Sure Shot Questions 2025

Chapter – 09
Ray Optics and Optical Instruments

➢ Questions 7. An object is placed 30 cm in front of a plano –

convex lens with its spherical surface of radius of
curvature 20 cm. If the refractive index of the
material of the lens is 1.5, find the position and
1. The radius of curvature of a convex mirror is 30 nature of the image formed.
cm. it forms an image of an object which is half the
size of the object. Find the separation between the 8. (a) Using the ray diagram for a system of two
object and the image. lenses of focal lengths f1 and f2 in contact with
each other, show that the two lens system can be
2. A convex lens (𝑛 = 1.52) has a focal length of regarded as equivalent to a single lens of focal
15.0 cm in air. Find its focal length when it is 1 1 1
immersed in liquid of refractive index 1.65. length f, where = + .
What will be the nature of the lens? f f1 f 2
Also write the relation for the equivalent power
3. An object is kept 20 cm in front of a concave mirror of the lens combination.
of radius of curvature 60 cm. Find the nature and (b) Determine the position of the image formed
position of the image formed. by the lens combination given in the figure.

4. An object is kept in front of a concave mirror of

focal length 15 cm. The image formed is real and
three times the size of the object. Calculate the
distance of the object from the mirror.
Three lenses of focal lengths +10 cm, -10 cm and
5. Two monochromatic rays of light are incident +30 cm are arranged coaxially as in the figure
normally on the face AB of an isosceles right- given below. Find the position of the final image
angled prism ABC. The refractive indices of the formed by the combination. [2/5, Delhi 2019]
glass prism for the two rays ‘1’ and ‘2’ are
respectively 1.35 and 1.45. Trace the path of these
rays after entering through the prism.

9. An astronomical telescope has an objective lens of

focal length 20 m and eyepiece of focal length 1
cm.
(a) Find the angular magnification of the
6. (a) Calculate the distance of an object of height h
telescope.
from a concave mirror of radius of curvature 20
(b) If the telescope is used to view the Moon, find
cm, so as to obtain a real image of magnification 2.
the diameter of the image formed by the
Find the location of image also,
objective lens. Given the diameter of the
(b) Using mirror formula, explain why does a
Moon is 3.5 x 106 m and radius of lunar orbit
convex mirror always produce a virtual image.
is 3.8 x 108 m.
[Delhi 2016]

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10. A ray of light falls on a transparent sphere with 16. A convex lens of focal length 20cm is placed
centre C as shown in the figure. The ray emerges coaxially with a convex mirror of radius of
from the sphere parallel to the line AB. Find the curvature 20 cm. The two are kept 15cm apart. A
angle of refraction at A if refractive index of the point object is placed 60 cm in front of the convex
material of the sphere is √3. lens. Draw a ray diagram to show the formation of
the image by the combination. Determine the
nature and the position of the image formed.

17. An object is placed in front of the convex lens

made of glass. How does the image distance vary
11. When a convex lens of focal length 30 cm is in if the refractive index of the medium is increased
contact with a concave lens of focal length 20 cm, in such a way that still it remains less than the
find out if the system is converging or diverging. glass?

12. A triangular prism of refracting angle 600 is made 18. (i) Define refractive index of a medium.
of a transparent material of refractive index 2/ (ii) In the following ray diagram, calculate the
√3. A ray of light is incident normally on the face speed of light in the liquid of unknown refractive
KL as shown in the figure. Trace the path of the index.
ray as it passes through the prism and calculate
the angle of emergence and angle of deviation.

19. Two monochromatic rays of light are incident

normally on the face AB of an isosceles right-
angled prism ABC. The refractive indices of the
glass prism for the two rays ‘1’ and ‘2’ are
13. Under what conditions does the phenomenon of respectively 1.35 and 1.45. Trace the path of these
total internal reflection take place? Draw a ray rays after entering through the prism.
diagram showing how a ray of light deviates by
900 after passing through a right-angled isosceles
prism.

14. A ray of light incident on the face AB of an

isosceles triangular prism makes an angle of
incidence (i) and deviates by angle 𝛽 as shown in
the figure. Show that in the position of minimum
deviation ∠𝛽 = ∠𝛼. Also find out the condition
when the refracted ray QR suffers total internal 20. (i) Draw a ray diagram to show the image
reflection. formation by a combination of two thin convex
lenses in contact. Obtain the expression for the
power of this combination in terms of the focal
lengths of the lenses.
(ii) A ray of light passing from air through an
equilateral glass prism undergoes minimum
3
deviation when the angle of incidence is 𝑡ℎ of
4
the angle of prism.

15. State, with the help of a ray diagram, the working 21. (i) A point of object is placed on the principal axis
principle of optical fibres. Write one important of the convex spherical surface of the radius of
use of optical fibres. curvature R, which separates the two media of
refractive indices n1 and n2 (n2 >n1). Draw the ray
diagram and deduce the relation between the

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 object distance (u), image distance (v) and the telescope. Deduce the expression for its
radius of curvature (R) for refraction to take place magnifying power when the final image is formed
at the convex spherical surface from rarer to at infinity.
denser medium.
(ii) A converging lens has a focal length of 20 cm in (ii) The sum of focal lengths of the two lenses of a
air. It is made of a material of refractive index 1.6. refractive telescope is 105 cm. The focal length of
If it is immersed in a liquid of refractive index 1.3, one lens is 20 times that of the other. Determine
find its new focal length. the total magnification of the telescope when the
final image is formed at infinity.
22.

27. (i) State the condition under which a large

magnification can be achieved in an astronomical
telescope.
(ii) Give two reasons to explain why a reflecting
telescope is preferred over a refracting telescope.

(i) Draw the ray diagram showing refraction of 28. Why should the objective of a telescope have
light through a glass prism and hence obtain the large focal length and large aperture? Justify your
relation between the refractive index 𝜇 of the answer.
prism , angle of prism and angle of minimum
deviation. 29. What is the difference in the construction of an
(ii) Determine the value of the angle of incidence astronomical telescope and a compound
for a ray of light travelling from a medium of microscope? The focal lengths of the objective
refractive index 𝜇1 = 2 into the medium of and eyepiece of a compound microscope are 1.25
refractive index 𝜇2 = 1, so that it just grazes along cm and 5.0 cm, respectively. Find the position of
the surface of separation. the object relative to the objective in order to
obtain an angular magnification of 30 when the
23. Define the magnifying power of a compound final image is formed at the near point.
microscope when the final image is formed at
infinity. Why must both the objective and the 30. Figure shows a convex spherical surface with
eyepiece of a compound microscope has a short centre of curvature C, separating the two media of
focal lengths? Explain. refractive indices n^ and n2. Draw a ray diagram
showing the formation of the image of a point
24. You are given two converging lens of focal lengths object O lying on the principal axis. Derive the
1.25 cm and 5 cm to design a compound relationship between the object and image
microscope. If it is desired to have a magnification distance in terms of refractive indices of the
of 30, find out the separation between the media and the radius of curvature R of the
objective and the eyepiece. surface.

25. Draw a labelled ray diagram of an astronomical

telescope to show the image formation of a
distant object. Write the main considerations
required in selecting the objective and the
eyepiece lenses in order to have large magnifying 31. An illuminated object and a screen are placed 90
power and high resolution of the telescope. cm apart. Determine the focal length and nature
of the lens required to produce a clear image on
the screen, twice the size of the object.
26. (i) Draw a labelled ray diagram showing the image
formation of a distant object by a refracting

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