# Refraction of Light Questions ### Refraction of Light at Plane Surfaces:

Ques: A glass slab of thickness 3 cm and refractive index 3/2 is placed on ink mark on a piece of paper. For a person looking at the mark at a distance 5.0 cm above it, the distance of the mark will appear to be
(a) 3.0 cm
(b) 4.0 cm
(c) 4.5 cm
(d) 5.0 cm

Ans. (b)

Ques. The refractive index of a piece of transparent quartz is the greatest for
(a) Red light
(b) Violet light
(c) Green light
(d) Yellow light

Ans. (b)

Ques: Speed of light is maximum in
(a) Water
(b) Air
(c) Glass
(d) Diamond

Ans. (b)

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Ques: The wavelength of sodium light in air is 5890 Å. The velocity of light in air is 3 x 108 ms–1. The wavelength of light in a glass of refractive index 1.6 would be close to
(a)

5890 Å
(b) 3681 Å
(c) 9424 Å
(d) 15078 Å

Ans. (b)

Ques: An underwater swimmer is at a depth of 12 m below the surface of water.  A bird is at a height of 18 m from the surface of water, directly above his eyes.  For the swimmer the bird appears to be at a distance from the surface of water equal to (Refractive Index of water is 4/3)
(a) 24 m
(b) 12 m
(c) 18 m
(d) 9 m

Ans. (a)

Ques: Velocity of light in a medium is 1.5 x 108 m/s. Its refractive index will be
(a) 8
(b) 6
(c) 4
(d) 2

Ans. (d)

Ques: Ray optics is valid, when characteristic  dimensions are
(a) Of the same order as the wavelength of light
(b) Much smaller than the wavelength of light
(c) Of the order of one millimeter
(d) Much larger than the wavelength of light

Ans. (d)

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Ques: A tank is filled with benzene to a height of 120 mm. The apparent depth of a needle lying at a bottom of the tank is measured by a microscope to be 80 mm.  The refractive index of benzene is
(a) 1.5
(b) 2.5
(c) 3.5
(d) 4.5

Ans. (a)

Ques: A ray of light is incident on a transparent glass slab of refractive index 1.62.  The reflected and the refracted rays are mutually perpendicular. The angle of incidence is
(a) 58.3o
(b) 50o
(c) 35o
(d) 30o

Ans. (a)

Ques: A plane glass slab is kept over various coloured letters, the letter which appears least raised is
(a) Blue
(b) Violet
(c) Green
(d) Red

Ans. (d)

Ques: On heating a liquid, the refractive index generally
(a) Decreases
(b) Increases or decreases depending on the rate of heating
(c) Does not change
(d) Increases

Ans. (a)

Ques: The distance travelled by light in glass (refractive index =1.5)  in a nanosecond will be
(a) 45 cm
(b) 40 cm
(c) 30 cm
(d) 20 cm

Ans. (d)

Ques: When light enters from air to water, then its
(a) Frequency increases and speed decreases
(b) Frequency is same but the wavelength is smaller in water than in air
(c) Frequency is same but the wavelength in water is greater than in air
(d) Frequency decreases and wavelength is smaller in water than in air

Ans. (b)

Ques: Which of the following is not a correct statement
(a) The wavelength of red light is greater than the wavelength of green light
(b) The wavelength of blue light is smaller than the wavelength of orange light
(c) The frequency of green light is greater than the frequency of blue light
(d) The frequency of violet light is greater than the frequency of blue light

Ans. (c)

Ques: A monochromatic beam of light passes from a denser medium into a rarer medium. As a result
(a) Its velocity increases
(b) Its velocity decreases
(c) Its frequency decreases
(d) Its wavelength decreases

Ans. (a)

Ques: Light travels through a glass plate of thickness t and having refractive index n. If c is the velocity of light in vacuum, the time taken by the light to travel this thickness of glass is
(a) t/nc
(b) tnc
(c) nt/c
(d) tc/n

Ans. (c)

Ques: Ray optics fails when
(a) The size of the obstacle is 5 cm
(b) The size of the obstacle is 3 cm
(c) The size of the obstacle is less than the wavelength of light
(d) (a) and (b) both

Ans. (c)

Ques: Light of different colours propagates through air
(a) With the velocity of air
(b) With different velocities
(c) With the velocity of sound
(d) Having the equal velocities

Ans. (d)

Ques: A light wave has a frequency of 4 x 1014 Hz and a wavelength of 5 x 10–7 meters in a medium. The refractive index of the medium is
(a) 1.5
(b) 1.33
(c) 1.0
(d) 0.66

Ans. (a)

Ques: To an observer on the earth the stars appear to twinkle. This can be ascribed to
(a) The fact that stars do not emit light continuously
(b) Frequent absorption of star light by their own atmosphere
(c) Frequent absorption of star light by the earth’s atmosphere
(d) The refractive index fluctuations in the earth’s atmosphere

Ans. (d)

Ques: The ratio of the refractive index of red light to blue light in air is
(a) Less than unity
(b) Equal to unity
(c) Greater than unity
(d) Less as well as greater than unity depending upon the experimental arrangement

Ans. (a)

Ques: Monochromatic light of frequency 5 x 1014 Hz travelling in vacuum enters a medium of refractive index 1.5. Its wavelength in the medium is
(a) 4000 Å
(b) 5000 Å
(c) 6000 Å
(d) 5500 Å

Ans. (a)

Ques. Refractive index for a material for infrared light is
(a) Equal to that of ultraviolet light
(b) Less than for ultraviolet light
(c) Equal to that for red colour of light
(d) Greater than that for ultraviolet light

Ans. (b)

Ques. When a light wave goes from air into water,  the quality that remains unchanged is its
(a) Speed
(b) Amplitude
(c) Frequency
(d) Wavelength

Ans. (c)

Ques. The bottom of a container filled with liquid appear slightly raised because of
(a) Refraction
(b) Interference
(c) Diffraction
(d) Reflection

Ans. (a)