MCQ On Class 12 Physics Chapter 9 Ray Optics and Optical Instruments

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Questions
1 An astronomical refractive telescope has an objective of focal length 20 m and an eyepiece of focal length 2 cm. Then
A the magnification is 1000
B the length of the telescope tube is 20.02 m
C the image formed of inverted
D all of these

Answer:all of these
2 Two beams of red and violet color are made to pass separately through a prism (angle of the prism is 60°). In the position of minimum deviation, the angle of refraction will be
A 30° for both the colors
B greater for the violet color
C greater for the red color
D equal but not 30° for both the colors

Answer:30° for both the colors
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3 Which of the following forms a virtual and erect image for all positions of the object?
A Concave lens
B Concave mirror
C Convex mirror
D Both (a) and (c)

Answer:Both (a) and (c)
4 Mirage is a phenomenon due to
A refraction of light
B reflection of light
C total internal reflection of light
D diffraction of light.

Answer:total internal reflection of light
5 Two lenses of focal lengths 20 cm and – 40 cm are held in contact. The image of an object at infinity will be formed by the combination at
A 10 cm
B 20 cm
C 40 cm
D infinity

Answer:40 cm
6 Which of the following colours of white light deviated most when passes through a prism?
A Red light
B Violet light
C Yellow light
D Both (a) and (b)

Answer:Violet light
7 A convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens. Then its focal length will
A become zero
B become infinite
C become small, but non-zero
D remain unchanged

Answer:become infinite
8 An under-water swimmer cannot see very clearly even in absolutely clear water because of
A absorption of light in water
B scattering of light in water
C reduction of speed of light in water
D change in the focal length of eye lens

Answer:change in the focal length of eye lens
9 For a total internal reflection, which of the following is correct?
A Light travels from rarer to denser medium.
B Light travels from denser to rarer medium.
C Light travels in air only.
D Light travels in water only.

Answer:Light travels from denser to rarer medium.
10 A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 ’em in such a way that its end closer to the pole is 20 cm away from the mirror. The length of the image is
A 10 cm
B 15 cm
C 2.5 cm
D 5 cm

Answer:5 cm
11 The branch of optics dealing with the formation of images using the concept of straight line propagation of light is called:
A geometrical optics
B physical optics
C corpuscular optics
D quantum optics

Answer:quantum optics
12 The air bubble inside water shine due to:
A Reflection
B Refraction
C T.l.R.
D None of these

Answer:T.l.R.
13 When light travels from one medium to another, which of the following does not change?
A frequency
B refractive index
C velocity
D wavelength

Answer:frequency
14 A thin glass (RI = 3/2) lens has optical power of – 5D in air. Its optical power in a liquid medium with RI = 1.6 will be:
A -2.5 D
B 25 D
C -ID
D 0.625 D

Answer:0.625 D
15 The refractive indices (R.I.) of glass and water with respect to air are 3/2 and 4/3 respectively. The R.I. of glass w.r. to w ater is:
A 8/9
B 9/8
C 7/6
D 2

Answer:9/8
16 A convergent lens will become less convergent in :
A oil
B water
C both of (a) and (b)
D none of these

Answer:water
17 If a mirror is approaching you at a speed of 10 ms^1, the speed with which your image approach you is:
A 10 ms-1
B 5 ms-1
C 20 ms-1
D 15 ms-1

Answer:20 ms-1
18 Which of the following cannot be polarised?
A radiowaves
B transverse waves
C sound waves
D X-rays

Answer:sound waves
19 Two lens of power -15 D and +5 D are placed in contact co-axially. The focal length of equivalent lens is:
A -10 cm
B -20 cm
C +10 cm
D None

Answer:-10 cm
20 When a ray of light (white) enters a lens, undergoes a change is:
A wavelength
B velocity
C frequency
D both velocity and wavelength

Answer:both velocity and wavelength

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