
c) 2.4 d) 3
c) 45 d) 600
50. In the given figure, the principal section of a glass
44. A ray of light passing through a prism having
prism is an isosceles triangle ABC with AB = AC.
refractive index 2 suffers minimum deviation. The face AC is silvered. A ray incident normally
It is found that the angle of incidence is double on face AB after two reflections, emerges from
the angle of refraction within the prism. Then the base BC in a direction perpendicular to it.
angle of prism is What is the angle  BAC of a prism ?
a) 450 b) 600
0
c) 75 d) 900

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Refraction of Light 14
space, and µ the corresponding quantities in a
medium, the refractive index of the medium is
 
a)  00 b)  
0 0

 00  0
c) d)  0

56. On heating a liquid, the refractive index generally
a) 30 0
b) 36 0 a) decreases
c) 600 d) 720 b) increases or decreases depending on the rate
51. The deviation produced by a thin glass prism place of heating
in air, when immersed in water is c) does not change
[Given aµg = 3/2 and aµw = 4/3] d) increases

a) reduces to one fourth 57. If i denotes a unit vector along incident light
b) reduces to half

c) remains the same ray, r a unit vector along refracted ray into a
d) increases four times 
medium of refractive index µ and n unit vector
52. A fish at a depth of 7 cm below the surface of
normal to boundary of medium directed towards
water sees the outside world through a circular
incident medium, then law of refraction is
horizon. What is the radius of the circular horizon?
       
 4 a) i . n  ( r . n ) b) i  n  (n r )
 a w  3 
         
c) i  n  ( r n ) d) ( i  n )  r n
a) 4 cm b) 3 cm
58. A ray of light passes through four transparent
c) 7 cm d) 1 cm
media with refractive indices µ1,µ2,µ3 and µ4 as
53. A ray of light is incident normally on one of the shown in the figure. The surface of all media are
faces of a prism of apex angle 300 and refractive parallel. If the emergent ray CD is parallel to the
index 2 . The angle of deviation through prism incident ray AB, we must have
is
a) 150 b) 300 D
c) 450 d) 600 µ4
54. A light ray is incident normally on the face AB of µ2 µ3
µ1 C
a right angled prism ABC (µ = 1.50) as shown in B
the figure. What is the largest angle  for which
the light ray is totally reflected at the face AC ? A

A a) µ1 = µ2 b) µ2 = µ1
c) µ3 = µ4 d) µ4 = µ1
59. The fine powder of a coloured glass is seen as
a) coloured
b) white
c) that of the glass colour

B C d) black
60. A circular disc of which 2/3 part is coated with
1  2  1  2  yellow and 1/3 part is with blue. It is rotated about
a)   sin   b)   cos   its central axis with high velocity, then it will be
3  3
seen as
1  1  1  2  a) green b) blue
c)   cos   d)   cot   c) white d) yellow
3  3
61. Light enters at an angle of incidence in a
55. If  0 and µ 0 are respectively, the electric
transparent rod of refractive index n. For what
permittivity and the magnetic permeability of free
value of the refractive index of the material of

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Refraction of Light 15
the rod the light once entered into it will not leave 65. Immiscible transparent liquids A, B, C, D and E
it through its lateral face whatsoever be the value are placed in a rectangular container of glass with
of angle of incidence ? the liquids making layers according to their
a) n  2 b) n = 1 densities. The refractive index of the liquids are
shown in the adjoining diagram. The container is
c) n = 1.1 d) n = 1.3
illuminated from the side and a small piece of
62. A glass prism (µ = 1.5) is dipped in water
glass having refractive index 1.61 is gently
(µ = 4/3) as shown in figure. A light ray is incident
dropped into the liquid layer. The glass piece as it
normally on the surface AB. It reaches the
descends downwards will not be visible in
surface BC after total reflection, is
A 1.51
B A B 1.53

C 1.61
D 1.52
E 1.65
C
a) liquid A and B only
a) sin  > 8/9 b) 2/3 > sin < 8/9
b) liquid C only
c) sin < 2/3 d) It is not possible c) liquid D and E only
63. An isosceles prism of angle 1200 has a refractive d) liquid A, B, D and E
index of 1.44. Two parallel monochromatic rays
enter the prism parallel to each other in air is Competitive Thinking
shown. The rays emerging from the opposite
8.2 Snell's law
faces
1. The refractive index of water and glass with
respect to air is 1.3 and 1.5 respectively, what
will be the refractive index of glass with respect
to water ?
0
120 1.5 1.3
a) b)
1.3 1.5
1 .5 1.6
c) d)
a) are parallel to each other 2.6 1.5
b) are diverging 2. A light of wavelength 6000 Å travels from rarer
c) make an angle 2 sin–1(0.72) with each other medium to denser medium of refractive index 1.5.
d) make an angle 2 [sin–1(0.72) – 300] with each If its frequency in rarer medium is 5 × 1014 Hz,
other then its frequency in denser medium will be
64. When light is incident on a medium at angle i and a) 3.3 × 1014 Hz b) 5 × 1014 Hz
7
refracted into a second medium at an angle r, the c) 2.5 × 10 Hz d) 7.5 × 1014 Hz
graph of sin i vs sin r is as shown in the graph. 3. If light travels from vacuum to water, its
From this, one can conclude that wavelength
a) increases
b) remains constant
sin r c) decreases
0 d) may increases or decreases
30
4. A ray of light is incident on a glass plate of
sin i
refractive index 1.5. The angle between the
a) velocity of light in the second medium is 1.73 reflected and refracted rays is 900. What is the
times the velocity of light in the I medium ratio of wavelength of reflected to refracted rays?
b) velocity of light in the I medium is 1.73 times a) 2.1 b) 1.5
the velocity in the II medium c) 1.6 d) none of these
c) the critical angle for the two media is given 5. A beam of monochromatic blue light of wavelength
by 450 4200 Å in air travels in water of refractive index
1 4/3. Its wavelength in water will be
d) sin i C  a) 4200 Å b) 5800 Å
2
c) 4150 Å d) 3150 Å

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Refraction of Light 16
14
6. A wave of light having frequency 4 × 10 Hz 15. A ray of light strikes a transparent rectangular
and speed of light 3 × 108 m/s enters glass of R.I. slab (of refractive index 2 ) at an angle of
1.5. Change in wavelength is
incident of 450. The angle between he reflected
a) 2.5 × 10–7 b) 2.5 × 10–6
–8
and refracted rays is
c) 2.5 × 10 d) 2.5 × 10–9
a) 750 b) 900
7. Light enters from air into a medium of R.I. 1.5. 0
c) 105 d) 1200
Percentage change in its wavelength is
16. A plane glass slab is kept over various coloured
a) 66.66% b) 50%
letters. Letter which appears least raised is
c) 33.33% d) 25%
8. The velocity of light in glass is 2 × 108 m/s. If a) blue b) violet
refractive index of glass with respect to water is c) green d) red
9/8, then the velocity of light in water is 17. A ray of light is incident on the surface of a glass
a) 1.6 × 108 m/s b) 1.33 × 108 m/s plate of thickness t. If the angle of incidence  is
8
c) 3 × 10 m/s d) 2.25 × 108 m/s small, the emerging ray would be displaced side
9. The ratio of velocities of light in glass to that in ways by an amount [take n = refractive index of
water is (refractive index of glass = 1.5 and glass]
refractive index of water = 1.33) a) tn/(n + 1) b) t(n – 1)/n
a) 0.8803 : 1 b) 0.8989 : 1 c) tn/(n – 1) d) t(n + 1)/n
c) 0.8867 : 1 d) 0.8504 : 1
8.3 Total internal reflection
3
10. Refractive index of glass is and refractive 18. For total internal reflection to take place, the angle
2 of incidence i and the refractive index µ of the
4 medium must satisfy the inequality
index of water is . If the speed of light in glass
3 1 1
a)  b) 
is 2.00 × 108 m/s, the speed in water will be sin i sin i
a) 2.67 × 108 m/s b) 2.25 × 108 m/s c) sin i < µ d) sin i > µ
8
c) 1.78 × 10 m/s d) 1.50 × 108 m/s 19. Assertion : Diamond glitters brilliantly.
11. Refractive index of glass with respect to medium Reason : Diamond does not absorb sunlight.
4 a) Assertion is True, Reason is True; Reason is
is . If vm – vg = 6.25 × 107 m/s, then velocity of a correct explanation for Assertion.
3
light in medium is b) Assertion is True, Reason is True; Reason is
a) 2.25 × 108 m/s b) 1.5 × 107 m/s not a correct explanation for Assertion
c) 2.25 × 10 m/s8
d) 4.5 × 107 m/s c) Assertion is True, Reason is False
12. A ray of light is incident on the surface of d) Assertion is False, Reason is True
separation of a medium at an angle 450 and is 20. Critical angle of light passing from glass to air is
refracted in the medium at an angle 300. What minimum for
will be the velocity of light in the medium ? a) red b) green
a) 1.96 × 108 m/s b) 2.12 × 108 m/s c) yellow d) violet
8
c) 3.86 × 10 m/s d) 3.33 × 188 m/s 21. The critical angle for total internal reflection in
13. A thin oil layer floats on water. A ray of light diamond is 24.50. The refractive index of the
making an angle of incidence of 400 shines on oil diamond is
layer. The angle of refraction of light ray in water a) 2.41 b) 1.41
is [µoil = 1.45, µwater = 1.33] c) 2.59 d) 1.59
a) 36.10 b) 44.50 22. A transparent solid cylindrical rod has a refractive
0
c) 26.8 d) 28.90
14. A light beam is incident at an angle twice the 2
index of . It is surrounded by air. A light ray
angle of refraction. The angle of refraction is 3
is incident at the mid-point of one end of the rod
1   
a) 2 cos   b) cos–1(2µ) as shown in the figure
2
1   
c) cos 1   d) cos
1
2 2 2 The incident angle  for which the light ray grazes
along the wall of the rod is

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Refraction of Light 17

a) sin–1(1/2) b) sin 1 ( 3 / 2) 8.5 Optical fibre

26. Consider telecommunication through optical
c) sin 1 (2 / 3 ) d) sin 1 (1 / 3 ) fibres. Which of the following statements is not
true ?
a) Optical fibre may have homogeneous core
8.4 Critical angle
with a suitable cladding.
23. White light is incident on the interface of glass
b) Optical fibres can be of graded refractive
and air is shown in the figure. If green light is just
index
totally internally reflected then the emerging ray
c) Optical fibres are subject to electromagnetic
in air contains
interference from outside
d) Optical fibres have extremely low transmission
loss
Air Green 27. Assertion : In optical fibre, the diameter of the
Glass core is kept small.
Reason : This smaller diameter of the core
White ensures that the fibre should have incident angle
more than the critical angle required for total
a) yellow, orange and red internal reflection.
b) violet, indigo and blue a) Assertion is True, Reason is True; Reason is
c) all colours a correct explanation for Assertion.
d) all colours except green b) Assertion is True, Reason is True; Reason is
24. A green light is incident from the water to the not a correct explanation for Assertion
air-water interface at the critical angle (). Select c) Assertion is True, Reason is False
the correct statement d) Assertion is False, Reason is True
a) The entire spectrum of visible light will come
out of the water at an angle of 900 to the normal 8.6 Dispersion of light
b) The spectrum of visible light whose frequency 28. Assertion : There is no dispersion of light
is less than that of green light will come out to refracted through a rectangular glass slab.
the air medium Reason : Dispersion of light is the pheonomenon
c) The spectrum of visible light whose frequency of splitting of a beam of white light into its
is more than that of green light will come out constituent colours.
to the air medium a) Assertion is True, Reason is True; Reason is
d) The entire spectrum of visible light will come a correct explanation for Assertion.
out of the water at various angles to the normal b) Assertion is True, Reason is True; Reason is
not a correct explanation for Assertion
25. A light beam is travelling from Region I to Region
c) Assertion is True, Reason is False
IV (Refer Figure). The refractive index in Region
d) Assertion is False, Reason is True
n0 n0 n0 29. A prism (µ = 1.5) has the refracting angle of 300.
I, II, III and IV are n 0, , and ,
2 6 8 The deviation of a monochromatic ray incident
respectively. The angle of incidence  for which normally on its one surface will be
the beam just misses entering Region IV is [sin 480 36' = 0.75]
a) 180 36' b) 200 30'
Region I Region II Region III Region IV c) 18 0
d) 220 1'
 n0 n0 n0
2
8.7 Prism and prism formula
n0 6 8
30. If the angle of prism is 600 and the angle of
 0.2m 0.6m
minimum deviation is 400, the angle of refraction
will be
a) 300 b) 600
1  3  1  1 
a) sin   b) sin  
0
c) 100 d) 1200
 4 8 31. In the position of minimum deviation when a ray
of yellow light passes through the prism, then its
1  1  1  1 
c) sin   d) sin   angle of incidence is
4  3 a) less than the emergent angle
b) greater than the emergent angle

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Refraction of Light 18
c) sum of angle of incidence and emergent angle The angle of minimum deviation will be
is 900 a) less than 410 b) equal to 410
d) equal to the emergent angle c) more than 41 0
d) zero
32. The graph between angle of deviation () and 38. A ray of monochromatic light suffers minimum
angle of incidence (i) for a triangular prism is deviation of 380 while passing through a prism of
represented by refracting angle 600. Refractive index of the prism
material is
a) 1.5 b) 1.3
  c) 0.8 d) 2.4
39. A prism of a refracting angle 600 is made with a
a) b)
material of refractive index µ. For a certain
O i O i wavelength of light, the angle of minimum
deviation is 300. For this wavelength, the value of
µ of material is
a) 1.820 b) 1.503
  c) 1.414 d) 1.231
c) d) 40. The angle of minimum deviation for an incident
light ray on an equilateral prism is equal to its
O i O i refracting angle. The refractive index of its
material is
33. A ray of light is incident on an equilateral glass
prism placed on a horizontal table. For minimum 1
deviation which ofthe following is true ? a) b) 3
2

R 3 3
Q c) d)
2 2
S
P 41. The refractive index of a prism for a
monochromatic wave is 2 and its refracting
a) PQ is horizontal
angle is 600. For minimum deviation, the angle of
b) QR is horizontal
incidence will be
c) RS is horizontal
a) 300 b) 450
d) Either PQ or RS is horizontal 0
c) 60 d) 750
34. The angle of minimum deviation for a prism is
42. For an angle of incidence  on an equilateral prism
400 and the angle of the prism is 600. The angle
of incidence in this position will be of refractive index 3 , the ray refracted is
a) 300 b) 600 parallel to the base inside the prism. The value of
 is
0
c) 50 d) 1000
35. Two beams of red and violet colours are made to a) 300 b) 450
pass separately through a prism of A = 600. In c) 60 0
d) 750
the minimum deviation position, the angle of 43. The refractive index of the material of an
refraction inside the prism will be equilateral prism is 1.6. The angle of minimum
a) greater for red colour deviation due to the prism would be
b) equal but not 300 for both the colours a) 300
c) greater for violet colour b) between 300 and 450
d) 300 for both the colours c) 450
36. A ray of light passes through an equilateral glass
d) between 300 and 600
prism in such a manner that the angle of incidence
is equal to the angle of emergence and each of
8.8 Angular dispersion and dispersive power
these angles is equal to 3/4 of the angle of the
44. The refractive indices for the light of violet and
prism. The angle of deviation is
red colours of any material are 1.66 and 1.64
a) 450 b) 390
0 respectively. If the angle of prism made of this
c) 20 d) 300
material is 100, then angular dispersion will be
37. A parallel beam of monochromatic light is incident
on one surface of an equiliteral prism. Angle of a) 0.200 b) 0.100
0
incidence is 550 and angle of emergence is 460. c) 0.40 d) 1 0

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Refraction of Light 19
45. A spectrum is formed by a prism of dispersive 8.10 Scattering of light
power . If the angle of deviation is , then the 53. Blue colour of sea water is due to
angular dispersion is a) image of sky in water
  b) refraction of sunlight
a) b) c) interference of sunlight reflected from the
  water surface
1 d) scattering of sunlight by the water molecules
c) d)  54. Assertion : A red object appears dark in yellow

46. A thin prism P of refracting angle 30 and refractive light.
index 1.5 is combined with another thin prism Q Reason : Red colour is scattered less.
of refractive index 1.6 to produce dispersion a) Assertion is True, Reason is True; Reason is
without deviation. Then the angle of prism Q is a correct explanation for Assertion.
a) 3 0 b) 4 0 b) Assertion is True, Reason is True; Reason is
c) 3.5 0
d) 2.50 not a correct explanation for Assertion
47. An achromatic prism is made by combining two c) Assertion is True, Reason is False
prisms P1(µv = 1.523, µ = 1.515) and d) Assertion is False, Reason is True
P2(µv = 1.616, µ = 1.650); where µ represents
the refractive index. If the angle of the prism P 1 8.11 Blue colour of the sky
is 100, then the angle of the prism P2 will be 55. The reason for blue colour of sky in the afternoon
a) 5 0 b) 7.80 is
c) 10.6 0
d) 200 a) interference b) refraction
48. Dispersive power depends upon c) polarization d) scattering
a) the shape of prism b) material of prism 56. What will be the colour of the sky as seen from
c) angle of prism d) height of the prism the earth if there were no atmosphere ?
49. In the visible region the dispersive powers and a) Black b) Blue
the mean angular deviations for crown and flint c) Orange d) Red
glass prisms are , ' and d, d' respectively. The
condition for getting deviation without dispersion 8.12 Colour of the sun at sunrise and sunset
when the two prisms are combined is 57. At sunrise or sunset, the sun looks more red than
at mid-day because
a) d  ' d'  0 b) 'd + d' = 0 a) the sun is hottest at these times
c) d + 'd' = 0 d) (d)2 + ('d')2 = 0 b) of the scattering of light
8.9 Rainbow c) of the effects of refraction
50. In the formation of a rainbow, light from the sun d) of the effects of diffraction
on water droplets undergoes
a) dispersion only Miscellaneous
b) only total internal reflection 58. Check the correct statements on scattering of
c) dispersion and total internal reflection light.
d) none of these S1: Rayleigh scattering is responsible for the
51. In the formation of primary rainbow, the sunlight bluish appearance of day.
rays emerge at minimum deviation from rain-drop S2: Rayleigh scattering is proportional ot 1/4
after when the size of the scatterer is much less
a) one internal reflection and one refraction than .t
b) one internal reflection and two refraction S3: Clouds having droplets of water (large
c) two internal reflections and one refraction scattering objects) scatter all wavelengths
d) two internal reflections and two refractions almost equal and so are generally white
52. Pick the correct statement from the following S4: The sun looks reddish at sunset and sunrise
a) Primary rainbow is a virtual image and due to Rayleigh scattering
secondary rainbow is a real image a) S1 only b) S1 and S2
b) Primary rainbow is a real image and secondary c) S2 and S3 d) S1, S2, S3 and S4
rainbow is a virtual image 59. If the critical angle for total internal reflection
c) Both primary and secondary rainbows are from a medium to vacuum is 300, the velocity of
virtual images light in the medium is
d) Both primary and secondary rainbows are real a) 3 × 108 m/s b) 1.5 × 108 m/s
images
c) 6 × 108 m/s d) 3  108 m/s

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Refraction of Light 20
60. Which of the following is not a correct statement? 1
a) The wavelength of red light is greater than c) s d) 2 s
the wavelength of green light
2
b) The wavelength of blue light is smaller than 66. A light wave enters from air into a medium of
the wavelength of orange light 4
c) The frequency of green light is greater than refractive index . If wavelength of light in air
3
the frequency of blue light is 6000 Å, then the wave number of light in
d) The frequency of violet light is greater than medium is
the frequency of blue light a) 1.1 × 106 b) 4.4 × 106
61. A light passes through glass slab of refractive c) 2.2 × 10 6
d) 6 × 106
index 1.5 and thickness 2 mm. How much time 67. Time taken by the light to travel through 5 cm of
ray will take to pass through the glass slab ? glass is same as that through x cm of air. If R.I.
a) 10–16 s b) 10–11 s of glass is 1.5, then x is
–8
c) 10 s d) 10–17 s a) 7.5 cm b) 1.33 cm
62. Each quarter of a vessel of depth H is filled with c) 9 cm d) 6 cm
liquids of the refractive indices n1, n2, n3 and n4 68. Assertion : By roughening the surface of a glass
from the bottom respectively. The apparent depth sheet its transparency can be reduced.
of the vessel when looked normally is Reason : Glass sheet with rough surface absorbs
H ( n1  n 2  n 3  n 4 ) more light.
a) a) Assertion is True, Reason is True; Reason is
4
a correct explanation for Assertion.
 1 1 1 1  b) Assertion is True, Reason is True; Reason is
H    
not a correct explanation for Assertion
b)  n 1 n 2 n 3 n 4 
c) Assertion is True, Reason is False
4
d) Assertion is False, Reason is True
(n1  n 2  n 3  n 4 )
c)
4H Raman effect
 1 1 1 1 
H    
d)  n 1 n 2 n 3 n 4 
2
63. How much water should be filled in a container
21 cm in height, so that it appears half filled when
viewed from the top of the container ?
4
[Given that : a  w  ]
3
a) 8.0 cm b) 10.5 cm
c) 12.0 cm d) 14.0 cm
The scattering of light by molecules or crystal
64. The angle of a prism is A. One of its refracting
lattices is a weak effect. When monochromatic
surfaces is silvered. Light rays falling at an angle light is scattered by molecules or crystal lattice,
of incidence 2A on the first surface returns back spectral analysis shows an intense spectral line
through the same path after suffering reflection matching the wavelength of the light source.
at the silvered surface. The refractive index µ, of These lines are called Raman lines (after the
the prism is Indian physicist C.V.Raman). Although these
a) 2 sin A b) 2 cos A lines already been predicted theoretically,
Raman was the first who experimentally
1 confirmed them in 1928.
c) cos A d) tan A
2
65. Light passes through glass of refractive index 1.5.
What is the time required for light to travel
4 × 108 m in glass ?
1
a) 4 s b) s
4

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