Wave Optics Questions and Answers

29 A beam of light of wavelength 6000 A falls on a narrow slit and the diffraction pattern is observed at a screen 3 m away from the slit If the slit width is 0 9 mm then the position of the first order minimum from the central maximum is 1 4 mm 3 1 mm 2 3 mm 4 2 mm

Q 12 White light P Q Dispersion First prism Recombination Second prism R P Light of seven colours R Patch of white light White light White screen S Newton carried out the above experiment to prove one important characteristic of light What is that characteristic and give the reasoning behind his observation 2

2 Interference fringes are produced with monochromatic light falling normally a wedge shaped film of refractive index 1 4 The angle of the wedge is 10 seconds of an arc and th distance between the successive fringes in 0 5 cm Calculate the wavelength of the light used

Three identical sources S S and S3 are placed at the vertices of an equilat intensity Io each at centroid c of triangle The resulting intensity of light at c will be S S A B C D 310 610 zero 910 C S3

SolveLancer Test In diffraction pattern the variation of intensity on the screen is given by 1 b i Most of the diffracted light is distributed between sine and 1 10 sin B bsine The intensity plot with sine indicates that ii Intensity of Ist maximum after central one is only of the intensity of the Test 62 5 central maximum SolveLancer a i true ii false b i ii both true c Only i true d i ii both false

In YDSE one of the slit is wider than other so that amplitude of the light from one slit is double of that from other slit if Im be the maximum intensity the resultant intensity is I when they interfere at a phase difference is given by Question Type Single Correct Type 1 2 m 1 2cos 6 2 3 m 4 5 cos 4 Im 1 4cos 6 2 1 8cos 6 2

22 Suppose an electron microscope uses a beam of electrons accelerated through a 1 V potential a Estimate the resolving power of that microscope b Would it be able to image a 200 nm cell A 4 nm cell membrane A 0 1 nm hydrogen atom

A ray of light of intensity is incident on a parallel glass slab at a point A as shown in the figure It undergoes partial reflection and refraction At each reflection 25 of incident light is reflected The rays AB and A B undergo interference Then yc fzu faa sef uz 1 dz cid 4fc1 42 145 wich Gudda am guada gura i 2 3 2 cl 25 H quafda da z AB A B fazu ge A is C Io 64 B 7 16 afaczu ch ufuga da 10 D The maximum intensity of interference Io B The maximum intensity of interference 49 is Io 64 af Correct Answer 7 16 B Io agu Yg ada 64 Correct Answer 49 Io 64 The minimum intensity of interference is The minimum intensity of interference is

A light beam shines through a thin slit and illuminates a distant screen The central bright fringe on the screen is 1 00 cm wide as measured between the dark fringes that border it on either side Which of the following actions would decrease the width of the central bright fringe There may be more than one correct choice O put the apparatus all under water increase the width of the slit decrease the width of the slit decrease the wavelength of the light increase the wavelength of the light

2 7 Two Polaroids P and P are placed with their axis perpendicular to each other Unpolarised light I is incident on P A third polaroid P is kept in between P and P such that its axis makes an angle 45 with that of P The intensity of transmitted light through 1 2017 Delhi P is 2 a Io Two Io C b I 8 herent sources of intensity ratio a interfere d I 2 16

7 Let S and S be the two slits in Young s double slit experiment If central maxima is observed at P and angle S PS 0 0 is small find the y coordinates of the 3rd minima assuming the origin at the central maxima wavelength of monochromatic light used 21 b a c 0 1010 5 1 0 20 d 2 0

In a Young s double slit experiment the fringes are displaced by a distance x when a glass plate of refractive index 1 5 is introduced in the path of one of the beams Then this plate is replaced by another plate of the same thickness the shift 3 22 x The refractive index of the second plate is of fringes is A 2 25 B 2 0 C 1 75 C

Aa and Am are the wavelengths of a beam of light in air and medium respectively If 0 is the polarising angle the correct relation between a m and 0 is tak A We 3 a 2m cot 0 tan 02 2 tan s 2 4 2 2 cot 0 a m meste

An electric bulb illuminates a plane surface The intensity of illumination on the surface at a point 2 m away from the bulb is 5x 10 phot lumen sq cm The line joining the bulb to the point makes an angle of 60 with the normal to the surface The intensity of the bulb in candela is a 40 3 c 20 b 40 d 40 10 4 IIT 1980

Two coherent sources S and S are placed at a distance 2d from each other and have wavelength d where 3 5 as shown in the figure The number of maximas on screen 1 and 2 respectively are Assume that the screens are placed one by one S 1 7 3 Screen 2 2d D d S Screen 1

What will happen when the light suffers refraction while it travels from a rarer denser medium 1 Its wavelength increases but frequency remains constant 2 Its wavelength decreases but frequency remains constant 3 Its wavelength remain constant but frequency decreases

In Young double slit interference experiment the distance between two sources is 0 1 mm The distance of the screen from the sources is 20 cm Wavelength of light used is 5460 Then the angular position of the first dark fringe is A 0 08 B C 0 16 Correct Answer 0 20 0220

3 0 225 cm 4 0 25 cm In single slit diffraction light of wavelength 5 5000A is used Distance of screen from slit is 3m Distance between 2nd dark and 1st dark fringe is 2 mm The width of the slit is 1 0 20 mm 2 0 75 mm 3 0 50 mm 4 0 10 mm 3 0 225 cm gel fet fad 5000 ff 3 m 1 2 Ay a 1 a 2 mm fcte of after 1 0 20 mm 3 0 50 mm 4 0 25 cm 2 0 75 mm 4 0 10 mm

Two balls at the surface of a pond are moved up and down in phase and at the same frequency They make the interference pattern shown above on the pond as waves travel across the surface The balls are the two sources The yellow point is 232 cm away from the source on the left and the wavelength of the waves produced by each source is 40 cm 3 Question 11a Homework Answered Impor

3 Two slits S and S illuminated by a white light 2 source give a white central maxima A transparent sheet of refractive index 1 25 and thickness t is placed in front of S Another transparent sheet of refractive index 1 50 and thickness t is placed in front of S If central maxima is not affected then the ratio of t t will be 1 1 2 2 2 1 3 1 4 4 4 1 In a Young s double slit experiment let be the 3 3 Trafora renfor s af S qv a date x1 81 1 25 fafts afy 11 50 date 1 effe aft 3fearg unfara at ghan 8 at ETT 1 1 2 3 1 4 in fa faz gn 2 2 1

In a young s double shit interference patter the intensity of the central fringe at P I when one slit width is reduced to one fourth the intensity at P will be A 1 2 C 9 16 I B 1 4 D 3 4 I

A flat mirror revolves at constant angular 6 velocity making 2 rad s with what speed will a light spot move along a spherical screen with a radius of 10 m if the mirror is at the centre of curvature of the screen C 1 20 m s 2 40 m s 3 2 m s 4 none of these 10m Bright spot Spherical screen 1 20 m s 2 40 m s 3 2 m s 4 2 2 C un sent and fare fondoft and 10m Bright spot Spherical screen

Example 3 A rod AB of length 5 cm lies along the principal axis of the concave mirror of focal length 15 cm in such a way that the end closer to the pole is 30 cm away from it Find the length of the image f 15 cm R 2f 30 cm Solution BA A BA 5 cm F 30 cm

Topic SYLLABUS 5 6 In a Young s double slit experiment the slits are 1 2 mm apart and are illuminated with a mixture of two wavelength 750nm and A 900nm The minimum distance from the common central bright fringe on a screen 2m from the slits where a bright fringe from one interference pattern coincides with a bright fringe from the other is 1 1 5 mm 2 3 mm 3 4 5 mm 4 6 mm Two light wave from coherant sources superpose 2 affer 2 mm vaatame 750nm 900mm are for ser fer fan af a cum fet qucficit for you f fer 2m 8 1 1 5 mm 3 4 5 mm 2 3 mm 4 6 mm for A

D When a YDSE is performed using a monochromatic source of light fringe width is found to be 1 2 mm The minimum distance above 3 4 central maxima at which intensity is th of the maximum value is 1 0 1 mm 3 0 3 mm 2 0 2 mm 4 0 4 mm

A microscope is focussed on a point at the base of an empty vessel Now water 3 is poured in it up to a height of 4 cm Next a light oil 2 is placed on water up to a height of 2 cm The oil does not mix with water In this condition by how much should the microscope be raised to focus the particular point 1 67 cm

2 5 5 Two polaroid sheets are placed one over the other with their axes inclined to each other at an angle 8 If only 12 5 of intensity of unpolarised light incident on the first sheet emerges out from the second sheet the value of 0 is 2 90 1 45 3 30 4 60

In the adjacent diagram CP represents wavefront and AO and BP corresponding two rays If one particular condition on maximum e for destructive interference at P between the ray BP and reflected ray OP is cose then n is nd CP af Pfa ef Aga A I 1 P BP u wfczu cost nd AO BP fazu

A source passing a stationary observer is emitting a frequency of 560 Hz If the speed of sound is 345 m s what must the speed of the source be if the frequency source is 480 Hz 1 Point Option 1

F Light of wavelength 442 nm is sent through a single slit with a width of 884 nm At what angle does the first dark fringe occur 30 degrees 45 degrees 60 degrees 90 degrees Question 12 1 point What does a polarizer do It transmits light rays whose electric fields lie along the transmission axis of the polarizer It rotates light rays such that their electric fields all lie in a single plane It makes the sky appear less blue It blocks light rays that lie along the axis of the polarizer

What is a wave front O the lower half of a wave the upper half of a wave O the front edge of a wave O one complete crest and trough

apart they are driven by one 679 Hz oscillator and therefore emit identical sound waves in phase with one another at the respective points of origin The speed of sound waves in air is 343 m s a A sound engineer wishes to stand in front of one of the speakers at the closest point i e smallest x value where intensity is at a relative maximum At what distance x from the nearest speaker should she position herself Enter your answer in m b The sound engineer now wishes to stand at the closest point along that line where intensity is at a relative minimum At what distance x should she position herself now Enter your answer in m

10 In an investigation to test Thomas Young s double slit experiment a helium neon laser is used to produce an interference pattern on a screen a Use the following measurements to determine the wavelength of light in three different ways T I 4 The angle to the eighth maximum is 3 08 The distance from the slits to the screen is 2 00 m The distance from the first minimum to the fifth minimum is 5 38 cm The distance between the slits is 0 0950 mm The distance from the center of the pattern to the sixth maximum is 8 06 cm

11B Light can be polarized Explain what this means and how it influences our understanding of th type of wave that light is Briefly describe two ways in which light is naturally polarized Describe on application of light polarizing materials

According to the theories of modern physics a photon is a a particle b a wave c a solid flat beam or ray d both a wave and a particle

convex lens of focal length 15 cm is split into two halves and the two halves are placed at a separation of 120 cm Between the two halves of convex lens a plane mirror is placed horizontally and at a distance of 4 mm below the principal axis of the lens halves An object AB of length 2 mm is placed at a distance of 20 cm from one half lens as shown in figure The final image of the point A is formed at a distance of mm 3 from the principle axis Determine the value of n 1 1 20 60 60 3 20 2mm h 3 2 A f 15cm 20 cm tbol 120cm F 15cm 4mm 1 22 1

One side of a glass slab is silvered as show in figure A ray of light is incident on the other side at angle of incidence i 45 R I of glass is 1 5 The deviation of the ray of light from its initial path when it come out of the slab Question Type Single Correct Type 1 2 3 90 110 180 45 1 1 5

Consider the following statements and then mark the incorrect statement s a The actual separation of the fringes increases if the screen is moved towards the plane of the slits b The actual separation of the fringes increases if the monochromatic source is replaced by another monochromatic source of a shorter wavelength c The actual separation of the fringes increases if the separation between the two slits is increased d The sharpness of the fringes increases when the source slit is moved closer to the double slit plane

A beam of light AO is incident on a glass slab 1 54 in a direction as shown in figure The reflected ray OB is passed through a Nicol prism on viewing through a Nicole prism we find on rotating the prism that A 33 N 33 B 1 The intensity is reduced down to zero and remains zero 2 The intensity reduces down some what and rises again 3 There is no change in intensity 4 The intensity gradually reduces to zero and then again increases

lens of focal length 20 cm d convex lens of focal length 20 m 40 Rays from Sun converge at a point 20 cm in front of a concave mirror Where should an objec placed so that size of its real image be twice the size of the object a 20 cm in front of the mirror b 10 cm in front of the mirror d 40 cm in front of the mirror c 30 cm in front of the mirror 41 Which of the following statements about the autotrophs is incorrect a They store carbohydrates in the form of starch b Ti

NE PHYS Q 109 Light rays from a source are incident on a Q 109 glass prism of index of refraction and angle of prisma At near normal incidence the angle of deviation of the emerging rays is 2 1 a 4 2 x 1 2 a 3 1 a stor 1 2 3 1 a au of id af f 2 1 a 4 2 xx

Light waves of intensities and 9 interfere to produce a fringe pattern on a screen The phase difference between the wave at a point P is 3 and 2 at other point Q Then the ratio of intensities at P and Q is 2 Only one correct answer A 3 5 B 5 8 C 1 4

In a double slit experiment the slit separation is 1 mm What should be the width of each of the slits so as to get 20 maxima of the double slit pattern within the central maximum of the single slit pattern A 0 1 mm B 0 2 mm C 0 05 mm D 04mm

from principal axis is equal to the focal length of the mirror The ratio of the distance of point B to the distance of the focus from the centre of curvature is AB is the reflected ray A 3 W N 4 112 fang Ben 1 2 3 N Berafete fare A LTD NIE ER Examy 4

In Young s double slit experiment a slit is covered with thin film so that the optical path difference introduced between coherent waves is 5A Then the new position o central maxima will be at 1 The initial position of 5th maxima 2 The initial position of 3rd minima 3 The initial position of 2nd minima 4 The initial position of 3rd maxima

A lens of power 2D and lens of power 1 D are placed in close contact with each other The combination will behave like i a convergent lens of focal length 50 cm ii a convergent lens of focal length 100 cm iii a divergent lens of focal length 50 cm iv a divergent lens of focal length 100 cm

wavelength 500 10 9 m d 1 10x10 4 m L 2 5 m x distance for 1st dark minimum fringe 0 01136 m theta for dark minimum 0 260 degrees What is the width of the central maximum using sin approxim

Which of the following statements is INCORRECT A When visible light passes through a prism red colour undergoes the least deviation B In an optical fibre the refractive index of the cladding is less than that of the core C For formation of a secondary rainbow light undergoes two internal reflections b from inside a water drop D At sunrise and sunset the sky appears red since red colour undergoes maximum scattering

The diagram below shows a pulse travelling along a rope from X to Y The end Y of the is tied to a fixed support rope X Y When the pulse reaches end Y it will 1 disappear 2 cause the end of the rope at Y to oscillate up and down 3 be reflected and be inverted 4 be reflected and not be inverted

ALLEN 50 In Young s experiment monochromatic light is used to illuminate the two slits A and B Interference fringes are observed on a screen placed in front of the slits Now if a thin glass plate is placed normally in the path of the beam coming from the slit then B 1 The fringes will disappear 2 The fringe width will decrease 3 The fringe width will increase 4 There will be no change in the fringe width