Ray Optics and Optical Instruments

Ray Optics and Optical Instruments Class 12 Physics MCQs

1. For a total internal reflection, which of the following is correct?
(a) Light travels from rarer to denser medium.
(b) Light travels from denser to rarer medium.
(c) Light travels in air only.
(d) Light travels in water only.

2. Critical angle of glass is θ₂ and that of water is θ₂. The critical angle for water and glass surface would be (μ_g = 3/2, μ_w = 4/3).
(a) less than θ₂
(b) between θ₁ and θ₂
(c) greater than θ₂
(d) less than θ₁

3. Mirage is a phenomenon due to
(a) refraction of light
(b) reflection of light
(c) total internal reflection of light
(d) diffraction of light.

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

5. Which of the following forms a virtual and erect image for all positions of the object?
(a) Concave lens
(b) Concave mirror
(d) Convex mirror
(d) Both (a) and (c)

6. Two lenses of focal lengths 20 cm and – 40 cm are held in contact. The image of an object at infinity will be formed by the combination at
(a) 10 cm
(b) 20 cm
(c) 40 cm
(d) infinity

7. Two beams of red and violet color are made to pass separately through a prism (angle of the prism is 60°). In the position of minimum deviation, the angle of refraction will be
(a) 30° for both the colors
(b) greater for the violet color
(c) greater for the red color
(d) equal but not 30° for both the colors

8. Which of the following colours of white light deviated most when passes through a prism?
(a) Red light
(b) Violet light
(c) Yellow light
(d) Both (a) and (b)

9. An under-water swimmer cannot see very clearly even in absolutely clear water because of
(a) absorption of light in water
(b) scattering of light in water
(c) reduction of speed of light in water
(d) change in the focal length of eye lens

10. An astronomical refractive telescope has an objective of focal length 20 m and an eyepiece of focal length 2 cm. Then
(a) the magnification is 1000
(b) the length of the telescope tube is 20.02 m
(c) the image formed of inverted
(d) all of these

11. A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 ’em 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

Question 12.
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

Question 13.
Two points P and q are situated at the same distance from a source of light but on opposite sides. The plane difference between the light waves passing through P and q will be:
(a) n
(b) 2n
(c) \(\frac{π}{2}\)
(d) zero

Question 14.
The phase difference between the electric and the magnetic field vectors in electromagnetic waves is
(a) \(\frac{π}{4}\)
(b) \(\frac{π}{2}\)
(c) π
(d) zero

Question 15.
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) \(\frac{π}{2}\)
(b) \(\frac{π}{4}\)
(c) π
(d) zero

Question 16.
Which of the following cannot be polarised?
(a) radiowaves
(b) transverse waves
(c) sound waves
(d) X-rays

Question 17.
Light year is the unit of:
(a) distance
(b) time
(c) intensity of light
(d) None of these

Question 18.
If a mirror is approaching you at a speed of 10 ms^1, the speed with which your image approach you is:
(a) 10 ms^-1
(b) 5 ms^-1
(c) 20 ms^-1
(d) 15 ms^-1

Question 19.
The refractive indices (R.I.) of glass and water with respect to air are 3/2 and 4/3 respectively. The R.I. of glass w.r. to w ater is:
(a) 8/9
(b) 9/8
(c) 7/6
(d) 2

Question 20.
The angle of minimum deviation for an equilateral glass prism is 30°. Refractive index of the prism is:
(a) \(\frac{1}{√3}\)
(b) √2
(c) 1
(d) can’t be determined

Question 21.
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) \(\frac{1}{√3}\)
(b) √3
(c) \(\frac{1}{3}\)
(d) 3

Question 22.
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) (\(\frac{n+1}{n}\))f
(d) (\(\frac{n-1}{n}\))f

Question 23.
A convergent lens will become less convergent in :
(a) oil
(b) water
(c) both of (a) and (b)
(d) none of these

Question 24.
A thin glass (RI = \(\frac{3}{2}\)) lens has optical power of – 5D in air. Its optical power in a liquid medium with RI = 1.6 will be:
(a) -2.5 D
(b) 25 D
(c) -ID
(d) 0.625 D

Question 25.
On reflection from a denser medium, a light wave suffers a phase difference of:
(a) π
(b) \(\frac{π}{2}\)
(c) \(\frac{π}{4}\)
(d) 2π

Question 26.
The branch of optics dealing with the formation of images using the concept of straight line propagation of light is called:
(a) geometrical optics
(b) physical optics
(c) corpuscular optics
(d) quantum optics

Question 27.
When light travels from one medium to another, which of the following does not change?
(a) frequency
(b) refractive index
(c) velocity
(d) wavelength

Question 28.
Two lens of power -15 D and +5 D are placed in contact co-axially. The focal length of equivalent lens is:
(a) -10 cm
(b) -20 cm
(c) +10 cm
(d) None

Question 29.
Refractive index of water and glass are \(\frac{4}{3}\) and \(\frac{5}{3}\). A light ray is going to water from glass. Then, its critical angle will be:
(a) sin^-1\(\frac{4}{5}\)
(b) sin^-1\(\frac{5}{6}\)
(c) sin^-1\(\frac{1}{2}\)
(d) sin^-1(\(\frac{2}{1}\))

Question 30.
The air bubble inside water shine due to:
(a) Reflection
(b) Refraction
(c) T.l.R.
(d) None of these

Question 31.
When a ray of light (white) enters a lens, undergoes a change is:
(a) wavelength
(b) velocity
(c) frequency
(d) both velocity and wavelength

Question 32.
Radio waves from an antenna travel with the velocity of:
(a) light
(b) sound
(c) ultrasonics
(d) supersonics

Question 33.
A point object is placed at the centre of a glass sphere of radius 6 cm 3 and RI = \(\frac{3}{2}\). The distance of virtual image from the surface of the sphere is :
(a) 2 cm
(b) 4 cm
(c) 6 cm
(d) 12 cm

Question 34.
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°

Question 35.
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

Question 36.
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

Question 37.
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

Question 38.
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

Question 39.
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

Question 40.
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

Question 41.
Which produces additional luminiscence in a fluorescent tube?
(a) infra red rays
(b) ultraviolet rays
(c) micro waves
(d) radio waves

Question 42.
For achromatic combination of lenses, if we use two lenses of focal length f’ and f₁ dipersive power to ω and ω’ respectively, then
(a) ω = ω₀, ω’= 2ω₀, f’ = 2f
(b) ω = ω₀, ω’ = 2ω₀, f’ = -2f
(c) ω = ω₀, ω’ = 2ω₀, f’ = f/2
(d) ω = ω₀, ω’ = 2ω₀, f’ = -f/2

Question 43.
ar point of a myopic eye is 40 cm. The dioptic power of a corrective lens is:
(a) 40 D
(b) -4 D
(c) -2.5 D
(d) -0.25 diopter

Question 44.
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) \(\frac{1}{9}\) D
(d) 6 D

Question 45.
A blue cross on the white background is illuminated with white light and is observed through red filter. What is seen?
(a) A red cross on a black background
(b) A blue cross on a red background
(c) A red cross on a blue background
(d) A black cross on a red background

Question 46.
The angle of deviation for a prism is greatest for:
(a) violet
(b) red
(c) orange
(d) yellow

Question 47.
A double convex air bubble in water behaves as:
(a) Convergent lens
(b) divergent lens
(c) plane slab
(d) concave mirror