WORKSHEET 9.

4 2 MARK QUESTIONS
1] Use the mirror equation to show that an object placed between f and 2f of
a concave mirror produces a real image beyond 2f.
2] Draw a ray diagram to show image. Formation when the concave mirror
produces a real, inverted and magnified image of the object.
3] The refractive index of diamond is much higher than that of glass. How does
a diamond cutter make use of this fact?

4) When monochromatic light travels from one medium to another, its

wavelength changes but frequency remains same. Explain.
5] A biconvex lens made of a transparent material of refractive index 1.25 is
immersed in water of refractive index 1.33. Will the lens behave as a
converging or a diverging lens? Give reason.
6]Find the radius of curvature of the convex surface of a plano-convex lens,
whose focal length is 0.3 m and the refractive index of the material of the lens
is 1.5
7]What is the focal length of a focal convex lens of length 30 cm in contact
with a lens of focal length 20 cm? Is the system a converging lens or diverging
lens? Ignore thickness of the lens.
8]The image obtained with a convex lens is erect and its length is four times
the length of the object. If the focal length of the lens is 20 cm, calculate the
object and image distances.
9]Explain two advantages of a reflecting telescope over a refracting telescope
10)Consider a telescope whose objective lens has a focal length of 100 cm and
the eyepiece has focal length 1 cm. What will be the magnification of the given
telescope?
11]Two lenses of focal lengths 6 cm and 50 cm are to be used for making a
telescope. Which will you see for the objective?
12] A candle flame is held 3 cm away from concave mirror of radius of
Curvature 24 cm. Where is the image formed? What is the nature of the image?

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13]An object is placed in front of a convex mirror of focal length 30 cm. If the
image is a quarter of the size of the object, find the position of the image.
14] A ray of light is incident at an angle of 60° on one face of a rectangular
glass slab of thickness 0.1 m and refractive index 1.5. Calculate the lateral
shift produced.
15]Light from a point source in air falls on a spherical glass surface (n = 1.5
and radius of curvature 20 cm). The distance of the light source from the glass
surface is 100 cm. At what position the image is formed?
16]A convergent beam of light passes through the diverging lens of focal
length 0.2 m and comes to focus 0.3 m behind the lens. Find the position of
the point at which the beam would converge in the absence of the lens.
17]The radii of curvature of the surfaces of a double convex lens are 20 cm
and 40 cm, respectively and its focal length is 20 cm. What is refractive index
of the material of the lens?

18]Two thin lenses are in contact and the focal length of the combination is
80 cm. If the focal length of one lens is 20 cm, then what would be the power
of the other lens?

19) A telescope consists of two lenses of focal lengths 20 cm and 5 cm. Obtain
its magnifying power when the final image is (i)at infinity (iljat 25 cm from the
lenses of eye.
20] A convex lens of focal length 5 cm is used as a simple microscope. What
will be the magnifying power when the image is formed at the least distance
of distinct vision?
 WORKSHEET 9.5 3 MARK QUESTIONS
1] A ray of light suffers minimum deviation, while passing through a prism of
refractive index 1.5 and refractive angle 600, Calculate the angle of deviation
and angle of incidence. (Given, sin-'(0.75) = 48.69)
2] A compound microscope has an objective of focal length of 1 cm and an
eyepiece of focal length 2.5 cm. An object has to be placed at a distance of 1.2
cm away from the objective for the normal adjustment. Determine the angular
magnification and length of the microscope tube.
3] An object AB is kept in front of a concave mirror as shown in the figure.

B C

(i) Complete the ray diagram showing e image formation of the object.

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RAY OPTICS AND OPTICAL INSTRUMENTS

(ii) How will the position and intensity or image be affected, if the lower half
of the mirror's reflecting surface is painted black?
4)When monochromatic light travels from a rarer to a denser medium, explain
the following, giving reasons.
(i) Is the frequency of reflected and refracted light same as the frequency of
incident light?
(i) Does the decrease in speed imply reduction in the energy carried by the
light wave?

5) (i) Write the necessary conditions for the phenomenon of total internal
reflection to OCcur.

(i) Write the relation between refractive index and critical angle for a given
pair of optical media.
6) The figure shows a ray of light falling normally on the face AB of an
equilateral glass prism having refractive index 3/2, placed in water of
refractive index 4/3. Will this ray suffer total internal reflection on striking
the face AC? Justify your answer.

7]Define power of a lens. Write its units. Deduce the relation for
two thin lenses kept in contact coaxially.
8] The objective of an astronomical telescope has a diameter of 150 mm and
a focal length of 4 m. The eyepiece has a focal length of 25 mm. Calculate the
magnifying and resolving power of telescope (wavelength= 6000 Ä for yellow
colour).
9]Draw a labelled ray diagram showing the formation of a final image by a
Compound microscope at least distance of distinct vision.

10] Asmall telescope has an objective lens of focal length 150 cm and eyepiece
of focal length 5 cm. What is the magnifying power of the telescope for viewing
distant objects in normal adjustments?If this telescope is used to viewa 100
m tall tower 3 km away, then what is the height of the tower formed by the
objective lens?
WORKSHEET 9.6 5 MARK QUESTIONS

KENDRIYA VIDYALAYA NO.2 BELAGAVICANTT 263

RAY OPTICS AND OPTICAL INSTRUMENTS

1] (a) Draw a ray diagram to show image formation when the concave mirror
produces a real, inverted and magnified image of the object.
(b) Obtain the mirror formula and write the expression for the linear
magnification.
2] Explain the phenomenon of total internal reflection. Describe how TIR takes
place in optical fibre. State any 2 uses of it.
3] Three light rays, red (R), green (G) and blue (B) are incident on a right angled
prism ABC at face AB. The refractive indices of the material of the prism for
red, green and blue wavelengths are I.39, I.44 and 1.47 respectively. Out of
the three, which colour of ray will emerge out of face AC? Justify your answer.
Trace the path of these rays after passing through face AB.

4] (i) Draw a neat labelled ray diagram of a compound microscope. Explain

briefly its working.
(ii) Why must both the objective and the eyepiece ofa compound microscope
have short focal lengths?
5] Draw a labelled ray diagram of a refracting telescope. Define its magnifying
power and write the expression for it. Write 2 important limitations of a
refracting telescope over a reflecting type telescope.
6] A ray PQ of light is incident on the face AB of a glass prism ABC (as shown
in the figure) and emerges out of face AC. Trace the path of the ray. Show that
ite= A+6 where 6 ande denote the angle of deviation and the angle of
emergence, respectively.

Plot a graph showing the variation of the angle of deviation as a function of

angle of incidence. State the condition under which 6 is minimum.