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CBSE CLASS XII

Wave Optics

Q.1) A plane wavefront is incident normally on a convex lens. Sketch the refracted wavefront. ( 1 mark )

(Q.2) What happens to frequency when light travels from one medium to another medium? ( 1 mark )

(Q.3) What happens to the wavelength when light travels from rarer medium to denser medium? ( 1 mark )

(Q.4) What is the phase difference between any two points on a wavefront? ( 1 mark )

(Q.5) The refractive index of a medium is . What is the angle of refraction, if the unpolarised light is incident on it at the polarising angle of the medium? (H) ( 1 mark )

(Q.6) What is the value of refractive indices of a medium polarising along 600? ( 1 mark )

(Q.7) What is a polaroid? ( 1 mark )

(Q.8) Define the limit of resolution of a telescope? ( 1 mark )

(Q.9) Give two uses of polaroid. ( 1 mark )

(Q.10) What evidence is there to show that sound is not electromagnetic in nature? ( 1 mark )

(Q.11) To demonstrate the the phenomenon of interference , we require two two sources, which emits radiations (H) (1mark)

(a) of nearly same frequency
(b) of same frequency
(c) of different wavelengths
(d) of the same frequency and having a definite phase relationship

(Q.12) What happens to the fringe pattern when the Young’s double slit experiment is performed in water instead of air? (1mark )

(a) Shrinks
(b) Disappears
(c) Unchanged
(d) Enlarged

(Q.13) In Young’s double slit experiment, the 7th maximum with wavelength 1, is at a distance d1and that with wavelength 2 is at distance then = d₁ / d₂ (H) ( 1 mark )

(Q.14) In a two-slit experiment with white light, a white fringe is observed on a screen kept behind the slits. When the screen is moved by 0.05m, the white fringe ( 1 mark )

(a) does not move at all
(b) gets displaced from its earlier position
(c) becomes coloured
(d) disappears

(Q.15) The frequency of e-m wave which is best suited to observe a particle of radii 3×10^–4 cm is of the order of ( 1 mark )

(a) 10¹⁵
(b) 10¹³
(c) 10¹⁴
(d) 10¹²

(Q.16) The critical angle of light passing from glass to air is minimum for ( 1 mark )

(a) red
(b) green
(c) yellow
(d) violet

(Q.17) The branch of optics dealing with the formation of images using the concept of straight line propagation of light is called: (H) ( 1 mark )

(a) Corpuscular optics
(b) Physical optics
(c) Geometrical optics
(d) Quantum optics

(Q.18) The least distance of distinct vision is ( 1 mark )

(a) d = 25 cm
(b) d = 25 m
(c) d = 15 cm
(d) d = 15 m

(Q.19) The line along which the light travels and the plane of polarisation are inclined to each other at: (H) ( 1 mark )

(Q.20) A parallel beam of monochromatic light of wavelength 5000Å is incident normally on a single narrow slit of width 0.001 mm. The light is focussed by a convex lens on a screen placed on focal plane. The first minimum will be formed for the angle of diffraction equal to(H) ( 1 mark )

(a) 0⁰
(b) 15⁰
(c) 30⁰
(d) 50⁰

(Q.21) A thin transparent sheet is placed in front of a Young's double slit experiment. The fringe width will ( 1 mark )

(a) Increase
(b) Decrease
(c) Remain the same
(d) Become non-uniform

(Q.22) The angle between the reflected and refracted rays at polarising angle is ( 1 mark )

(a) 90⁰
(b) 60⁰
(c) 45⁰
(d) 180⁰

(Q.23) When a beam of light is used to determine the position of an object, the maximum accuracy is achieved if the light is (1 mark )

(a) Polarised
(b) of longer wavelength
(c) of shorter wavelength
(d) of high intensity

(Q.24) A double slit of separation 0.5 mm is illuminated by blue light. The fringes observed at a distance of 1m are 1 mm apart. The wavelength of light will be (H) (1 mark )

(a) 100Å
(b) 500Å
(c) 300Å
(d) 900Å

(Q.25) When a polaroid is rotated, the intensity of light varies but never reduces to zero. It shows that the incident light is (1mark )

(a) completely plane polarized
(b) partially plane polarised
(c) unpolarised
(d) circularly polarised.

(Q.26) The intensity of light emerging from the two slits in Young’s experiment is in the ratio 1:4. The intensity of the minimum to the consecutive maximum will be in the ratio of (1 mark )

(a) 1 : 2
(b) 1 : 4
(c) 1 : 9
(d) 1 : 16

(Q.27) Instead of using two slits as in Young’s experiment, if we use two separate but identical sodium lamps, which of the following will occur? ( 1 mark )

(a) General illumination
(b) Widely separated interferences
(c) Very bright maximum
(d) Very dark minimum

(Q.28) Band spectrum is also called as ( 1 mark )

(a) molecular spectrum
(b) atomic spectrum
(c) flash spectrum
(d) line absorption

(Q.29) The interference fringes formed by a thin oil film on water, when seen in the yellow light of sodium lamp will be: (1mark )

(a) yellow and black
(b) green and red
(c) white
(d) violet and indigo

(Q.30) During the interference of light, energy is ( 1 mark )

(a) created at the maxima
(b) destroyed at the minima
(c) not conserved
(d) redistributed

(Q.31) What should be the order of thickness of oil film on the water surface to enable one see the colours in it? ( 1 mark )

(a) 1 mm
(b) 1 µm
(c) 1Km
(d) 1 cm

(Q.32) In the interference patterns produced by two identical slits.what is the intensity of light at the same spot, if one of the slits is closed? (H) ( 1 mark )

(a) I
(b) I/2
(c) I/4
(d) I/8

(Q.33) Huygen’s wave theory of light cannot explain( 1 mark )

(a) Diffraction
(b) Interference
(c) Polarisation
(d) Photoelectric effect

(Q.34) In Young’s experiment, two coherent sources are placed 0.90 mm apart and the fringes are observed one meter away. If it produces the second dark fringe at a distance of 1mm from the central fringe, the wavelength of the monochromatic light used would be(H) ( 1 mark )

(a) 60 x 10^-4 m
(b) 10 x 10^-4m
(c)10 x 10^-5
(d) 6 x 10^-5

(Q.35) Blue color of the sky is due to the phenomena of ( 1 mark )

(a) Reflection
(b) Refraction
(c) Scattering
(d) Dispersion

(Q.36) Assume that light of wavelength 5x10-6 cm is coming from a star. What is the limit of resolution of a telescope whose objective has a diameter of 100 cm? (H) ( 1 mark )

(a) 3.05 x 10^-6
(b) 1.2 x 10^-6
(c) 3.05 x 10^-8
(d) 2.4 x 10^-8

(Q.37) For what distance is ray optics a good approximation when the aperture is 5 mm wide and wavelength is 100 nm? (1mark )

(a) 20 m
(b) 30 m
(c) 25 m
(d) 40 m

(Q.38) The distance between objective and eye lens of telescope in normal adjustment is (H) ( 1 mark )

(a) x = f₀ + f_e
(b) x = f_{0 x} f_e
(c) x = f₀ - f_e
(d) x = f₀ / f_e

(Q.39) what is the phase difference between any two points on a wave front? ( 1 mark )

(Q.41) What are coherent sources of light? Draw the variation of intensity with position in the Young’s double slit experiment. ( 2 Marks )

(Q.42) In a single slit diffraction experiment, if the width of slit is doubled, how does the

(i) intensity of light and
(ii) width of the central maximum change? Give reason for your answer. ( 2 Marks )

(Q.43) How can one distinguish between an unpolarized light beam and a linearly polarized beam using a polaroid? (H) ( 2 Marks )

(Q.44) Draw a diffraction pattern due to a single slit illuminated by a monochromatic source of light. Light of wavelength 500 nm falls, from a distance source, on a slit 0.50 mm wide. Find the distance between the two dark bands, on either side of the central bright band of the diffraction pattern observed, on a screen placed 2 m from the slit. (H) (3Marks )

(Q.45) State the conditions for obtaining sustained interference of light from different sources. The ratio of intensities of maxima and minima in an interference pattern is found to be 25 : 9. Calculate the ratio of light intensities of the sources producing this pattern. (3Marks )

(Q.46) Define critical angle with reference to the total internal reflection. Calculate the critical angle for glass-air surface, if a ray of light which is incident on the glass surface is deviated through 15⁰, when angle of incidence is 45⁰. (H) ( 3 Marks )

(Q.47) In a single slit diffraction pattern, how does the angular width of central maximum change, when:-

(a) The slit width is decreased.
(b) Distance between the slit and screen is increased.
(c) Light of smaller visible wavelength is used?
Justify your answer in each case. ( 3 Marks )

Q.48) Following figure shows an experimental set up similar to Young’s double slit experiment to observe interference of light. (H)

Here SS₂-SS₁= , write the condition of (i) Constructive (ii) Destructive, interference at any point P is in terms of path difference.

Does the central fringe observed in the above set up lie above or below O? Give reason in support of your answer.

(Q.49) What is meant by interference of light? What are two types of interference? In a double slit experiment with monochromatic light, fringes are observed on a screen placed at some distance from the slits. If the screen is moved by 5x10^-2 m towards the slits, the change in fringe width is 3x10^-5 m. If the distance between the slits is 10^-3 m, calculate the wavelength of light used

Submitted By Mr. Ajay Sharma
Email Id : [email protected]