CBSE Class 12 Physics Ray Optics and Optical Instruments MCQs Set B

Question. The direction of ray of light incident on a concave mirror is shown by PQ while directions in which the ray would travel after reflection is shown by four rays marked 1, 2, 3 and 4 (figure). Which of the four rays correctly shows the direction of reflected ray?

(a) 1
(b) 2
(c) 3
(d) 4

Answer : B

Question. Two thin lenses of focal lengths f₁ and f₂ are in contact and coaxial. Its power is same as power of a single lens given by

Answer : A

Question. How can the chromatic aberration be corrected
(a) By providing different suitable curvature to its two surface
(b) By combining it with another lens of opposite nature
(c) By reducing its aperture
(d) By providing proper polishing of its two surfaces

Answer : B

Question. When a beam of light from air enters into the water, the characteristics of light will not be changed, is :
(a) frequency
(b) speed
(c) colour
(d) amplitude

Answer : A

Question. A ray of light is incident at an angle of incidence, i, on one face of prism of angle A (assumed to be small) and emerges normally from the opposite face. If the refractive index of the prism is m, the angle of incidence i, is nearly equal to
(a) μA
(b) μA/2
(c) μ/A
(d) A/2μ

Answer : A

Question. A lens is made of flint glass (refractive index = 1.5). When the lens is immersed in a liquid of refractive index 1.25, the focal length:
(a) increases by a factor of 1.25
(b) increases by a factor of 2.5
(c) increases by a factor of 1.2
(d) decreases by a factor of 1.2

Answer : B

Question. A leaf which contains only green pigments, is illuminated by a laser light of wavelength 0.6328 mm. It wound appear to be:
(a) brown
(b) black
(c) red
(d) green

Answer : B

Question. The focal length of the objective and eye lenses of a microscope are 1.6 cm and 2.5 cm respectively.
The distance between the two lenses is 21.7 cm.
If the final image is formed at infinity, what is the linear magnification?
(a) 11
(b) 110
(c) 1.1
(d) 44

Answer : B

Question. A ray of light travelling in a transparent medium of refractive index m, falls on a surface separating the medium from air at an angle of incidence of 45°. For which of the following value of m the ray can undergo total internal reflection?
(a) m = 1.33
(b) m = 1.40
(c) m = 1.50
(d) m = 1.25

Answer : C

Question. Which of the following is false ?
(a) Convex lens always forms image with m < 1
(b) A simple mirror produces virtual, erect and same-sized image
(c) A concave mirror produces virtual, erect and magnified image
(d) A convex lens can produce real and same-sized image

Answer : A

Question. Which of the following is not the case with the image formed by a concave lens?
(a) It may be erect or inverted
(b) It may be magnified or diminished
(c) It may be real or virtual
(d) Real image may be between the pole and focus or beyond focus

Answer : D

Question. The intensity produced by a long cylindrical light source at a small distance r from the source is proportional to
(a) 1/r²
(b) 1r³
(c) 1/r
(d) None of the options

Answer : C

Question. If two mirrors are kept at 45° to each other and a body is placed in the middle then total number of images formed is :
(a) 7
(b) 8
(c) 14
(d) 4

Answer : A

Question. An astronomical telescope of ten fold angular magnification has a length of 44 cm. The focal length of the objective is :
(a) 44 cm
(b) 440 cm
(c) 40 cm
(d) 4 cm

Answer : C

Question. The refractive index of diamond is 2.0, velocity of light in diamond in cm per second is approximately :
(a) 1.5 × 10¹⁰
(b) 2.0 × 10¹⁰
(c) 6 × 10¹⁰
(d) 3 × 10¹⁰

Answer : A

Question. The critical angle for the material of a prism is 45°and its refracting angle is 30°. A monochromatic ray goes out perpendicular to the surface of emergence from the prism. Then the angle of incidence on the prism will be :
(a) 60°
(b) 75°
(c) 45°
(d) 30°

Answer : C

Question. A fish looking up through the water sees the outside world contained in a circular horizon. If the refractive index of water is 4/3 and the fish is 12 cm below the surface, the radius of this circle in cm is
(a) 36/√7
(b) 36 √7
(c) 4√ 5
(d) 36 √5

Answer : A

Question. A fish in an aquarium, 30 cm deep in water can see a light bulb kept 50 cm above the surface of water. The fish can also see the image of this bulb in the reflecting bottom surface of the aquarium. Total depth of water is 60 cm. Then the apparent distance between the two images seen by the fish is (mw = 4/3)
(a) 140 cm
(b) 760/3 cm
(c) 280/3 cm
(d) 380/3 cm

Answer : B

Question. The focal length of the objective and eye piece of a telescope are respectively 200 cm and 5 cm. The maximum magnifying power of the telescope will be
(a) – 100
(b) – 60
(c) – 48
(d) – 40

Answer : C

Question. A telescope has an objective lens of focal length 200 cm and an eye piece with focal length 2 cm.
If this telescope is used to see a 50 metre tall building at a distance of 2 km, what is the height of the image of the building formed by the objective lens?
(a) 5 cm
(b) 10 cm
(c) 1 cm
(d) 2 cm

Answer : A

Question. A ray of light incident at an angle q on a refracting face of a prism emerges from the other face normally. If the angle of the prism is 5° and the prism is made of a material of refractive index 1.5, the angle of incidence is
(a) 7.5°
(b) 5°
(c) 15°
(d) 2.5°

Answer : A

Question. You are given four sources of light each one providing a light of a single colour – red, blue, green and yellow. Suppose the angle of refraction for a beam of yellow light corresponding to a particular angle of incidence at the interface of two media is 90°. Which of the following statements is correct if the source of yellow light is replaced with that of other lights without changing the angle of incidence?
(a) The beam of red light would undergo total internal reflection
(b) The beam of red light would bend towards normal while it gets refracted through the second medium
(c) The beam of blue light would undergo total internal reflection
(d) The beam of green light would bend away from the normal as it gets refracted through the second medium

Answer : C

Question. The phenomena involved in the reflection of radiowaves by ionosphere is similar to
(a) reflection of light by a plane mirror
(b) total internal reflection of light in air during a mirage
(c) dispersion of light by water molecules during the formation of a rainbow
(d) scattering of light by the particles of air

Answer : B

Question. The optical density of turpentine is higher than tnat of water while its mass density is lower. Figure shows a layer of turpentine floating over water in a container. For which one of the four rays incident on turpentine in figure, the path shown is correct?
(a) 1
(b) 2
(c) 3
(d) 4

Answer : B

Question. The camera lens has an aperture of f and the exposure time is (1/60)s. What will be the new exposure time if the aperture become 1.4 f ?
(a) 1/42
(b) 1/56
(c) 1/72
(d) 1/31

Answer : D

Question. A thin glass (refractive index 1.5) lens has optical power of – 5 D in air. Its optical power in a liquid medium with refractive index 1.6 will be
(a) – 1D
(b) 1 D
(c) – 25 D
(d) 25 D

Answer : B

Question. A man 160 cm high stands in front of a plane mirror. His eyes are at a height of 150 cm from the floor. Then the minimum length of the plane mirrorfor him to see his full length image is C
(a) 85 cm
(b) 170 cm
(c) 80 cm
(d) 340 cm

Answer : C

Question. A green light is incident from the water to the air – water interface at the critical angle (q). Select the correct statement.
(a) The entire spectrum of visible light will come out of the water at an angle of 90º to the normal.
(b) The spectrum of visible light whose frequency is less than that of green light will come out to the air medium.
(c) The spectrum of visible light whose frequency is more than that of green light will come out to the air medium.
(d) The entire spectrum of visible light will come out of the water at various angles to the normal.

Answer : B

Question. Four lenses having the focal length of + 15 cm, 20 cm, +150 cm, and +250 cm respectively are provided to make an astronomical telescope. The focal length of the eyepiece to produce the largest magnification, should be :
(a) + 250 cm
(b) + 155 cm
(c) 25 cm
(d) + 15 cm

Answer : D

Question. The Cauchy’s dispersion formula is
(a) n = A + Bλ⁻¹ + Cλ⁻⁴
(b) n = A + Bλ² + Cλ⁻⁶
(c) n = A + Bλ⁻² + Cλ⁴
(d) n = A + Bλ² + Cλ⁴

Answer : A