Download INDIAN SCHOOL DARSAIT

INDIAN SCHOOL DARSAIT
DEPARTMENT OF SCIENCE
CLASS X -PHYSICS (TERM 2)
CBSE BOARD PAPERS WITH SOLUTION
ISD/X/PHY/SA/2016
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1.
AB and CD, two spherical mirrors, form parts of a hollow spherical ball with its
centre at O as shown in the diagram. If arc AB =1/2 arc CD, what is the ratio of their
focal lengths? State which of the two mirrors will always form virtual image of an
object placed in front of it and why?
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Focal length of both the mirrors will be the same / 1: 1
Mirror AB will always form virtual image as it is a diverging / convex mirror
2.
“The magnification produced by a spherical mirror is -3.” List four informations you obtain
from this statement about the mirror/image.
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1)Inverted image; 2) magnified; 3) concave mirror ; 4) real image
3.
Name the type of mirrors used in the design of solar furnaces. Explain how high
temperature is achieved by this device.
 Concave Mirrors / Converging Mirrors
 When a solar furnace is placed at the focus of a large concave mirror/
reflector, it focuses a parallel beam of light on the furnace; consequently a
high temperature is achieved after some time.
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4.
State two positions in which a concave mirror produces a magnified image of a
given object. List two differences between the two images.
When the object is placed in front of the mirror –
(i) between its pole and focus
(ii) between the focus and centre of curvature
In case (i) the image is virtual and erect
In case (ii) the image is real and inverted
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5.
List four characteristics of the images formed by plane mirrors.
(i) Virtual ii) Erect iii) Same size as the object iv) As far behind the mirror as the object is
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in front v) Laterally inverted
6.
The refractive indices of glass and water with respect to air are3/2 and 4/3
respectively. If speed of light in glass is 2x108m/s, find the speed of light in water.
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7.
The image of an object formed by a mirror is real, inverted and is of magnification
-1. If the image is at a distance of 40cm from the mirror, where is the object
placed? Where would the image be if the object is moved 20cm towards the
mirror? State the reason and also draw ray diagram for the new position of the
object to justify your answer?
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Object position: At C ( Centre of curvature)
Object distance = 40 cm
Position of the image - at infinity
Reason – Focal length of the mirror = 20 cm
If the object is moved 20 cm towards the mirror then its new position would be at the
focus of the mirror.
8.
To construct a ray diagram we use two rays of light which are so chosen that it is
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easy to determine their directions after reflection from the mirror. Choose these
two rays and state the path of these rays after reflection from a concave mirror.
Use these two rays to find the nature and position of the image of an object placed
at a distance of 15cm from a concave mirror of focal length 10cm.
i)
A ray parallel to the principal axis, after reflection, will pass through the
principal focus of a concave mirror.
ii)
A ray passing through the principal focus of a concave mirror after
reflection will emerge parallel to the principal axis.
iii)
A ray passing through the centre of curvature of a concave mirror after
reflection is reflected back along the same path.
iv)
A ray incident obliquely to the principal axis towards the pole of a concave
mirror is reflected obliquely, making equal angles with the principal axis.
(any two)
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9.
Draw the following diagram, in which a ray of light is incident on a concave/convex
mirror, on your answer sheet. Show the path of this ray, after reflection, in each
case.
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10. If the image formed by a mirror for all positions of the object placed in front of it is
always erect and diminished, what type of mirror is it? Draw a ray diagram to
justify your answer. Where and why do we generally use this type of mirror?
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Convex mirror
Use: As rear view mirror in vehicles/ Also in Malls, Hotels, and Airports for
security reasons.
It Forms erect image and gives Wider field of view.
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11. (a) Define focal length of a spherical lens.
(b) A divergent lens has a focal length of 30cm. At what distance should an object
of height 5cm from the optical centre of the lens be placed so that its image is
formed 15cm away from the lens? Find the size of the image also.
(c) Draw a ray diagram to show the formation of image in the above situation.
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12. If the image formed by a lens for all positions of the object placed in front of it is
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always virtual, erect and diminished, state the type of the lens. Draw a ray diagram
in support of your answer. If the numerical value of focal length of such a lens is 20
cm, find its power in new Cartesian sign conventions.
13. The image of an object formed by a lens is of magnification-1. If the distance
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between the object and its image is 60cm, what is the focal length of the lens? If
the object is moved 20cm towards the lens, where would the image be formed?
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State reason and also draw a ray diagram in support of your answer.
Image with magnification -1 means image is inverted and of the same size.
Therefore, object is at 2F and the image is also at 2F on the other side of the lens.
Therefore, distance between the object and its image is 4f = 60 cm
f = 15 cm
Object distance 2f = 30 cm. if the object is shifted towards the lens by 20 cm, the
new object distance = 30 cm – 20 cm = 10 cm. This distance is less than the focal
length, and the image formed in this case would be virtual, erect and will form on
the same side as the object.
14. Describe an activity to show that the colours of white light splitted by a glass prism
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can be recombined to get white light by another identical glass prism. Also draw
ray diagram to show the recombination of the spectrum of white light.
Description of activity- When a glass prism is used to obtain a spectrum of
sunlight, a second identical prism in an inverted position with respect to the first
position will allow all the colours of spectrum to recombine .Thus a beam of
white light will emerge from the other side of the second prism.
15. Explain in brief the reason for each of the following :
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(a) Advanced sun-rise
(b) Delayed sun-set
(c) Twinkling of stars
Advanced sunrise − When the sun is slightly below the horizon light rays coming
from the sun travel from the rarer to denser medium layers of air because of
atmospheric refraction of light, light appears to come from a higher position
above the horizon. Thus the sun appear earlier than actual sun rise
Delayed sun set − Same reason as similar refraction occurs at the sunset
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Twinkling of stars – the light coming from the stars gets refracted several times
before reaching the observers eye. Due to change in physical condition of the
atmosphere the light sometimes reaches the observer and sometimes it doesn’t,
hence they appear to twinkle.
16. Why does the sun appear reddish early in the morning? Will this phenomenon be
observed by an observer on the moon? Justify your answer with a reason.
Early in the morning, the sun is near the horizon, sunlight reaches us after
travelling a longer distance through thick layers of atmosphere. Thus most of the
blue light and shorter wavelengths are scattered away by the particles in the
atmosphere. The light that reaches us is of longer wavelengths giving a reddish
appearance.
This phenomenon will not be observed by an observer on the moon. Because of
the absence of atmosphere on the moon.
17. (a) Define the following terms in the context of spherical mirrors :
(i) Pole
(ii) Centre of curvature
(iii) Principal axis
(iv) Principal focus
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(b) Draw ray diagrams to show the principal focus of a :
(i) Concave mirror
(ii) Convex mirror
(c) Consider the following diagram in which M is a mirror and P is an object and Q is
its magnified image formed by the mirror. State the type of the mirror M and one
characteristic property of the image Q.
a) i) Pole – Centre of the reflecting surface of the mirror.
ii) Centre of curvature – The centre of the hollow sphere of which the reflecting
surface of mirror forms a part.
iii) Principal axis – Straight-line passing through the pole and the centre of
curvature of a spherical mirror.
iv) Principal focus – Incident rays parallel to principal axis, after reflection, either
converge to or appear to diverge from a fixed point on the principal axis called
principal focus of the spherical mirror
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c) Concave mirror. Image formed is virtual
18. Suppose you have three concave mirrors A, B and C of focal lengths 10 cm, 15 cm
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and 20 cm. For each concave mirror you perform the experiment of image
formation for three values of object distance of 10 cm, 20 cm and 30 cm. Giving
reason answer the following :
(a) For the three object distances, identify the mirror/mirrors which will form an
image of magnification – 1.
(b) Out of the three mirrors identify the mirror which would be preferred to be
used for shaving purposes/makeup.
(c) For the mirror B draw ray diagram for image formation for object distances 10
cm and 20 cm.
19. It is desired to obtain an erect image of an object, using concave mirror of focal
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length of 12cm.
(i)
What should be the range of distance of an object in front of the mirror?
(ii)
Will the image be smaller or larger than the object? Draw ray diagram to
show the formation of image in this case.
(iii)
Where will the image of this object be, if it is placed 24cm in front of the
mirror? Draw ray diagram for this situation also to justify your answer.
Show the positions of pole, principal focus and the centre of curvature in
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the above ray diagrams.
(i) Range of distance – between 0 cm - < 12 cm
ii) larger than the object
iii) Image also at 24 cm in front of the mirror
20.
(a) State the laws of refraction of light. Explain the term absolute refractive
index of a medium and write an expression to relate it with speed of light in
vacuum.
(b) The absolute refractive indices of two media ‘A’ and ‘B’ are 2 and 1.5
respectively. If the speed of light in medium ‘B is 2x108m/s, calculate the
speed of light in :
(i)
Vacuum
(ii)
Medium A
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(a) Laws of refractionThe incident ray, the refracted ray and the normal to the interface of two
transparent media at the point of incidence, all lie in the same plane.
Snell’s law- The ratio of sine of angle of incidence to the sine of angle of
refraction is a constant, for the light of a given color and for the given pair of
media.
Absolute refractive indexIt is the ratio of speed of light in vacuum to the speed of light in medium is called
Refractive index. n=c/v
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21. “ A convex lens can form a magnified, erect as well as magnified inverted image of
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an object placed in front of it.” Draw ray diagram to justify this statement stating
the position of the object with respect to the lens in each case.
An object of height 4cm is placed at a distance of 20cm from a concave lens of focal
length 10cm. Use lens formula to determine the position of the image formed.
For magnified erect image – Object is between the optical centre and principal
focus of a convex lens
For magnified inverted image – object between F and 2F of a convex lens
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22.
(a) Define optic centre of a spherical lens.
(b) A divergent lens has a focal length of 20cm. At what distance should an
object of height 4cm from the optic centre of the lens be placed so that its
image is formed 10cm away from the lens. Find the size of the image also.
(c) Draw a ray diagram to show the formation of image in above situation.
23. What is meant by power of a lens? Define its SI unit
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You have two lenses A and B of focal lengths +10cm and -10cm respectively. State
the nature and power of each lens. Which of the two lenses will form a virtual
magnified image of an object placed 8cm from the lens? Draw a ray diagram to
justify your answer.
Power of lens:- Ability of a lens to converge or diverge the light rays falling on it/
The degree of convergence or divergence of light rays achieved by a lens/
Reciprocal of focal length of the lens.
1 dioptre – It is the power of a lens whose focal length is 1 metre.
A-Converging/ Convex lens and power=+10D
B - Diverging/ Concave lens and power=-10D
In this case the object will be between the optical centre and principal focus of
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the lens. Hence the convex lens, i.e., lens A will form virtual and magnified image
of the object.
24. (a) Draw a ray diagram to show the formation of image by a convex lens when an
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object is placed in front of the lens between its optical centre and principal focus.
(b) In the above ray diagram mark the object-distance (u) and the image-distance
(v) with their proper signs (+ve or – ve as per the new Cartesian sign convention)
and state how these distances are related to the focal length (f) of the convex lens
in this case.
(c) Find the power of a convex lens which forms a real, and inverted image of
magnification –1 of an object placed at a distance of 20 cm from its optical centre
25. At what distance from a concave lens of focal length 20 cm a 6 cm tall object be
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placed so as to obtain its image at 15 cm from the lens? Also calculate the size of
the image formed.
Draw a ray diagram to justify your answer for the above situation and label it.
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26. One half of a convex lens of focal length 10cm is covered with a black paper. Can
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such a lens produce an image of a complete object placed at a distance of 30cm
from the lens? Draw a ray diagram to justify your answer.
A 4cm tall object is placed perpendicular to the principal axis of a convex lens of
focal length 20cm. The distance of the object from the lens is 15cm. Find the
nature, position and size of the image.
Yes
27. A student is unable to see clearly the words written on the blackboard placed at a
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distance of approximately 4m from him. Name the defect of vision the boy is
suffering from. Explain the method of correcting this defect. Draw ray diagram for
the:
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(i)
(ii)
Defect of vision and also
For its correction.
Defect – Myopia / Nearsightedness
Correction – By using a concave lens of suitable power
28. (a) Write the function of each of the following parts of human eye :
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Cornea; iris; crystalline lens; ciliary muscles
(b) Millions of people of the developing countries of world are suffering from
corneal blindness. These persons can be cured by replacing the defective cornea
with the cornea of a donated eye. A charitable society of your city has organized a
campaign in your neighborhood in order to create awareness about this fact. If you
are asked to participate in this mission how would you contribute in this noble
cause?
(i) State the objective of organizing such campaigns.
(ii) List two arguments which you would give to motivate the people to donate
their eyes after death.
(iii) List two values which are developed in the persons who actively participate and
contribute in such programmes.
a) Cornea – Refracts the rays of light falling on the eye
Iris – Controls the size of the pupil
Crystalline lens – Focuses the image of the object on the retina
Ciliary muscles – Holds the eye lens and adjusts its focal length
b) i) Objectives – To make people aware and realize their duties towards societ
ii) One person can give sight to two people. Our eyes can live even after our
death.
iii) Concern for others/ Responsible behavior/ Group work/ or any other.
29. Write the importance of ciliary muscles in the human eye. Name the defect of
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vision that arises due to gradual weakening of the ciliary muscles in old age. What
type of lenses is required by the persons suffering from this defect to see the
objects clearly?
Akshay, sitting in the last row in his class, could not see clearly the words written
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on the blackboard. When the teacher noticed it, he announced if any student
sitting in the front row could volunteer to exchange his seat with Akshay. Salman
immediately agreed to exchange his seat with Akshay. Akshay could now see the
words written on the blackboard clearly. The teacher thought it fit to send the
message to Akshay’s parents advising them to get his eye sight checked. In the
context of the above event, answer the following questions:
(a) Which defect of vision is Akshay suffering from? Which type of lens is used to
correct this defect?
(b) State the values displayed by the teacher and Salman.
(c) In your opinion, in what way can Akshay express his gratitude towards the
teacher and salman?
Ciliary muscles modify the curvature of the eye lens to enable the eye to focus
objects at varying distances/ help in adjusting the focal length of the eye lens.
defect- Presbyopia correction-Bifocal lens
(a) Defect – Myopia/ Nearsightedness
Corrective lens – Concave/ Diverging lens
(b) Values – Concerned, Caring etc. (one value of teacher, one value of Salman)
(c) By thanking the teacher and Salman
30. (a) What is dispersion of white light? State its cause.
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(b) “Rainbow is an example of dispersion of sunlight.” Justify this statement by
explaining, with the help of a labeled diagram, the formation of a rainbow in the
sky. List two essential conditions for observing a rainbow.
a) Definition of Dispersion: Splitting of white light into seven constituent colors
by a prism.
Cause of dispersion − when white light passes through a glass prism, different
constituent colors bend through different angles with respect to the incident ray
and hence are separated.
b)
Conditions for observing a rainbow − i) after the rainfall/ at a water fountain
ii) sun is at the back of the observer
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Section B
31. A student determines the focal length of a device ‘X’ by focusing the image of a
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distant object on a screen placed 20 cm from the device on the same side as the
object.
The device ‘X’ is
(a) Concave lens of focal length 10 cm
(b) Convex lens of focal length 20 cm
(c) Concave mirror of focal length 10 cm
(d) Concave mirror of focal length 20 cm
32. Study the following diagram and select the correct statement about the device ‘X’:
(a)
(b)
(c)
(d)
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Device X is a concave mirror of radius of curvature 12cm
Device X is a concave mirror of focal length 6cm
Device X is a concave mirror of focal length 12cm
Device X is a convex mirror of focal length 6cm
33. To determine the approximate value of the focal length of a given concave mirror,
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you focus the image of a distant object formed by the mirror on a screen. The
image obtained on the screen, as compared to the object is always:
(a) Laterally inverted and diminished
(b) Inverted and diminished
(c) Erect and diminished
(d) Erect and highly diminished
34. A student has obtained a point image of a distant object using the given convex
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lens. To find the focal length of the lens he should measure the distance between
the:
(a) Lens and the object only
(b) Lens and the screen only
(c) Object and image only
(d) Lens and the object and also between the object and the image
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35. A student obtains a sharp image of the distant window (W) of the school laboratory
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on the screen (S) using the given concave mirror (M) to determine its focal length.
Which of the following distances should he measure to get the focal length of the
mirror?
(a)
(b)
(c)
(d)
MW
MS
SW
MW-MS
36. A teacher sets up the stand carrying a convex lens of focal length 15 cm at 42.7 cm
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mark on the optical bench. He asks four students A, B, C and D to suggest the
position of screen on the optical bench so that a distinct image of a distant tree is
obtained almost immediately on it. The positions suggested by the students were
as :
A. 12.7 cm
B. 29.7 cm
C. 57.7 cm
D. 72.7 cm
The correct position of the screen was suggested by
(a) A
(b) B
(c) C
(d) D
37. Suppose you have focused on a screen the image of candle flame placed at the
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farthest end of the laboratory table using a convex lens. If your teacher suggests
you to focus the parallel rays of sun, reaching your laboratory table, on the same
screen, what you are expected to do is to move the:
(a) Lens slightly towards the screen
(b) Lens slightly away from the screen
(c) Lens slightly towards the sun
(d) Lens and screen both towards the sun
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38. A student obtained a sharp image of a candle flame placed at the distant end of the
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laboratory table on a screen using a concave mirror to determine its focal length.
The teacher suggested him to focus a distant building about 1 km far from the
laboratory, for getting more correct value of the focal length. In order to focus the
distant building on the same screen the student should slightly move the :
(a) mirror away from the screen
(b) screen away from the mirror
(c) screen towards the mirror
(d) screen towards the building
39. To determine the approximate focal length of the given convex lens by focusing a
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distant object (say, a sign board), you try to focus the image of the object on a
screen. The image you obtain on the screen is always :
(a) erect and laterally inverted
(b) erect and diminished
(c) inverted and diminished
(d) virtual, inverted and diminished
40. Select from the following the best experimental set-up for tracing the path of a ray
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of light passing through a rectangular glass slab :
(a) P
(b) Q
(c) R
(d) S
41. A student has traced the path of a ray of light through a glass slab as follows. If you
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are asked to label 1, 2, 3 and 4, the correct sequencing of labeling i, e, r and lateral
displacement respectively is
(a) 2, 1, 3, 4
(b) 1, 2, 3, 4
(c) 1, 3, 2, 4
(d) 1, 3, 4, 2
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42. A student traces the path of a ray of light through a rectangular glass slab for the
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different values of angle of incidence. He observes all possible precautions at each
step of the experiment. At the end of the experiment, on analyzing the
measurements, which of the following conclusions is he likely to draw?
(a) i=e<r
(b) i<e<r
(c) i>e>r
(d) i=e>r
43. In your laboratory you trace the path of light rays through a glass slab for different
1
values of angle of incidence and in each case measure the values of the
corresponding angle of refraction and angle of emergence. On the basis of your
observations your correct conclusion is:
(a) ‘i’ is more than ‘r’, but nearly equal to ‘e’
(b) ‘i’ is less than ‘r’, but nearly equal to ‘e’
(c) ‘i’ is more than ‘e’, but nearly equal to ‘r’
(d) ‘i’ is less than ‘e’, but nearly equal to ‘r’
44. Four students P, Q, R and S traced the path of a ray of light passing through a glass
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400
slab for an angle of incidence
and measured the angle of refraction. The values
0
as measured by them were 18 ; 220; 250 and 300 respectively. The student who has
performed the experiment methodically is
(a) P
(b) Q
(c) R
(d) S
45. A student traces the path of a ray of light through a triangular prism for different
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values of angle of incidence. On analyzing the ray diagrams, which one of the
following conclusions is he likely to draw?
(a)
(b)
(c)
(d)
The emergent ray is parallel to the incident ray.
The emergent ray bends at an angle to the direction of incident ray.
The emergent ray and the refracted ray are at right angles to each other.
The emergent ray is perpendicular to the incident ray.
46. In an experiment to trace the path of a ray of light through a triangular glass prism,
a student would observe that the emergent ray
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(a) is parallel to the incident ray.
(b) is along the same direction of incident ray.
(c) gets deviated and bends towards the thinner part of the prism.
(d) gets deviated and bends towards the thicker part (base) of the prism.
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47. Study the following figure in which a student has marked the angle of incidence (i),
angle of refraction (r), angle of emergence (e), angle of prism (A) and the angle of
deviation (D). The correctly marked angles are :
(a) ∠A and ∠i
(b) ∠A, ∠i and ∠r
(c) ∠A, ∠i, ∠e and ∠D
(d) ∠A, ∠i, ∠r and ∠D
48. To find the image distance for varying object distances in case of a convex lens of
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focal length 15 cm, a student obtains on a screen a sharp image of a bright object
by placing it at 20 cm distance from the lens. After that he gradually moves the
object away from the lens and each time focuses the image on the screen.
(a) In which direction-towards or away from the lens does he move the screen to
focus the object?
(b) How does the size of image change?
(c) Approximately at what distance does he obtain the image of magnification –1?
(d) How does the intensity of image change as the object moves farther and farther
away from the lens?
a) Towards the lens
b) Size decreases gradually
c) Nearly 30 cm from the lens
d) Intensity of the image gradually increases
49. A student focuses the image of a well illuminated distant object on a screen using a
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convex lens. After that he gradually moves the object towards the lens and each
time focuses its image on the screen by adjusting the lens.
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(i) In which direction-towards the screen or away from the screen, does he move
the lens?
(ii) What happens to the size of the image-does it decrease or increase?
(iii) What happens to the image on the screen when he moves the object very close
to the lens?
(i) Lens towards the screen/ screen away from the lens
(ii) Increase
(iii) No image on the screen
50. An object of height 2.5cm is placed at a distance of 15cm from the optical centre
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‘O’ of a convex lens of focal length 10cm. Draw a ray diagram to find the position
and size of the image formed. Mark optical centre ‘O’, principal focus F and height
of the image on the diagram.
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