Class 12 Physics Chapter 10 Unit 6 • Optics part 2 • Wave optics • 10 Assertion and Reason Type questions • Solution with explanation
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CATCH THROUGH
WORDS
Class 12 Physics
Chapter 10
Unit 6
• Optics part 2
• Wave optics
• 10 Assertion and Reason
Type questions
• Directions. In the following questions, statement
of assertion is followed by a statement of
reason. While answering a question, you are
required to choose the correct one out of the
given four responses and mark it as :-
• A, if both assertion and reason are true and
reason is the correct explanation of the
assertion.
• B, if both assertion and reason are true but
reason is not correct explanation of the
assertion.
• C, if assertion is true, but reason is false.
• D, if both assertion and reason are false.
1) Assertion : Corpuscular theory fails in
explaining the velocities of light in air and
water.
Reason : According to corpuscular
theory, light should travel faster in denser
media than in rarer media.
1) A. 2) B
3) C. 4) D
2) Assertion : In young’s double slit
experiment, the fringe width for dark fringes
is different from that for white fringes.
Reason : In young’s double slit
experiment performed with a source of
white light, only black and bright fringes are
observed.
1. A. 2. B
3. C. 4. D
3)Assertion : No interference pattern
is observed, when two coherent sources
are infinitely close to each other.
Reason : The fringe width is inversely
proportional to the distance between
the two slits.
1) A. 2) B
3) C. 4) D
4) Assertion : In young’s double slit
experiment, the fringe width for dark
fringes is equal to that for white fringes .
Reason : In young’s double slit
experiment performed with a source of
white light, only black and white fringes
are observed.
1) A. 2) B
3) C. 4) D
5) Assertion : In young’s double slit
experiment, the two slits are at distance d apart.
Interference pattern is observed on the screen.
When it is directly opposite to one of the slits, a
dark fringe is observed. Then, the wavelength of
the wave is proportional to the square of the
distance of the slits.
Reason : For a dark fringe, the intensity is
zero.
1) A 2) B
3) C 4) D
6) Assertion : Coloured spectrum is seen,
when we look through a muslin cloth.
Reason : It is due to the diffraction of white
light on passing through fine slits.
1) A. 2) B
3) C. 4) D
7) Assertion : When a tiny circular
obstacle is placed in the path of light from
some distance, a bright spot is seen at the
centre of the shadow of the obstacle.
Reason : Destructive interference
occurs at the centre of the shadow.
1) A. 2) B
3) C. 4) D
8) Assertion: When a light wave travels
from a rarer to a denser medium, it loses
speed.The reduction in speed imply a
reduction in energy carried by the light
wave.
Reason : The energy of a wave is
proportional to velocity of wave.
1) A. 2) B
3) C. 4) D
9) Assertion : For best contrast between
maxima and minima in the interference
pattern of Young’s double slit experiment,
the intensity of emerging out of the two slits
should be equal.
Reason : The intensity of interference
pattern is proportional to square of
amplitude.
1) A. 2) B
3) C. 4) D
10) Assertion : Interference pattern
is made by using blue light instead of
red light, the fringes becomes narrower
Reason: In Young’s double slit
experiment, fringe width is given by
relation B = Lambda D/d
1) A
2) B
3) C
4) D
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11) Assertion : The rainbow is seen
something in the sky, when it is raining.
When one sees a rainbow, one’s back is
towards the sun.
Reason : Internal reflection from water
droplet causes dispersion. The final ray is
in the backward direction.
1) A 2) B
3) C 4) D
12) Assertion : The air bubble shines
in water.
Reason : It is because of refraction of
light.
1) A. 2) B
3) C. 4) D
13) Assertion : A double convex lens
(n=1.5) has focal length 10cm. When the
lens is immersed in water(n=4/3) its
focal length becomes 40cm.
Reason: Because,
1/f = ( n2/n1 - 1) ( 1/R1 - 1/R2)
1) A. 2) B
3) C. 4) D
14) Assertion : Critical angle of light
passing from glass to air is minimum for
violet colour.
Reason : The wavelength of blue light is
greater than the light of other colours
1) A
2) B
3) C
4) D
15) Assertion : The images formed by
total internal reflections are much brighter
than those formed by mirror or lenses.
Reason : There is no loss of intensity in
total internal reflection.
1) A
2) B
3) C
4) D
16) Assertion : The focal length of
lens does not change when red light is
replaced by blue light.
Reason: The focal length of lens does
not depends on colour of light used.
1) A
2) B
3) C
4) D
17) Assertion : By increasing the
diameter of the objective of telescope,
we can increase its range.
Reason: The range of a telescope tells
us how far away a star of some standard
brightness can be spotted by telescope.
1) A
2) B
3) C
4) D
18) Assertion: If objective and eye
lenses of a microscope are
interchanged then it can work as
telescope.
Reason: The objective of telescope
has small focal length.
1) A
2) B
3) C
4) D
19) Assertion : If the angles of the base of
the prism are equal, then in the position of
minimum deviation,the refracted ray will pass
parallel to the base of prism.
Reasons : In the case of minimum
deviation,the angle of incidence is equal to
the angle if emergence.
1) A. 2) B
3) C. 4) D
20) Assertion : The refractive index of
a prism depends only on the kind of glass
of which it is made of and the colour of
light.
Reason : The refractive index of a
prism does not depend on wavelength of
light.
1) A. 2) B
3) C. 4) D
SEE ANSWERS HERE WITH EXPLAINED
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