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

Question. Sky appears to be blue in clear atmosphere due to which property of light :
(a) Scattering
(b) Polarization
(c) Diffraction
(d) Dispersion

Answer : A

Question. A doctor prescribes spectacles to a patient with a combination of a convex lens of focal length 40 cm, and concave lens of focal length 25 cm then the power of spectacles will be :
(a) – 6.5 D
(b) 1.5 D
(c) – 1.5 D
(d) – 8.5 D

Answer : C

Question. When a ray of light enters a glass slab, then
(a) its frequency and wavelength changes
(b) its frequency does not change
(c) only frequency changes
(d) its frequency and velocity changes

Answer : B

Question. An equilateral prism is made of a material of refractive index 3 . The angle of minimum deviation for the prism is
(a) 90°
(b) 60°
(c) 45°
(d) 30°

Answer : B

Question. A thin prism P1 with angle 6° and made froM glass of refractive index 1.54 is combined with another thin prism P2 of refractive index 1.72 to produce dispersion without deviation. The angle of prism P2 will be
(a) 4° 30′
(b) 8.5°
(c) 6.5°
(d) None of the options

Answer : A

Question. The focal length of a converging lens are fV and fR for violet and red light respectively. Then
(a) fV > fR
(b) fV = fR
(c) fV < fR
(d) any of the three is

Answer : C

Question. A plano-convex lens of focal length 30 cm has its plane surface silvered. An object is placed 40 cm from the lens on the convex side. The distance of the image from the lens is B
(a) 18 cm
(b) 24 cm
(c) 30 cm
(d) 40 cm

Answer : B

Question. An endoscope is employed by a physician to view the internal parts of a body organ. It is based on the principle of :
(a) refraction
(b) reflection
(c) total internal reflection
(d) dispersion

Answer : C

Question. An object approaches a convergent lens from the left of the lens with a uniform speed 5 m/s and stops at the focus. The image
(a) moves away from the lens with an uniform speed 5 m/s
(b) moves away from the lens with an uniform acceleration
(c) moves away from the lens with a non-uniform acceleration
(d) moves towards the lens with a non-uniform acceleration

Answer : C

Question. A short pulse of white light is incident from air to a glass slab at normal incidence. After travelling through the slab, the first colour to emerge is
(a) blue
(b) green
(c) violet
(d) red

Answer : D

Question. A passenger in an aeroplane shall
(a) never see a rainbow
(b) may see a primary and a secondary rainbow as concentric circles
(c) may see a primary and a secondary rainbow as concentric arcs
(d) shall never see a secondary rainbow

Answer : D

Question. The radius of curvature of the curved surface of a planoconvex lens is 20 cm. If the refractive index of the material of the lens be 1.5, it will
(a) act as a convex lens only for the objects that lie on its curved side
(b) act as a concave lens for the objects that lie on its curved side
(c) act as a convex lens irrespective of the side on which the object lies
(d) act as a concave lens irrespective of side on which the object lies

Answer : C

Question. An object is immersed in a fluid. In order that the object becomes invisible, it should :
(a) behave as a perfect reflector
(b) absorb all light falling on it
(c) have refractive index one
(d) have refractive index exactly matching with that of the surrounding fluid

Answer : D

Question. Sodium lamps are used in foggy conditions because :
(a) yellow light is scattered less by the fog particles
(b) yellow light is scattered more by the fog particles
(c) yellow light is unaffected during its passage through the fog
(d) Wavelength of yellow light is the mean of the visible part of the spectrum

Answer : A

Question. In refraction, light waves are bent on passing from one medium to the second medium, because, in the second medium:
(a) the frequency is different
(b) the coefficient of elasticity is different
(c) the speed is different
(d) the amplitude is smaller

Answer : C

Question. 1 wire mesh consisting of very small squares is viewed at a distance of S cm through a magnifying converging lens of focal length 10 cm, kept close to the eye. The magnification produced by the lens is:
(a) 5
(b) 8
(c) 10
(d) 20

Answer : A

Question. An astronomical telescope has a large aperture to
(a) reduce spherical aberration
(b) have high resolution
(c) increase span of observation
(d) have low dispersion

Answer : B

Question. A lamp of 250 candle power is hanging at a distance of 6 m from a wall. The illuminance at a point on the wall at a minimum distance from lamp will be
(a) 9.64 lux
(b) 4.69 lux
(c) 6.94 lux
(d) None of the options

Answer : C

Question. The critical angle for light going from medium X into medium Y is q. The speed of light in medium X is v, then speed of light in medium Y is
(a) v(1 – cos θ)
(b) v/sin θ
(c) v/cos θ
(d) v cos θ

Answer : B

Question. The refractive index of a piece of transparent quartz is the greatest for
(a) violet light
(b) red light
(c) green light
(d) yellow light

Answer : A

Question. Mirage is a phenomenon due to :
(a) refraction of light
(b) diffraction of light
(c) total internal reflection of light
(d) None of the options

Answer : C

Question. In an astronomical microscope, the focal length of the objective is made :
(a) shorter than that of the eye piece
(b) greater than that of the eye piece
(c) half of the eye piece
(d) equal to that of the eye piece

Answer : B

Question. Light appears to travel in a straight line, because
(a) its wavelength is very small
(b) its velocity is large
(c) it is not absorbed by surroundings
(d) it is reflected by surroundings

Answer : A

Question. A concave mirror having the focal length 15 cm, forms an image having twice of the linear dimensions of the object. If the image is virtual, then the position of the object will be :
(a) 7.5 cm
(b) 22.5 cm
(c) 40 cm
(d) 30 cm

Answer : A

Question. An achromatic convergent lens of focal length 20 cms is made of two lenses (in contact) of materials having dispersive powers in the ratio of 1 : 2 and having focal lengths f1 and f2. Which of the following is true ?
(a) f1 = 10 cms, f2 = –20 cms
(b) f1 = 20 cms, f2 = 10cms
(c) f1 = –10 cms, f2 = –20 cms
(d) f1 = 20 cms, f2 = –20 cms

Answer : A

Question. In total internal reflection when the angle of incidence is equal to the critical angle for the pair of media in contact, what will be angle of refraction?
(a) 90°
(b) 180°
(c) 0°
(d) equal to angle of incidence

Answer : A

Question. Which of the following is not due to total internal reflection?
(a) Working of optical fibre
(b) Difference between apparent and real depth of a pond
(c) Mirage on hot summer days
(d) Brilliance of diamond

Answer : B

Question. 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 : D

Question. A plane mirror reflects a beam of light to form a real image. The incident beam is
(a) parallel
(b) convergent
(c) divergent
(d) any one of the above

Answer : B

Question: A small source of light is 4 m below the surface of water of refractive index 5/3. In order to cut off all the light, coming out of water surface, minimum diameter of the disc placed on the surface of water is
(a) 6 m
(b) ∞
(c) 3 m
(d) 4 m
Answer: b

Question: A disc is placed on a surface of pond which has refractive index 5/3. A source of light is placed 4 m below the surface of liquid. The minimum radius of disc needed so that light is not coming out is,
(a) ∞
(b) 3 m
(c) 6 m
(d) 4 m
Answer: b

Question: If the focal length of objective lens is increased then magnifying power of
(a) microscope will increase but that of telescope decrease
(b) microscope and telescope both will increase
(c) microscope and telescope both will decrease
(d) microscope will decrease but that of telescope will increase 
Answer: d

Question: If a convex lens of focal length 80 cm and a concave lens of focal length 50 cm are combined together, what will be their resulting power?
(a) + 7.5 D
(b) –0.75 D
(c) + 6.5 D
(d) –6.5 D
Answer: b

Question: The refractive index of the material of a prism is √2 and the angle of the prism is 30°. One of the two refracting surfaces of the prism is made a mirror inwards, by silver coating. A beam of monochromatic light entering the prism from the other face will retrace its path (after reflection from the silvered surface) if its angle of incidence on the prism is
(a) 60°
(b) 45°
(c) 30°
(d) zero
Answer: b

Question: For a normal eye, the cornea of eye provides a converging power of 40 D and the least converging power of the eye lens behind the cornea is 20 D. Using this information, the distance between the retina and the cornea-eye lens can be estimated to be
(a) 1.67 cm
(b) 1.5 cm
(c) 5 cm
(d) 2.5 cm
Answer: a

Question: The focal length of converging lens is measured for violet, green and red colours. It is respectively f_v, f_g, f_r . We will get
(a) f_v < f_r
(b) f_g > f_r
(c) f_v = f_g
(d) f_g < f_r
Answer: a

Question: Four lenses of focal length ±15 cm and ±150 cm are available for making a telescope. To produce the largest magnification, the focal length of the eyepiece should be
(a) +15 cm
(b) +150 cm
(c) –150 cm
(d) –15 cm
Answer: a

Question: A ray of light travelling in air have wavelength λ, frequency n, velocity v and intensity I. If this ray enters into water then these parameters are λ′, n′, v′ and I′ respectively. Which relation is correct from following?
(a) λ = λ′
(b) n = n′
(c) v = v′
(d) I = I′ 
Answer: b

Question: Match the corresponding entries of Column 1 with Column 2. [Where m is the magnification produced by the mirror]
Column 1                     Column 2
(A) m = –2             (p) Convex mirror
(B) m= − 1/2         (q) Concave mirror
(C) m = + 2           (r) Real image
(D) m= + 1/2         (s) Virtual image
(a) A → p and s; B → q and r; C → q and s; D → q and r
(b) A → r and s; B → q and s; C → q and r; D → p and s
(c) A → q and r; B → q and r; C → q and s; D → p and s
(d) A → p and r; B → p and s; C → p and q; D → r and s 
Answer: c