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

Please refer to the MCQ Questions for Class 12 Physics Chapter 9 Ray Optics and Optical Instruments with Answers. The following Ray Optics and Optical Instruments Class 12 Physics MCQ Questions have been designed based on the latest syllabus and examination pattern for Class 12. Our experts have designed MCQ Questions for Class 12 Physics with Answers for all chapters in your NCERT Class 12 Physics book.

## Ray Optics and Optical Instruments Class 12 MCQ Questions with Answers

See below Ray Optics and Optical Instruments Class 12 Physics MCQ Questions, solve the questions and compare your answers with the solutions provided below.

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.

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

A

Question. A converging beam of rays is incident on a diverging lens. Having passed through the lens the rays intersect at a point 15 cm from the lens on the opposite side. If the lens is removed, the point where the rays meet will move 5 cm closer to the lens. The focal length of the lens is
(a) 5 cm
(b) –10 cm
(c) 20 cm
(d) –30 cm

D

Question. A beam of light composed of red and green ray is incident obliquely at a point on the face of rectangular glass slab. When coming out on the opposite parallel face, the red and green ray emerge from
(a) two points propagating in two different non parallel directions
(b) two points propagating in two different parallel directions
(c) one point propagating in two different directions
(d) one point propagating in the same directions.

B

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

B

Question. A bubble in glass slab (m = 1.5) when viewed from one side appears at 5 cm and 2 cm from other side, then thickness of slab is
(a) 3.75 cm
(b) 3 cm
(c) 10.5 cm
(d) 2.5 cm

C

Question. A lens having focal length f and aperture of diameter d forms an image of intensity I. Aperture of diameter d/2 in central region of lens is covered by a black paper. Focal length of lens and intensity of image now will be respectively
(a) f and I/4
(b) 3f/4 and I/2
(c) f and 3I/4
(d f/2 and I/2

C

Question. A boy is trying to start a fire by focusing sunlight on a piece of paper using an equiconvex lens of focal length 10 cm. The diameter of the sun is 1.39 × 109 m and its mean distance from the earth is 1.5 × 1011 m. What is the diameter of the sun’s image on the paper?
(a) 6.5 × 10–5 m
(b) 12.4 × 10–4 m
(c) 9.2 × 10–4 m
(d) 6.5 × 10–4 m

C

Question. For the angle of minimum deviation of a prism to be equal to its refracting angle, the prism must be made of a material whose refractive index
(a) lies between √2 and 1
(b) lies between 2 and √2
(c) is less than 1
(d) is greater than 2

B

Question. Light travels through a glass plate of thickness t and having refractive index m. If c be the velocity of light in vacuum, the time taken by the light to travel this thickness of glass is
(a) t/μc
(b) tμc
(c) μ1/c
(d) tc/μ

C

Question. An electric bulb illuminates a plane surface. The intensity of illumination on the surface at a point 2 m away from the bulb is 5 × 10–4 phot (lumen/cm2). The line joining the bulb to the point makes an angle of 60º with the normal to the surface. The luminous intensity of the bulb in candela (candle power) is
(a) 40 √3
(b) 40
(c) 20
(d) 40 × 10–4

B

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°

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

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°

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

B

Question. If two mirrors are kept at 60º to each other, then the number of images formed by them is
(a) 5
(b) 6
(c) 7
(d) 8

A

Question. A convex mirror of focal length f produces an image (1/n)th of the size of the object. The distance of the object from the mirror is
(a) (n – 1) f
(b) f/n
(c) (n + 1) f
(d) nf

A

Question. In a room containing smoke particles, the intensity due to a source of light will
(a) obey the inverse square law
(b) be constant at all distances
(c) increase with distance from the source than the inverse fourth power law
(d) fall faster with distance from the source than the inverse fourth power law

D

Question. Amount of light entering into the camera depends upon.
(a) focal length of objective lens
(b) product of focal length and diameter of the objective lens
(c) distance of object from camera
(d) aperture setting of the camera

D

Question. An achromatic convergent doublet of two lenses in contact has a power of + 2D. The convex lens has power + 5D. What is the ratio of dispersive powers of convergent and divergent lenses ?
(a) 2 : 5
(b) 3 : 5
(c) 5 : 2
(d) 5 : 3

B

Question. A man wants to see two poles, separately, situated at 11 km. The minimum distance (approximately) between these poles will be
(a) 5 m
(b) 0.5 m
(c) 1 m
(d) 3 m

D

Question. The dispersive power of material of a lens of focal length 20 cm is 0.08. What is the longitudinal chromatic aberration of the lens ?
(a) 0.08 cm
(b) 0.08/20 cm
(c) 1.6 cm
(d) 0.16 cm

C

Question. Wavelength of light used in an optical instrument are λ1 = 4000Å and λ2 = 5000 Å, then ratio of their respective resolving powers (corresponding to λ1 and λ2) is
(a) 16 : 25
(b) 9 : 1
(c) 4 : 5
(d) 5 : 4

D

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

A

Question. In optical fibres, propagation of light is due to
(a) diffraction
(b) total internal reflection
(c) reflection
(d) refraction

B

Question. What causes chromatic aberration?
(a) Non – paraxial rays
(b) Paraxial rays
(c) Variation of focal length with colour
(d) Difference in radii of curvature of the bounding surfaces of the lens

C

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 pond
(c) Mirage on hot summer days
(d) Brilliance of diamond

B

Question. Two similar thin equi-convex lenses, of focal length f each, are kept coaxially in contact with each other such that the focal length of the combination is F1.
When the space between the two lenses is filled with glycerin (which has the same refractive index (m = 1.5) as that of glass) then the equivalent focal length is F2. The ratio F1 : F2   will be
(a) 3 : 4
(b) 2 : 1
(c) 1 : 2
(d) 2 : 3

C

Question. An equiconvex lens has power P. It is cut into two symmetrical halves by a plane containing the principal axis. The power of one part will be
(a) 0
(b) P/2
(c) P/4
(d) P

D

Question. The speed of light in media M1 and M2 are 1.5 × 108 m/s and 2.0 × 108 m/s respectively. A ray of light enters from medium M1 to M2 at an incidence angle i. If the ray suffers total internal reflection, the value of i is
(a) equal to sin-1 (2/3)
(b) equal to or less than sin-1 (3/5)
(c) equal to or greater than sin−1 (3/4)

C

Question. Optical fibre are based on
(a) total internal reflection
(b) less scattering
(c) refraction
(d) less absorption coefficient.

A

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

B

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
(a) 18 cm
(b) 24 cm
(c) 30 cm
(d) 40 cm

B

Question. Light enters at an angle of incidence in a transparent rod of refractive index n. For what value of the refractive index of the material of the rod, the light once entered into it will not leave it through its lateral face whatsoever be the value of angle of incidence?
(a) n = 1.1
(b) n = 1
(c) n > 2
(d) n = 1.3

C

Question. A beam of light from a source L is incident normally on a plane mirror fixed at a certain distance x from the source. The beam is reflected back as a spot on a scale placed just above the source L. When the mirror is rotated through a small angle q, the spot of the light is found to move through a distance y on the scale. The angle q is given by
(a) y/x
(b) x/2y
(c) x/y
(d) y/2x

D

Question. An object is placed at a distance 2f from the pole of a convex mirror of focal length f. The linear magnification is
(a) 1/3
(b) 2/3
(c) 3/4
(d) 1

A

Question. Two plane mirrors are inclined at 70°. A ray incident on one mirror at angle, q after reflection falls on second mirror and is reflected from there parallel to first mirror. The value of q is
(a) 45°
(b) 30°
(c) 55°
(d) 50°

D

Question. When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid, it acts as a plane sheet of glass. This implies that the liquid must have refractive index
(a) equal to that of glass
(b) less than one
(c) greater than that of glass
(d) less than that of glass.

A

Question. A concave mirror of focal length f1 is placed at a distance of d from a convex lens of focal length f2. A beam of light coming from infinity and falling on this convex lens – concave mirror combination returns to infinity. The distance d must equal
(a) f1 + f2
(b) –f1 + f2
(c) 2f1 + f2
(d) –2f1 + f2

C

Question. A biconvex lens has a radius of curvature of magnitude 20 cm. Which one of the following options describe best the image formed of an object of height 2 cm placed 30 cm from the lens?
(a) Virtual, upright, height = 1 cm
(b) Virtual, upright, height = 0.5 cm
(c) Real, inverted, height = 4 cm
(d) Real, inverted, height = 1 cm

C

Question. 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.

D

Question. Two identical glass (mg = 3/2) equiconvex lenses of focal length f each are kept in contact. The space between the two lenses is filled with water (mw = 4/3). The focal length of the combination is
(a) f/3
(b) f
(c) 4f/3
(d) 3f/4

D

Question. A tall man of height 6 feet, want to see his full image.
Then required minimum length of the mirror will be
(a) 12 feet
(b) 3 feet
(c) 6 feet
(d) any length

B

Question. An air bubble in a glass slab with refractive index 1.5 (near normal incidence) is 5 cm deep when viewed from one surface and 3 cm deep when viewed from the opposite face. The thickness (in cm) of the slab is
(a) 8
(b) 10
(c) 12
(d) 16.

C

Question. A plano convex lens fits exactly into a plano concave lens. Their plane surfaces are parallel to each other.
If lenses are made of different materials of refractive indices m1 and m2 and R is the radius of curvature of the curved surface of the lenses, then the focal length of the combination is
(a) R/(μ1-μ2)
(b) 2R/(μ2-μ1)
(c) R/(μ1-μ2)
(d)  R/2(μ1-μ2)

A

Question. A microscope is focussed on a mark on a piece of paper and then a slab of glass of thickness 3 cm and refractive index 1.5 is placed over the mark. How should the microscope be moved to get the mark in focus again?
(a) 2 cm upward
(b) 1 cm upward
(c) 4.5 cm downward
(d) 1 cm downward

B

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

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

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