# Physics MCQs for Class 12 Chapter 9 Ray Optics and Optical Instruments

Q.1. Which of the following colour 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 Answer: b

Q.2. 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 Answer: b

Q.3. 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 Answer: c

Q.4. Critical angle of glass is θ2 and that of water is θ2. The critical angle for water and glass surface would be (μg = 3/2, μw = 4/3).
(a) less than θ2
(b) between θ1 and θ2
(c) greater than θ2
(d) less than θ1

Answer Answer: c

Q.5. 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 Answer: d

Q.6. 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 Answer: b

Q.7. Which of the following forms a virtual and erect image for all positions of the object?
(a) Concave lens
(b) Concave mirror
(d) Convex mirror
(d) Both (a) and (c)

Answer Answer: d

Q.8. 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 Answer: c

Q.9. 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 Answer: a

Q.10. 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 Answer: d

Q.11. The field of view is maximum for
(a) plane mirror
(b) concave mirror
(c) convex mirror
(d) cylindrical mirror

Answer Answer: c

Q.12. A person is six feet tall. How tall must a plane mirror be if he is able to see his entire length?
(a) 3 ft
(b) 4.5 ft
(c) 7.5 ft
(d) 6 ft

Answer Answer: a

Q.13. The image formed by a concave mirror is
(a) always real
(b) always virtual
(c) certainly real if the object is virtual
(d) certainly virtual if the object is real

Answer Answer: c

Q.14. When light is refracted into a medium,
(a) its wavelength and frequency both increase
(b) its wavelength increases but frequency remains unchanged
(c) its wavelength decreases but frequency remains unchanged
(d) its wavelength and frequency both decrease

Answer Answer: b

Q.15. Which of the following phenomena is used in optical fibres ?
(a) Total internal reflection
(b) Scattering
(c) Diffraction
(d) Refraction

Answer Answer: a

Q.16. Critical angle of light passing from glass to water is minimum for
(a) red colour
(b) green colour
(c) yellow colour
(d) violet colour

Answer Answer: d

Q.17. If a glass prism is dipped in water, its dispersive power
(a) increases
(b) decreases
(c) does not change
(d) may increase or decrease depending on whether the angle of the prism is less than or greater than 60º

Answer Answer: b

Q.18. The objective of a telescope must be of large diameter in order to
(a) remove chromatic aberration
(b) remove spherical aberration and high magnification
(c) gather more light and for high resolution
(d) increase its range of observation

Answer Answer: c

Q.19. A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm 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 Answer: d

Q.20. To increase the angular magnification of a simple microscope, one should increase
(a) the focal length of the lens
(b) the power of the lens
(c) the aperture of the lens
(d) the object size

Answer Answer: b

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