Wave Optics Questions and Answers

separate set ups of the young s double slit experiment fringes of equal width are observed when light of wavelengths in the ratio 1 2 are used If the ratio of the slit separation in the two cases is 2 1 the ratio of the distances between the plane of the slits and the screen in the two set ups is a 4 1 b 1 1 c 1 4 d 6 d 2 1

For a wavelength 6000 incident normally 7 fringes appear in thin film of air between two points What is difference of thickness between these points A 3 2 1061 m B 2 1 x 10 m C 2 9 x 10 m D 2 5 x 10 m

in the two cases is 2 1 the of the distances between the plane of the slits and the screen in the two set ups is a 4 1 b 1 1 d 2 1 19 A thin mica sheet of thickness 2 x 10 m and refractive index 1 5 is introduced in the path of the first wave The wavelength of the wave used is 5000 A The central bright maximum will shift a 2 fringes upward b 2 fringes downward c 10 fringes upward d None of these c 1 4

15 If an interference pattern has maximum and minimum intensities in 36 1 ratio then what will be the ratio of amplitudes a 5 7 16 Monochromatic b 7 4 c 4 7 d 7 5

In young s double slit experiment the intensity of light coming from the first slit is double the intensity from the second slit The ratio of the maximum intensity to the minimum intensity on the interference fringe pattern observed is a 34 b 40 3 In young s double clit c 25 d 38

25 Young s double slit experiment is carried out by using green red and blue light one colour at a time The fringe width recorded are B B Brespectively Then R a BG BB BR C BR BB BG 6 Two slits are b BB BG BR d BR BG BB separated by CO5

3 Light from n incoherent sources of intensity I 21 31 nI are super imposed in a region Resultant intensity at a point in the region of superposition will be 1 Zero 2 nI n n 1 3 2 4 Can not be determined 200 need A

d Same at all points 4 The young s double slit experiment is performed with light of wavelength 6000 where in 16 fringes occupy a certain region on the screen If 24 fringes occupy the same region with another light of wavelength then can is a 6000 c 5000 b 4500 d 4000 im ming t meter

5 Two coherent sources emit light beams of intensities 91 and 161 respectively If intensity of second source is made same as first ratio of fringe visibilities will be A 24 25 C 19 21 B 17 18 D 25 26

Sir i did not understand this ques pl z explain step by step how do we de al with such types of questions An arrangement for YDSE is shown in figure S is a light source then find the position of central maxima from point O on screen B f 20 cm D 80 cm 1m Screen A S 1 mm 20 cm lo 3 mm 5 mm below O O Screen B

6 Light of wavelength 600 nm is incident on an aperture of size 2mm What will be the distance upto which the ray of light can travel such that its spread is less than the size of the aperture Con a 6 67 m b 7 m c 8 m d 6 2 m

a a d 4 13 In a YDSE experiment if a slab whose refractive index can be varied is placed in front of one of the slits Assume slits of equal width and there is no of screen with u will be best represented by 21 then the variation of resultant intensity at mid point c 11 lo 1 b d 2 1 lo inte vi Indon b d 1 10

12 In the figure shown if a parallel beam of white light is incident on the plane of the slits then the distance of the nearest white spot on the screen from O is assume d D d od 8 3750 a d 4 VnGT Barg 2d 3 b d 2 D O golovay dah c d 3 d d 6

15 A single slit of width 0 20 mm is illuminated with light of wavelength 500nm The observing screen is placed 80cm from the slit The width of the central bright fringe will be a 1 mm b 5 mm c 10 mm d 4 mm

8 Two identical coherent sources placed on a diameter of a circle of radius R at separation x R symmetrically about the centre of the circle The sources emit identical wavelength each The number of points on the circle with maximum intensity is x 5 a 20 c 24 b 22 d 26

c Both of these d None of these 42 A parallel beam of monochromatic light of wavelength 5000A is incident normally on a single narrow slit of width 0 001mm The light is focused by a convex lens on a screen placed on the focal plane The first minima will be formed for the angle of diffraction equal to a 0 b 15 c 30 d 60

a 3 0 b lo c 5 0 d 9 0 11 Two coherent light sources each of wavelength are separated by a distance 3 The maximum number of 32 minimas formed on line AB which runs from a 2 c 6 0 to o is b 4 d 8

65 The graph showing the dependence of intensity of light on the angle between polariser and transmitted analyser is To 45 90 135 180 0 H 45 90 135 180 b d 45 90 135 180 0 45 90 135 180 In the light at is is intens be a K C KI In Yc

If a transparent parallel plate of uniform thickness t and refractive index u is interposed perpendicularly in the path of a light beam the optical path is a increased by u 1 t b decreased by ut c decreased by u 1 t d increased by ut

transparent film of micaand glass are put in the path of two waves If their thickness are 3t and 2t respectively What should be refractive index of mica so that central maximum is found at O glass 1 5 3t H a u 125 S S 2t D h 15 O 10 mr 20 m doub

13 In a Fraunhofer diffraction at a single slit of width d with incident light of wavelength 5500 the first minima is observed at an angle 30 The first secondary maxima is observed at an angle 0 equals a sin c sin 1 2 3 4 b sin 4 1 d sin 3 2

A beam of light consisting of two wavelengths 560 nm and 420 nm is used to obtain interference fringes in a Young s double slit experiment Find the least distance from the central maxima where the bright fringes due to both the wavelengths coincide The distance between the two slits is 4 mm and the screen is at a distance of 1 m from the slits a 2 21 mm c 5 22 mm b 0 42 mm d 2 cm 2 cm

A Young s double slit set up for interference is shifted from air to within water then the fringe width a Becomes infinite b Decreases c Increases d Remain unchanged C 21 n L nl 10 A parallel beann normally on a nat on a screen place incident beam A

15 Two coherent sources S and S are separated by 1 5 A Interference fringes are observed on circular screen as shown The total number of minima observed is S and S are equidistance from O a Four c Six S O S 1 52 b Two d Infinite

25 Two slits S and S illuminated by a white light 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 effected then ratio of the thickness of the two sheets will be a 1 2 c 1 4 b 2 1 d 4 1

22 In a Young s interference experimental arrangement incident yellow light is composed of two wavelength 5890 and 5895 Distance between the slits is 1 mm and the screen is placed 1 m away Order upto which fringes can be seen on the screen will be a 384 b 486 c 512 d 589

A converging lens of focal length 15 cm is placed coaxially in front of a concave mirror of focal length 37 5 cm at a distance of 15 cm from the mirror An object O is placed at a distance of 12 cm from the lens Locate the final image formed by this lens mirror combination 15 cm 12 cm Converging lens Concave mirror

25 A plane wavefront 2 6 x 10 7m falls On a slit 0 4 mm wide A convex lens of focal ength 0 8m placed behind the slit focusses the light on a screen What is the linear diameter of second maximum a 6mm b 12mm c 3mm d 9mm z 6X10 7 d 0 4 mm x 10 D f 0 8 Y 25 DN 5x0 29 2 x

1 In case of interference the energy is redistributed 2 In case of interference the sources emit waves of nearly same frequency 3 The production of beats is the result of constructive interference only 4 All of these

2 Assertion Though light of a single frequency monochromatic is incident on a metal the energies of emitted photoelectrons are different Reason The energy of electrons emitted from inside the metal surface is lost in collision with the other atoms in the metal

Problem 8 Laser light of wavelength 630 nm incident on a pair of slits produces an interference pattern in which the bright fringes are separated by 8 1 mm A second light produces an interference pattern in which the fringes are separated by 7 2 mm Calculate the wavelength of second light Delhi 2000C

In the figure shown all pulleys are light and there is no friction between pulley and strings Masses m m 2kg and all strings have a linear mass density 3 x 10 kg m which makes masses of strings negligibly small compared to m m Initially separation between pulley P and mass m is 20 cm At this instant system is released from rest and a transvers pulse is created at the location of m A Pulse will reach P in time 0 01 s C Pulse will reach P in time 1 s P m B Pulse will reach P in time 0 1 s D Pulse will reach P in time 10 s m

Problem 6 The minimum deviation produced by a glass prism of angle 60 is 30 If the velocity of light in vacuum is 3 x 1010 cm sec calculate the velocity of light in glass

The Brewster angle for the glass air interface is 54 74 If a ray of light going from air to glass strikes at an angle of incidence 45 then the angle of refraction is Hint tan 54 74 2 1 60 2 30 3 25 4 54 74

In a YDSE setup we plot the phase difference between both waves at point P on the screen against the angular position e of point P on the screen The graph is as shown below S S 0 Screen Your Answer ABD Answer A BC Solution 4x 0 x12 A The distance S S 2 B There are a total of 4 minima on the screen C The first maxima above the centre 5 at 8 D The consecutive maxima on the screen maintain same distance From 2nd graph when p 4 then path difference 22 distance between S and S At 8 d sin 8 2A 2 2

A beam of monochromatic green light is diffracted by a slit of width 0 550mm The diffraction pattern forms on a wall 2 06m beyond the slit The distance between the positions of zero intensity on both sides of central bright fringe is 4 10mm Wavelength of the light used is 1 400nm 2 525nm 3 642nm LAN 547pm omspris116 edi habiano05

A special kind of light bulb emits monochromatic light of wavelength 700 nm Electrical energy supply to it at the rate of 60 W and the bulb is 50 efficient at converting that energy to light energy How many photons are emitted by the bulb during its life time of 1 day

ht of 2 different wavelengths 632nm and 474 nm passes through a single slit of width 7 15 10 5 m The two diffraction patterns are observed on a screen 1 2 m away Find the first position distance measured from the central ge where a dark fringe of one pattern falls on top of a dark fringe of the second pattern 3 2 cm 4mm 1 6 cm

The light waves having having wave wave equations y 10Sin wt kx and y 5Sin kx wt o interfere The ratio of maximum to the minimum intensity of light in the interference pattern is 2 3 1 4 81 1 1 9 1 3 2 1

8 In a Newton s ring experiment setup the diameter of the third ring has been found to be 0 2 cm and th of the twentieth ring 0 7 cm The radius of curvature of the Plano convex lens is 90 cm the wavelength o b 7 25X105 cm c 7 35X105 cm d 7 45X105 cm the light used is a 7 15X105 cm

In young s double slit experiment relative intensity at a point on the screen may be defined as ratio of intensity at that point to the maximum intensity on the screen Light of wavelength 7500 passing through a double slit produces interference pattern of relative intensity variation as shown in figure 0 on horizontal axis represents the angular position of a point on the screen then the ratio of amplitudes of the two waves producing interference pattern on the screen is Relative intensity I m 1 0 0 05 10 15 2 0 in degree

Light with average flux of 50 W cm2 falls normally on non reflecting surface at normal incident having surface area 10 cm2 The energy received by the surface during time span of one minutes is O 104 J O 3 x 104 J 06 10 J O 5 10 J

10 1 Consider a light beam incident from air to a glass slab at Brewster s angle as shown in the figure P A polaroid is placed in the path of the emergent ray at point P and rotated about an axis passing through the centre and perpendicular to the plane of the polaroid a For a particular orientation there shall be darkness as observed through the polaoid b The intensity of light as seen through the polaroid shall be independent of the rotation c The intensity of light as seen through the Polaroid shall go through a minimum but not zero for two orientations of the polaroid d The intensity of light as seen through the polaroid shall go through a minimum for four orientations of the polaroid

For the following questions assume the wavelengths of visible light range from 380 nm to 760 nm in a vacuum a What is the smallest separation in nm between two slits that will produce an eighth order maximum for any visible light nm b What is the smallest separation in nm between two slits that will produce an eighth order maximum for all visible light nm

What do you understand by interference of light Two waves with amplitudes al and 92 and angular frequency o are imposed Find the intensity in case of constructive interference and destructive interference

iii In Newton s rings experiment the diameter of 5th dark ring is reduced to half of its value after placing a liquid between plane glass plate and convex surface Calculate the refractive index of the liquid

A glass rod of refractive index 1 5 has ends as shown in figure below The object O is at a distance 2R from the surface of larger radius of curvature The distance between the apexes of the end is 3R What is 4 marks the distance of image point of O from the right hand vortex B if R 20 cm R 2 Air 2R A GLASS M 3R B Air

In the young s double slit experiment the intensity at the central maxima is observed to be lo If one of the slits is covered then intensity at the central maxima will become Question Type Single Correct Type 1 2 2 lo 2

8 A Newton s ring arrangement is used with a source emitting two wavelengths 21 6000 A and 22 5000 A and it is found that nth dark ring due to 21 coincides with n 1 th dark ring for 22 If radius of curvature of the curved surface is 90 cm find the diameter of nth dark ring for 21 4 marks

Example 26 An unpolarized light is successively passed through two polaroids each with their transmission axis parallel If the intensity of unpolarized light be lo then intensity of the light after emerging from second polarizer will be Solution Unpolarized Transmission axis 22 0 Polarized light Final emergent light