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

Students of class 12 Physics should refer to MCQ Questions Class 12 Physics Ray Optics and Optical Instruments with answers provided here which is an important chapter in Class 12 Physics NCERT textbook. These MCQ for Class 12 Physics with Answers have been prepared based on the latest CBSE and NCERT syllabus and examination guidelines for Class 12 Physics. The following MCQs can help you to practice and get better marks in the upcoming class 12 Physics examination

## Chapter 9 Ray Optics and Optical Instruments MCQ with Answers Class 12 Physics

MCQ Questions Class 12 Physics Ray Optics and Optical Instruments provided below have been prepared by expert teachers of grade 12. These objective questions with solutions are expected to come in the upcoming Standard 12 examinations. Learn the below provided MCQ questions to get better marks in examinations.

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 (Fig. given alongside). Which of the four rays correctly shows the direction of reflected ray?

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

B

Question. The sky would appear red instead of blue if
(a) atmospheric particles scatter blue light more than red light
(b) atmospheric particles scatter all colours equally
(c) atmospheric particles scatter red light more than blue light
(d) the sun was much hotter

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

D

Question. An object is placed at a distance of 40 cm from a concave mirror of focal length 15 cm. If the object is displaced through a distance of 20 cm towards the mirror, the displacement of the image will be
(a) 30 cm away from the mirror
(b) 36 cm away from the mirror
(c) 30 cm towards the mirror
(d) 36 cm towards the mirror

D

Question. The reddish appearance of rising and setting sun is due to
(a) reflection of light
(b) diffraction of light
(c) scattering of light
(d) interference of light

C

Question. The optical density of turpentine is higher than that 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 the figure, the path shown is correct?

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

B

Question. Why is refractive index in a transparent medium greater than one?
(a) Because the speed of light in vacuum is always less than speed in a transparent medium
(b) Because the speed of light in vacuum is always greater than the speed in a transparent medium
(c) Frequency of wave changes when it crosses medium
(d) None of the above

B

Question. A concave mirror of focal length 15 cm forms are image having twice the linear dimensions of the object. The position of the object, when the image is virtual, will be
(a) 22.5 cm
(b) 7.5 cm
(c) 30 cm
(d) 45 cm

B

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.

C

Question. The radius of curvature of the curved surface of a plano-convex 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.

C

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

A

Question. A student measures the focal length of a convex lens by putting an object pin at a distance ‘u’ from the lens and measuring the distance ‘v’ of the image pin. The graph between ‘u’ and ‘v’ plotted by the student should look like

A

Question. Focal length of a convex lens of refractive index 1.5 is 2 cm. Focal length of lens, when immersed in a liquid of refractive index of 1.25 will be
(a) 10 cm
(b) 7.5 cm
(c) 5 cm
(d) 2.5 cm

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 accleration.
(c) moves away from the lens with a non-uniform acceleration.
(d) moves towards the lens with a non-uniform acceleration.

C

Question. An equiconvex lens is cut into two halves along (i) XOX’ and (ii) YOY ‘ as shown in the figure. Let f, f ‘ and f ” be the of the focal lengths of complete lens of each half in case (i) and of each half in case (ii) respectively. Choose the correct statement from the following :

(a) f ‘ = 2 f and f ” = f
(b) f ‘ = f and f ” = f
(c) f ‘ = 2 f and f ” = 2 f
(d) f ‘ = f and f ” = 2 f

D

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 it path (after reflection from the silvered surface) if its angle of incidence of the prism is
(a) 60°
(b) 45°
(c) 30°
(d) zero

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

D

Question. The magnifying power of a telescope is 9. When it is adjusted for parallel rays the distance between the objective and eyepiece is 20 cm. The focal length of lenses are
(a) 11 cm, 9 cm
(b) 10 cm, 10 cm
(c) 15 cm, 5 cm
(d) 18 cm, 2 cm

D

Question. A beam of light consisting of red, green and blue colours is incident on a right angled prism. The refractive index of the material of the prism for the above red, green and blue wavelengths are 1.39, 1.44 and 1.47 respectively. The prism will

(a) not separate the three colours at all
(b) separate the red colour part from the green and blue colours
(c) separate the blue colour part from the red and green colours
(d) separate all the three colours from one another

B

Question. A thin prism having refracting angle 10° is made of glass of refractive index 1.42. This prism is combined with another thin prism of glass of refractive index 1.7. This combination produces dispersion without deviation. This refracting angle of second prism should be
(a) 6°
(b) 8°
(c) 10°
(d) 4°

A

Question. Transmission of light in optical fibre is due to
(a) scattering
(b) diffraction
(c) refraction
(d) multiple total internal reflection

D

Question. A setting sun appears to be at an altitude higher than it really is. This is because of
(a) absorption of light
(b) reflection of light
(c) refraction of light
(d) dispersion of light

C

Question. For relaxed eye, the magnifying power of a microscope is

A

Question. A normal eye is not able to see objects closer than 25 cm because
(a) the focal length of the eye is 25 cm
(b) the distance of the retina from the eye-lens is 25 cm
(c) the eye is not able to decrease the distance between the eye-lens and the retina beyond a limit
(d) the eye is not able to decrease the focal length beyond a limit

D

Question. What will be the colour of the sky as seen from the earth if there were no atmosphere?
(a) Black
(b) Blue
(c) Orange
(d) Red

A

Question. A vessel of depth 2d cm is half filled with a liquid of refractive index μ1 and the upper half with a liquid of refractive index μ2. The apparent depth of the vessel seen perpendicularly is

B

Question. The one parameter that determines the brightness of a light source sensed by an eye is
(a) energy of light entering the eye per second
(b) wavelength of the light
(c) total radiant flux entering the eye
(d) total luminous flux entering the eye

D

Question. Resolving power of a telescope increases with
(a) increase in focal length of eye-piece
(b) increase in focal length of objective
(c) increase in aperture of eye piece
(d) increase in apeture of objective

D

Question. In vacuum the speed of light depends upon
(a) frequency
(b) wavelength
(c) velocity of light sources
(d) None of these

D

Question. Rectilinear motion of light in a medium is caused due to
(a) high frequency
(b) short wavelength
(c) velocity of light
(d) uniform refractive index of the medium

D

Question. The distance between an object and its real image formed by a convex lens cannot be
(a) greater than 2 f
(b) less than 2 f
(c) greater than 4 f
(d) less than 4 f

D

Question. In a concave mirror, an object is placed at a distance x1 from focus, and image is formed at a distance x2 from focus. Then focal length of mirror is

A

Question. An electromagnetic radiation of frequency n, wavelength l, travelling with velocity v in air enters in a glass slab of refractive index (μ). The frequency, wavelength and velocity of light in the glass slab will be respectively

A

Question. 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) remain unchanged
(b) become zero
(c) become infinite
(d) become small, but non-zero

C

Question. The index of refraction of diamond is 2.0. The velocity of light in diamond is approximately
(a) 1.5 × 1010 cm/sec
(b) 2 × 1010 cm/sec
(c) 3.0 × 1010 cm/sec
(d) 6 × 1010 cm/sec

A

Question. The luminous intensity of 100 W unidirectional bulb is 100 candela. The total luminous flux emitted from bulb will be
(a) 100 π lumen
(b) 200 π lumen
(c) 300 π lumen
(d) 400 π lumen

D

Question. A convex lens of focal length f1 and a concave lens of focal length f2 are placed in contact. The focal length of the combination is

C

Question. A lens of power + 2 diopter is placed in contact with a lens of power – 1 diopter. The combination will behave like
(a) a convergent lens of focal length 50 cm
(b) a divergent lens of focal length 100 cm
(c) a convergent lens of focal length 100 cm
(d) a convergent lens of focal length 200 cm

C

Question. The focal length of the objective of a telescope is 60 cm. To obtain a magnification of 20, the focal length of the eye piece should be
(a) 2 cm
(b) 3 cm
(c) 4 cm
(d) 5 cm

B

Question. A beam of light consisting of red, green and blue colours is incident on a right-angled prism as shown. The refractive index of the material of the prism for the above red, green and blue wavelengths are 1.39, 1.44 and 1.47 respectively. The prism will

(a) f/2
(b) f
(c) 2 f
(d) 4 f

B

Question. A real image is formed by a convex lens. If we put a concave lens in contact with it, the combination again forms a real image. The new image
(a) is closer to the lens system.
(b) is farther form the lens system.
(c) is at the original position.
(d) may be anywhere depending on the focal length of the concave lens.

B

Question. Two convex lenses of focal lengths 0.3 m and 0.05 m are used to make a telescope. The distance kept between the two in order to obtain an image at infinity is
(a) 0.35 m
(b) 0.25 m
(c) 0.175 m
(d) 0.15 m

A

Question. An object is placed at a distance of 40 cm in front of a concave mirror of focal length 20 cm. The image produced is
(a) real, inverted and smaller in size
(b) real, inverted and of same size
(c) real and erect
(d) virtual and inverted

B

Question. A ray incident at 15° on one refracting surface of a prism of angle 60° suffers a deviation of 55°. What is the angle of emergence ?
(a) 95°
(b) 45°
(c) 30°
(d) None of these

D

Question. A rectangular block of glass is placed on a mark made on the surface of the table and it is viewed from the vertical position of eye. If refractive index of glass be μ and its thickness d, then the mark will appear to be raised up by

B

Question. A glass slab of thickness 4 cm contains the same number of waves as 5 cm of water when both are traversed by the same monochromatic light. If the refractive index of water is 4/3, what is that of glass?
(a) 5/3
(b) 5/4
(c) 16/15
(d) 1.5

Question. It is desired to photograph the image of an object placed at a distance of 3 m from plane mirror. The camera, which is at a distance of 4.5 m from mirror should be focussed for a distance of
(a) 3 m
(b) 4.5 m
(c) 6 m
(d) 7.5 m

D

Question. An air bubble in glass slab (μ = 1.5) from one side is 6 cmand from other side is 4 cm. The thickness of glass slab is
(a) 10 cm
(b) 6.67 cm
(c) 15 cm
(d) None of these

C

Question. A man’s near point is 0.5 m and far point is 3 m. Power of spectacle lenses required for (i) reading purposes, (ii) seeing distant objects, respectively, are
(a) –2 D and + 3 D
(b) +2 D and –3 D
(c) +2 D and –0.33 D
(d) –2 D and + 0.33 D

C

Question. Light passes through a glass plate of thickness d and refractive index m. For small angle of incidence i, the lateral displacement is

C

Question. Two light sources with equal luminous intensity are lying at a distance of 1.2 m from each other. Where should a screen be placed between them such that illuminance on one of its faces is four times that on another face ?
(a) 0.2 m
(b) 0.4 m
(c) 0.8 m
(d) 1.6 m

C

Question. A vessel is half filled with a liquid of refractive index μ. The other half of the vessel is filled with an immiscible liquid of refrative index 1.5 μ. The apparent depth of the vessel is 50% of the actual depth. Then m is
(a) 1.4
(b) 1.5
(c) 1.6
(d) 1.67

D

Question. A lamp is hanging along the axis of a circular table of radius r. At what height should the lamp be placed above the table,
so that the illuminance at the edge of the table is 1/8 of that at its centre?
(a) r/2
(b) r /√2
(c) r/3
(d) r /√3

D

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 mirror for him to see his full length image is
(a) 85 cm
(b) 170 cm
(c) 80 cm
(d) 340 cm

C

Fill in the Blanks [1 mark]

Question. The amount of scattering is inversely proportional to the _________________ power of the wavelength.

fourth

Question. When the refractive index of the material of the lens is greater than that of the surroundings, then biconvex lens acts as a _________________.

converging lens

Question. In the visible spectrum, red light is at the long wavelength end (~700 nm) while the _________________ is at the short wavelength end (~400 nm).

violet light

Question. When we apply the sign convention, we see that, for erect and virtual image formed by a convex or concave lens, m is _________________.

positive

Question. At the minimum deviation, the refraction ray inside the prism becomes parallel to the _________________.

base

Question. The largest telescope in India is in Kavalur, Tamil Nadu. It is a _________________ diameter reflecting telescope (cassegrain).

2.34 m

Question. A lens of power of –4.0 D means a concave lens of focal length _________________ cm.

–25 cm

Question. For the same angle of incidence, the angles of refraction in three different medium A, B and C are 15°, 25° and 35° respectively. In medium _________________ velocity of light will be minimum.

A

Question. The power of a lens is defined as the _________________ of the angle by which it converges or diverges a beam of light falling at unit distant from the optical centre.

tangent

Question. The angle between the emergent ray and the direction of the incident ray is called the _________________.