Optics

Samacheer Book Back Questions And Answers For Science Standard 10 “Optics“

I. Choose the correct 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

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

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

4. Magnification of a convex lens is
a) Positive
b) negative
c) either positive or negative
d) zero

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

6. Power of a lens is –4D, then its focal length is
a) 4m
b) –40m
c) –0.25 m
d) –2.5 m

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

8. The eye defect ‘presbyopia’ can be corrected by
a) convex lens
b) concave lens
c) convex mirror
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

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

II. Fill in the blanks:
1. The path of the light is called as _____.
2. The refractive index of a transparent medium is always greater than _____.
3. If the energy of incident beam and the scattered beam are same, then the scattering of light is called as _____ scattering.
4. According to Rayleigh’s scattering law, the amount of scattering of light is inversely proportional to the fourth power of its _____.
5. Amount of light entering into the eye is controlled by _____.

Answers:
1. ray
2. one
3. elastic
4. wavelength
5. Iris

III. True or False. If false correct it:
1. Velocity of light is greater in denser medium than in rarer medium.
2. The power of lens depends on the focal length of the lens.
3. Increase in the converging power of eye lens cause ‘hypermetropia’.
4. The convex lens always gives small virtual image.

Answers:
1. False (Velocity of light is lesser in denser medium than in rarer medium)
2. True
3. True
4. False (Concave lens always gives small virtual image)

IV. Match the following:
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 accommodation

Answers:
1. D
2. A
3. E
4. B
5. C

V Assertion and reasoning type:
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
a) If both assertion and reason are true and reason is the correct explanation of assertion.
b) If both assertion and reason are true but reason is not the correct explanation of assertion.
c) Assertion is true but reason is false.
d) Assertion is false but reason is true.

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.
a) If both assertion and reason are true and reason is the correct explanation of assertion.
b) If both assertion and reason are true but reason is not the correct explanation of assertion.
c) Assertion is true but reason is false.
d) Assertion is false but reason is true.