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Objective Type Question On Class 12 Physics Chapter 9 Ray Optics and Optical Instruments

(1) A concave mirror of focal length f produces an image n times the size of the object. If the image is real then the distance of the object is:
[A] (n – 1) f
[B] (n + 1) f
[C]
[D]
Answer: C
(2) The angle of minimum deviation for an equilateral glass prism is 30°. Refractive index of the prism is:
[A] 1/√3
[B] √2
[C] 1
[D] can’t be determined
Answer: √2

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(3) Light year is the unit of:
[A] distance
[B] time
[C] intensity of light
[D] None of these
Answer: distance
(4) A beam of light is incident at 60° to a plane surface. The reflected and refracted rays are perpendicular to each other. What is the R.I. of the surface:
[A] 1/√3
[B] √3
[C] 1/3
[D] 3
Answer: √3
(5) A ray of light travelling in air is incident of a glass slab. The ray gets partly reflected and partly refracted. The phase difference between the reflected and the refracted waves is :
[A] π/2
[B] π/4
[C] π
[D] zero
Answer: π
(6) Which of-the following is not a property of light?
[A] It can travel through vacuum
[B] It has a finite speed
[C] It requires a material medium for its propagation
[D] It involve transportation energy
Answer: It requires a material medium for its propagation
(7) On reflection from a denser medium, a light wave suffers a phase difference of:
[A] π
[B] π/2
[C] π/4
[D] 2π
Answer: π
(8) Radio waves from an antenna travel with the velocity of:
[A] light
[B] sound
[C] ultrasonics
[D] supersonics
Answer: light
(9) The phase difference between the electric and the magnetic field vectors in electromagnetic waves is
[A] π/4
[B] π/2
[C] π
[D] zero
Answer: zero
(10) Refractive index of water and glass are 4/3 and 5/3. A light ray is going to water from glass. Then, its critical angle will be:
[A]
[B]
[C]
[D]
Answer: B
(11) A telescope has an objective lens of 10 cm diameter and is situated at a distance of 1 km from two objects. The minimum distance between these two objects, which can be resolved by the telescope, when seen in the light of mean λ = 5000 A is of the order of:
[A] 5 mm
[B] 5 cm
[C] 0.5 m
[D] 5 m
Answer: 5 mm
(12) Which of the following is not essential for the formation of a pure spectrum?
[A] parallel beam of light
[B] narrow beam of light
[C] screen
[D] prism in the minimum deviation position
Answer: screen
(13) A convex lens is dipped in a liquid, whose R.I. is equal to that of R.I. of material of the lens. Then its focal length will:
[A] become zero
[B] become infinite
[C] reduce
[D] increase
Answer: become infinite
(14) A certain far-sighted person cannot see objects closer to the eye than 100 cm. The power of the lens which will enable him to read at a distance of 25 cm will be?
[A] 3D
[B] 1D
[C] 4D
[D] 2D
Answer: 3D
(15) Two thin lenses of focal lengths 20 cm and 25 cm are placed in contact. The effective power of the combination is:
[A] 45 D
[B] 9 D
[C] 19 D
[D] 6 D
Answer: 9 D
(16) A double convex air bubble in water behaves as:
[A] Convergent lens
[B] divergent lens
[C] plane slab
[D] concave mirror
Answer: divergent lens
(17) Which produces additional luminiscence in a fluorescent tube?
[A] infra red rays
[B] ultraviolet rays
[C] micro waves
[D] radio waves
Answer: ultraviolet rays
(18) The velocity of light in vacuum is 3 × 1010 cms-1. The velocity of light in a medium (µ = 1.5) is :
[A] 2 × 1010cms-1
[B] 4.5 × 1010cms-1
[C] 1.5 × 1010cms-1
[D] None of these
Answer: 2 × 1010cms-1
(19) When a beam of light is used to determine the position of an object, the maximum accuracy is achieved if the light is :
[A] polarized
[B] of longer λ
[C] of shorter λ
[D] of high intensity
Answer: of shorter λ
(20) The RI. of the material of a prism is √2 and its refracting angle is 30°. One of the refracting surface of the prism is made a mirror. A beam of monochromatic light entering the prism from the other face retraces its path, after reflection from mirror surface. The angle of incidence on prism is:
[A] 0°
[B] 30°
[C] 45°
[D] 60°
Answer: 45°

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