Wave Optics Questions and Answers

In YDSE arrangement shown in figure fringes are seen on screen using monochromatic source Shaving wavelength 3000A in air S and S are two slits separated by d 1mm from each other and D Im Left of slits S and S medium of refractive index 2 is present to the right of slits S and S 13 medium of refractive index is present A thin slab of thickness is placed in front of S The refractive index of slab varies with distance x from its starting face as shown in figure D im Lun d 2 D 1m H Screen h In order to get central maxima at the centre of the screen O the thickness of slab required is B Tum 0 5mm

1 90 2 89 3 67 4 81 In a young s double slit experimental arrangement shown here if a mica sheet of thickness t and refractive index u is placed in front of the slit S then the path difference S P S P is S S I Slit 1 Decreases by 1 t 2 Increases by 1 t 3 Does not change 4 Increases by ut Screen 1 90 36 YDSE 3 67 afgen voit tat S P SP 2 89 fats S 1 1 2 1 t 3 fe 4 ut 1 S S Slit DTS Diemend Test Serical for NEET 2020 Screen 4 81 H a

Objective NCERT Phys 7 Unpolarised light of intensity 32 W m passes through three polarisers such that transmission an of first is crossed with third If intensity of emerge light is 2 W m what is the angle of transmisi axis between the first two polarisers a 30 b 45 c 22 5 4 We Opeics 44 Unpolari The angle rays are tan

E 2 85 The angle between pass axis of polarizer and analyser is 45 The percentage of polarized light passing through analyser is a 75 b 25 c 50 d 100 86 A transparent thin plate of a polaroid is placed on

in water incidence is c 53 74 97 When the angle of incidence is 60 on the surface of a glass slab it is found that the reflected ray is completely polarized The velocity of light in glass is b 50 d 63 c 20 100 An op b c d

7 3 5 2nd 2D 33 In Young s double slit experiment the 10 maximum of wavelength A is at a distance y from its cented maximum and the 5th maximum of wavelength at a distance y from its central maximum The rate Y ly will be 22 a 2 2 c 2 2 34 A narrow slit of width 2 mm is illumin b 2 2 C

slit 27 When the diffraction pattern from a certain illuminated with laser 2 6330 is projected on a screen 150 cm from the slit the second minima on each side are separated by 8 cm This tells us that 06 N The slit is approximately 0 005 cm wide 2 The slit is approximately 0 05 cm wide 3 a 2 is approximately 0 75 a is the slit width 4 a 2 is approximately 750 B A 2

Two In coherent point sources of light SA SB of same power are placed at the level of the slits and S as shown Take D d An interference pattern is observed on the screen If the sources emit monochromatic light of the same wavelength A what fraction of total intensity observed at a point P OP AD d on the screen is due to source SB Take d 2XD Point O lies at the middle level of slits SA S 2 S d S Screen P 5AD 4d

If the first minima in a young s slit experiment occurs directly in front of one of the slits then the wavelength of the radiation used is assume d D Question Type Single Correct Type 1 2 3 4 D d 2D d 4D d

26 A Qubit can be Implemented by Select all that apply a photoionization of photon b polarization of photon c the energy level of the neutron d the Energy level of an atom e rotation of an electron f spin orientation of an electron

39 180 In Young s double slit experiment intensity on the is What will b screen where path difference is 6 intensity at the point where path difference is 1 3 Intensity due to both the sources are same 31 alm 3

A parallel beam of light of wavelength 600 nm is incident normally on a slit of width d If the distance between the slits and the screen is 0 8 m and the distance of 2nd order maximum from the centre of the screen is 15 mm The width of the slit is b 80 m d 200 m a 40 m c 160 m

iv In a Young s double slit experiment the slit separation is doubled To maintain the same fringe spacing on the screen the screen to slit distance D must be changed to a D 2 c D 2 d 2D b D 2

2 2 27 34 A narrow slit of width 2 mm is illuminated by monochromatic light of wavelength 500 nm The distance between the first minima on either side on a screen at a distance of 1 m is a 5 mm c 1 mm 2 b 0 5 mm d 10 mm

A thin layer of colorless oil is spread over water in a container u 1 4 If the light of wavelength 640 nm is absent in the reflected light what is the minimum thickness of oil layer O 179 6 nm O 198 3 nm O 207 6 nm 214 3 nm 3 points

using the 23 In Young s double slit experiment monochromatic light of wavelengths intensity of light at a point on the screen with path difference is M units The intensity of light at a point where path difference is 2 3 is M M M a b c 2 8 d M 16

c 2 and 3 only d 1 and 3 only 2 In Young s double slit experiment two disturbances arriving at a point P have phase difference of The intensity of this point expressed as a fraction of maximum intensity I is d 23 In Young s double slit experiment using

Two polaroids are oriented with their planes perpendicular to incident light and transmission axis making an angle of 37 with each other The percentage of incident unpolarise light transmitted through two polaroids is O 32 O 64 18

45 Match the corresponding entries of column 1 with column 2 Where m is the magnification produced by the mirror 2016 Column 1 A m 2 B C m m 2 1 2 1 D m 2 Column 2 a Convex mirror b Concave mirror c Real image d Virtual image

In the far field diffraction pattern of a single slit under polychromatic illumination the first minimum with the wavelength A is found to be coincide with the third maximum So Question Type Single Correct Type 1 3 0 3 2 2 3 3 3 5x2

In Fraunhofer diffraction by a single slit a position where first order minima is formed by wavelength of 750 nm first order maxima is forme by unknown wavelength The unknown wavelength is 450 nm 500 nm 550 nm 600 nm

Initially interference is observed by YDSE with entire experimental set up inside a chamber filled with air Now chamber is evacuated With same source of light used a careful observer will find that O The fringe width has slightly decreased O Interference pattern is almost absent as it is very much diffused The fringe width has slightly increased There is no change in interference pattern

A concave mirror of small aperture and focal length of 8 cm lies on table and an object is kept vertical above it If concave mirror is filled with water negligible height of refractive index image and object LL coincides The distance of object from mirror is O 12 cm 14 cm 16 cm 18 cm

4 In Young s double slit experiment the distance between slits and screen is 2 m and distance between slits is 0 25 mm A light of wavelength 800 nm is used to find fringes on the screen If screen moves with a speed of 5 m s then first maxima will move with a speed of a 16 mm s b 8 mm s c 20 m s d 50 mm s

The aperture of the largest telescope in the world is 5 m if the separation between the moon and the earth is 4 x 105 km and the wavelength of the visible light is 5000 then the minimum separation between objects on the surface of the moon which can be just resolve is approximately 1 1 m 3 50 m 2 10 m 4 200 m

point Two coherent radio frequency sources separated by 2 0 m are radiating in phase with 1 0m A detector move in a circular path of large radius around the two sources in a plane containing them The number of maximum detected by the detector is Question Type Single Correct Type 18 2 10 3 12

Consider an YDSE that has different slits width as a result amplitudes of waves from two slits are A and 2A respectively If lo be the maximum intensity of the interference pattern then intensity of the pattern at a point where phase difference between waves is is Question Type Single Correct Type 1 locos p 2 sin 3 5 4 cos 4

herent sources are placed at a distance 32 from each other symmetric to the centre of the circle shown in the figure then number of maxima shown on the screen placed along the circumference is 1 16 2 12 321 S S 3 8 PRE MED 4 4 19

4 A plane electromagnetic wave travels in vacuum along z direction If the frequency of the wave is 40 MHz then its wavelength is a 5m b 7 5 m c 8 5 m d 10 m

A monochormatic plane wave of speed c and wavelength is diffracted at a small aperture The diagram illustrates successive wavefronts After what time will some portion of the wavefront XY reach P 3 X Y 22 P 32 42

A point source S of light is fixed on a vertical wall and plane mirror starts moving with a velocity v towards the wall The adjoining figure shows the top view of the situation Now choose the correct option s A Velocity of light spot formed on the wall is i B Light spot is at rest C size of the light spot would increase D size of the light spot would remains same wall d X

The beams A and B of plane polarized light with mutually perpendicular planes of polarization are seen through a polaroid From the position when the beam A has maximum intensity and beam B has zero intensity a rotation of polaroid through 30 makes the two beams appear equally bright If the initial intensities of the two beams are IA and IA IB respectively then equals

c 1 67 13 A monochromatic beam of light falls on apparatus at some angle say 0 as shown in figure A thin sheet of glass is inserted in front of the lower slit S2 The central bright fringe path difference 0 will be obtained a at O b above O c below O S1 0 S2 O

21 Find the maximum intensity in case of interference of infinite identical coherent sources having intensities Io 10 10 10 10 upto infinite 4 16 64 256 a lo c 4 10 b 2 0 d 8 lo

12 Young s double slit experiment is made in a liquid The 10th bright fringe in liquid lies where 6th dark fringe lies in vacuum The refractive index of the liquid is approximately a 1 8 c 1 67 X6 1 5 d 1 2

The intensity of the central fringe obtained in the interference pattern due to two indentical slit sources is I When one of the slits is closed then the intensity at the same point is I Then the correct relation between I and I is ar 1 I L 2 1 21 3 I 41 4 1 1 4

E Initially interference is observed by YDSE with entire experimental set up inside a chamber filled with air Now chamber is evacuated With same source of light used a careful observer will find that The fringe width has slightly decreased Interference pattern is almost absent as it is very much diffused The fringe width has slightly increased There is no change in interference pattern

A screen is placed 2 m from a single slit of width 0 2 mm which is illuminated with 580 nm light a Find the position of the third order dark fringes b What is the width of the central bright fringe

The figure shows Fraunhoffer s diffraction due to a single slit If first minimum is obtained in the direction shown then the path difference between rays 1 and 3 is A 0 C 2 2 1 2 A B 1 3 B 2 4 D

In the figure the intensity of waves arriving at D from two coherent sources S and S is l The wavelength of the wave is Resultant intensity at D will be 4m 4m 1 41 3 21 S 3m S 2 L 4 Zero

39 Figure given below shows four progressive waves 42 A B C and D with their phase expressed with respect to the wave A It can be calculated from the figure that 3 2 20 fot 1 The wave C is ahead by a phase angle of 1 2 and the wave B lags behind by a phase angle of n 2 2 The wave C lags behind by a phase angle of 1 2 and the wave B is ahead by a phase angle of n 2 3 The wave C is ahead by a phase angle of x and the wave B lags behind by a phase angle of n 4 The wave C lags behind by a phase angle of it and the wave B is ahead by a phase angle of r 40 Velocity of sound waves in air is 330 m s For 43 44

waves in air 36 For the wave shown in figure given below th frequency and wavelength if its speed 320 m sec are ma A 1 8 cm 400 Hz 2 80 cm 40 Hz 3 8 cm 4000 Hz 4 40 cm 8000 Hz x 20 cm

In YDSE set up one of the slit S of a double slit system is wider than the other so that the amplitude of light reaching the central part of the screen from one slit acting alone is twice that from the other slit acting alone If d 4A maximum value of sine so that intensity at point P is equal to average intensity on screen is of d S S Correct answer 05 N 6 Find the value 16

Visible light of wavelength 6000 x 10 8 cm falls normally on a single slit and produces a diffraction pattern It is found that the second diffraction minimum is at 60 from the central maximum If the first minimum is produced at 0 then 0 is close to 1 20 2 45 3 30 4 25

The light beams of intensities in the ratio of 9 1 are allowed to interfere What will be the ratio of intensities of maxima and minima A B skipped 3 1 4 1

Questions 15 to 17 are based on the following write up If Snell s law is found valid for two mediums whose refractive indices have opposite signs the incident and the refracted rays must remain on the same side of the normal at the point of incidence In the figure is shown a ray crossing the interface between two mediums I and II The ray makes angles and 0 with normal in the medium I and II The refractive indices of the mediums 1 and 2 have opposite signs Snell s law is expressed for the above situation as usual by the equation sint sin 0 Therefore to satisfy this equation the angles and must also have opposite signs 5 A self luminous point object placed at a distance x from a slab of transparent material of negative refractive index is viewed through the slab as shown in the figure Thickness of the slab is d refractive index of material of the slab with respect to the outside medium is 1 For different moduli of values of x and d the observer may find real or virtual image of the object Which of the following statements is true a If x d image is virtual and for x d image is real b If x d image is virtual and for x d image is real c If x d image is virtual and for x d image is real d If x d image is virtual and for x d image is real Object 16 Suppose a virtual object instead of a real object is at a distance x from the surface A of the slab Now which of the following statements is true a For the cases x d and x da real and erect image is formed outside the slab b For the cases x d and x d a real and inverted image is formed outside the slab virtual e If x d a real image is formed outside the slab and for x d a image is formed inside the slab d If x d a real image is formed and for x d a virtual image is formed in both the cases the image is outside the slab A 0 Medium Slab 0

11 While travelling by a train or by a bus if we look outside we observe some effects These effects and some facts possibly explaining these effects are given in the first and the second columns of the following table Suggest suitable matches Column I Column II a Nearby objects appear moving p Human eye senses the direction past faster than distant objects from which light enters it b Extremely distant objects appe q It cannot resolve two points if ar moving along with us they subtend an angle less than one minute r Persistence of eye is 0 1 s

Bodies that can be impregnated with water colours of their surface appear richer after moistening Which of the following is the most appropriate reason for this effect a Due to moistening surface irregularities are covered with water film which reduces diffused reflection of light b Due to moistening surface irregularities are covered with water film which reduces amount of reflected light c Due to moistening surface irregularities are covered with water film which increases amount of reflected light

When the Sun is behind dark clouds and there are gaps in the clouds you will often see sunlight fanning out from the gaps as shown in the given photograph Though the rays are closely parallel but we see them diverging as they approach the earth Which of the following statements most suitably explains this effect a Distant objects appear smaller than nearer objects b Sunrays are actually radiated from the sun radially c Light bends at sharp corners of opaque object that it encounters d The gaps work as light sources at finite distance hence radiate diverging light

5 A beam of light coming from a rarer medium is partially reflected from the surface of a denser medium and partially refracted into the denser medium If the reflected and the refracted rays are perpendicular to each other and the ratio of the refractive indices of the denser and rarer medium is 3 the angle of refraction will be 1 60 2 30 3 45 4 41 5