TEXT BOOK EVALUATION
I. Book Exercise – Choose the best answer
1. The refractive index of four substances A, B, C and D are 1.31, 1.43, 1.33, 2.4 respectively. The speed of light is maximum in
a. A b. B c. C d. D
Ans : (a) A
2. Where should an object be placed so that a real and inverted image of same size is obtained by a convex lens
a. f b.
2f c. infinity d. between f and 2f
Ans : (b) 2f
3. A small bulb is placed at the principal focus of a convex lens. When the bulb is switched on, the lens will produce
a. a convergent beam of light b. a divergent beam of light
c. a parallel beam of light d. a coloured beam of
light
Ans : (c) a parallel beam of light
4. Magnification of a convex lens is
a. positive b. negative
c. either positive or negative d. zero
Ans : (c) either positive or negativee
5. A convex lens forms a real, diminished point sized image at focus. Then the position of the object is at
a. focus b. infinity c. at 2f d.
between f and 2f
Ans : (b) infinity
6. Power of a lens is –4D, then its focal length is
a. 4m b. –40 m c. –0.25 m d. –2.5 m
Ans : (c) –0.25 m
Unit-2: Optics GANGA t Science (Physics) 29
7. In a myopic eye, the image of the object is formed
a. behind the retina b. on the retina c. in front of
the retina d. on the blind spot
Ans : (c) in front of the retina
8. The eye defect ‘presbyopia’ can be corrected by
a. convex lens
b. concave lens c.
convex mirror d. bi focal lenses
Ans : (d) bi focal lenses
9. Which of the following lens would you prefer to use while reading small letters found in a dictionary?
a. A convex lens of focal length 5 cm b.A concave lens of focal length 5
cm
c.A convex lens of focal length 10 cm d. A concave lens of focal length
10 cm
Ans : (a) A convex lens of focal length 5 cm
10. If VB, VG, VR be the velocity of blue, green and red light respectively in a glass prism, then which of the following statement gives the correct relation?
a. VB = VG = VR b. VB > VG > VR c. VB < VG
< VR d. VB < VG > VR
Ans : (b) VB > VG > VR
II. Book Exercise – Fill in the blanks
1. The path of the light is called as __________. Ans
: ray
2.
The refractive index of a transparent medium is always greater than __________ Ans : one
3. If the energy of incident beam and the scattered
beam are same, then the scattering of light is called as
__________ scattering. Ans : Elastic
4. According to Rayleigh’s scattering law, the amount
of scattering of light is inversely proportional to the fourth
power of its __________. Ans : wave length
5. Amount of light entering into the eye is controlled
by __________. Ans : iris
III. Book Exercise – True or False (If false correct
it)
1. Velocity of light is greater in denser medium than
in rarer medium.
Ans : False. Velocity of light is greater in rare
medium than in denser medium.
2. The power of lens depends on the focal length of
the lens.
Ans : True.
3. Increase in the converging power of eye lens cause
‘hypermetropia’.
Ans : True.
4. The convex lens always gives small virtual image.
Ans : False. Only concave lens always gives small
virtual image.
IV. Book Exercise – Match the following
Column I Column II
1. Retina
(a) Path way of light
2. Pupil (b) Far point comes closer
3. Ciliary muscles (c) Near point moves away
4. Myopia (d) Screen of the eye
5. Hypermetropia (e) Power of accomodation
Ans :
Column I
Column II
1 Retina d Screen of the eye
2 Pupil b Path way of light
3 Ciliary muscles f Power of accomodation
4 Myopia b Far point comes closer
5 Hypermetropia c Near point moves away
30 GANGA t Science (Physics) Xth Std t Unit-2
V. Book Exercise – Assertion and Reason
Mark the correct choice as
a) If both the assertion and the reason are true and the reason is the correct explanation of assertion.
b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
c) Assertion is true, but the reason is false.
d) Assertion is false, but the reason is true.
1. Assertion: If the refractive index of the medium is high (denser medium) the velocity of the light in that medium will be small.
Reason: Refractive index of the medium is inversely
proportional to the velocity of the light.
Ans : (a) both the assertion and the reason are true
and the reason is the correct explanation of assertion.
2. Assertion: Myopia is due to the increase in the
converging power of eye lens.
Reason: Myopia can be corrected with the help of
concave lens.
Ans : (b) both the assertion and the reason are true,
but the reason is not the correct explanation of the assertion 
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