Wave Optics Questions and Answers

ax br 2 abxt Equation of a travelling wave is y 5e a 25 m and b 9 sec A Travelling wave is propagated along x direction B Travelling wave is propagated along x direction C Speed of wave is 3 5 m sec when x y is in meter and t is in D Maximum displacement of particle is 5 m

In a YDSE the upper slit is covered by a thin glass plate of refractive index 1 2 while the lower slit is covered by another glass plate having same thickness but refractive index 1 51 Interference pattern is observed using light of wavelength 4800 It is found that the point P on the screen where the central maxima lies before the glass plate is 3th 4 inserted now has of original intensity It is further observed that fifth maxima earlier lies below point P while sixth minima lies above P The thickness of glass plate is t um Find the value of t YDSE fic 1 2 pc ga K A L T HR C vd Gaf Audi Raz st A913 A U AfKa Guadaic 1 51 ard zan ga af 4800 zu ulazu dfga das qu a far p si chia o cac ant gafaga h du 3fa8 fa da 4 wa ya diam at H 1 G z H 46 df a sta f yd uiaa 31 8 far pa Fed Jafch 50 ASP 342 Feta i c a m ta ma AA Correct Answer 08

The refractive index of glass is 3 2 What is the polarizing angle for glass in degrees Plane polarized light is incident on an analyser The intensity then becomes three fourth The angle of the axis of the analyser with the beam is in degrees Two polarizing sheets have their polarizing directions parallel to each other such that the intensity

WO0028 he equations first wave 36 If intensity ratio of two interfering waves is 9 1 then ratio of maximum to minimum amplitude of resultant wave is 1 2 1 2 3 2 3 1 3 4 5 2 1100005

polarized of water 1 33 in degrees 1 od An analyser is inclined to a polarizer at an angle of 30 The intensity of light emerging from o thaf polarizer is 4 n that is incident on the polarsier Then n is equal to An Cote d A beam of unpolarised light having flux 10 3 watt falls normally on a polarizer of cross section

A person can see clearly objects only when they lie between 50 cm and 400 cm from his eyes In order to increase the maximum distance of distinct vision to infinity the type and power of the correcting lens the person has to use will be 1 convex 2 25 diopter 2 concave 0 25 diopter 3 concave 0 2 diopter 4 convex 0 5 diopter

Red light of wavelength 625 nm is incident normally on an optical diffraction grating with 2x105 lines m Including central principal maxima how many maxima may be observed on a screen which is far from the grating A 15 X

In Young s double slit experiment the separation between the slits is 4A A is the wavelength of the light used The maximum number of maxima formed on the screen placed at a distance of 1 m from the slits is 1 6 2 7 3 9 4 11

A thin film of plastic n 1 56 is 0 25 m thick It is sandwiched between two glass slabs with refractive index of 1 58 and 1 52 respectively White light 400 700 nm is first incident normally on the slab for which n 1 58 If A is the visible wavelength in nm which is missing in the reflected light then find value of 20 in nm tach n 1 56 ych udeft fheo Aus 21 52 Guadaich 2 1 58 c qe zu usfa 0 25 m G faci 2 Add 1 58 Uca ga d fari n 1 58 n 1 56 n 1 52 1 52 chu 400 700 nm Ady ufaa da Muh Ag n u a f nm j uzaffa chI H1 nm 37 X 260

28 Monochromatic red light is shone from above on two soap films A and B as shown below An observer at position X observes that film A appears uniformly red while film B has alternate equally spaced red and black bands K UOBJ 10 4 Soap Film A Soap Film B Which statement best explains these observations A Film A has a thickness of 4 and film B has a thickness of 2 A Film A has a thickness of 2 and film B has a thickness of 4 a b Observer Y C 7 N A A A P N Film A has a thickness much less than and film B has a thickness of 2 d Film A has a constant thickness and film B has a variable thickness blo thinkness and film B has a constant thickness T1

In the following question a statement of assertion A is followed by a statement of the reason R A On increasing the phase difference from to in YDSE the intensity decreases byrd 7 R I 410 cos with usual symbol meanings 1 If both Assertion Reason are true and the reason is the correct explanation of the assertion then mark 1 2 If both Assertion Reason are true but the reason is not the correct explanation of the assertion then mark 2 3 If Assertion is a true statement but Reason is false then mark 3 4 If both Assertion and Reason are false statements then mark 4 1 If both the assertion and the reason are true and the reason is a correct explanation of the assertion 2 If both the assertion and reason are true but the reason is not a correct explanation of the assertion 3 If the assertion is true but the reason is false 4 If both the assertion and reason are false

Q 1 Consider a light beam incident from air to a glass slab at Brewster s angle as shown in the figure 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 polaroid 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 flow All d The intensity of light as seen through the polaroid shall go through a minimum for four orientations of the polaroid Show All From NCERT www arg z 20 Reva University Bangalore Applic App Open Apply Hee

In a Young s double slit experiment the separation between the two slits is d and the wavelength of the light is The intensity of light falling on slit 1 is four times the intensity of light falling on slit 2 Choose the correct choice s n faraz gut at Rd qe che antef 1 KA2 1 42 39f 3 d cha 2 2 92 39fa a m u rT am az g 21 us faccu f cru chi aua Agi A If d the screen will contain only one maximum a uz ham yg 3f8 uy s D Correct Answer B If d 2 at least one more maximum besides the central maximum will be observed on the screen 2o 9 92 h 5 312 38 2 4 318 2 fak dfa dm Correct Answer C If the intensity of light falling on slit 1 is reduced so that it becomes equal to that of slit 2 the intensities of the observed dark and bright fringes will increase afa fait 1 U7 3Tufaa Ichii au A Grau Ga uz f uhu aa avar s Gilg aa fga ata a aut Maag at If the intensity of light falling on slit 2 is increased so that it becomes equal to that of slit 1 the intensities of the observed dark and bright fringes will increase 24uf a a ucher act R a fug faz 1 92 309 da he Aga avar s gily ad dfga ata A Afari at

Out of the following statements which is not correct 1 When upolarised light passes through a Nicol s prism the emergent light is elliptically pola 2 Nicol s prism works on the principle of double refraction and total internal reflection 3 Nicol s prism can be used to produce and analyse polarised light 4 Calcite and Quartz are both doubly refracting crystals

In Young s Double slit experiment a thin glass mica strip of thickness t 152 is pasted infront of slit S If the same strip is now shifted in front of other slit S If the number of fringes which will cross the central point on the screen is N Find N d D d and n 1 5 mica

In a Young s double slit experiment two thin transparent sheets are used in front of the slits S and S t 1 One of thin sheet has refractive index 1 6 and other has 1 4 Both sheets have thickness 2 the central maxima is observed at a distance of 5mm from centre O Now the sheets are replaced by two H H 2 sheets of same material of refractive index but having thickness t and t Now central maxima is observed at a distance 8 mm from centre O Find the thickness of two sheets Given d 1mm D 1m Then

In standard YDSE the ratio of the intensity at the center of a bright fringe to the intensity at a point one quarter of the fringe width from the center is A B YDSE o cafu uz da au a ph dus uz au 2 Correct Answer Your Answer 1 2

In a YDSE setup we plot the phase difference 6 between both waves at point P on the screen against the angular position 0 of point P on the screen The graph is as shown below DATA S A The distance S S 22 B There are a total of 4 minima on the screen T S TU C The first maxima above the centre is at 0 Screen intensity is maximum 4 0 2

In a YDSE set up a thin sheet is placed in front of one of the slits as shown Refractive index of material where 1 x is distance from left edge of sheet and is thickness of sheet If wavelength of light used is 6000 find minimum thickness of sheet for which point O which is symmetrically located records a maxima X of slit varies as Mo

The fringe widths are found to be a and respectively if a Young s double slit experiment is performed in medium of refractive index n and 12 respectively The correct statement is Options 7 if n n if n n2

In a Young s double slit experiment the two slits act as coherent sources of waves of equal amplitude A and wavelength A In another experiment with the same arrangement the two slits are made to act as incoherent sources of waves of same amplitude and wavelength If the intensity at the middle point of the screen in the first case is I and in the second case AIEEE 2011 is I then the ratio 1 2 1 1 is 2 1 3 0 5 4 4

Which statement is not true for the polarization of light 1 Light vibrations are restrained only in one plane 2 Establishes the longitudinal nature of light 3 The intensity of light decreases 4 Both 2 3

In Young s double slit experiment the slits are separated by 0 28 mm and the screen is placed 1 4 m away The width of bright fringe is measured to be 1 2 cm The wavelength of light used in the experiment is 1 2 4 x 10 6 m 3 1 5 x 10 7 m NCERT Pg 364 2 3 x 10 7 m 4 5 x 10 7 m laroids

7 If there are N atoms in a source of Laser light and each atom is emitting light with intensity I then the total intensity produced by it is NCERT Pg 432 1 NI 3 N I 2 N 1 4 MI

Question No 37 Single Correct A A Consider Fraunhofer diffraction pattern obtained with a single slit illuminated at normal incidence At the angular position of the first diffracti minimum the phase difference in radians between the wavelets from the opposite edges of the slit is A A ENGLIS 2n

In Young s double slit experiment the wavelength of light was changed from 7000 to 3500 A While doubling the separation between the slits which of the following is not true for this experiment 1 The width of the fringes changes 2 The colour of bright fringes changes 3 The separation between successive bright fringes changes 4 The separation between successive dark fringes remains unchanged 1 2 We see that your answer is incorrect Please mention reason from below 3 61 4 From NCERT

COFEAINEREN SERENE ORENS E ALLEN 68 The focal length of a convex lens is 10 cm and its refractive index is 1 5 If the radius of curvature of one surface is 7 5 cm the radius of curvature of the second surface will be 1 7 5 cm 2 15 0 cm 3 75 cm 4 5 0 cm GO0068 69 A plano convex lens u 1 5 has radius of curvature 10 cm It is silvered on its plane surface Find focal length after silvering 1 10 cm 2 20 cm 3 15 cm 4 25 cm GO0069 70 A plano convex lens is made of refractive index 75 1 6 The radius of curvature of the curved surface is 60 cm The focal length of the lens is 1 50 cm 2 100 cm 3 200 cm 4 400 cm GO0070 71 If in a plano convex lens the radius of curvature of the convex surface is 10 cm and the focal length of the lens is 30 cm then the refractive index of the material of lens will be 1 1 5 2 1 66 3 1 33 4 3 GO0071 72 If a convex lens of focal length 80 cm and a concave lens of focal length 50 cm are combined together what will be their resulting power 1 6 5 D 2 6 5 D 3 7 5 D 4 0 75 D 73 A convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens Then its focal length will 1 Become zero 2 Become infinite 3 Become small but non zero 4 Remain unchanged GO0073 74 An equiconvex lens is cut into two halves along i XOX and ii YOY as shown in the figure Let f f f be the focal lengths of the complete lens of Pre Medical Physics 59 each half in case i and of each half in case ii respectively Choose the correct statement from the following 1 ff f 2f 2 f 2f f f 77 3 ff f f 4 f 2f f 2f G00074 An object and its real image are located at distances 25 cm and 40 cm respectively from the two principal focii of a convex lens The linear magnification of the image is near to 1 1 3 2 1 3 3 1 8 4 1 8 GO0075 CHROMATIC SPHERICAL ABERRATIONS 76 Lenses applied in achromatic combination having dispersive power in ratio of 5 3 if focal length of concave lens is 15 cm then focal length of other lens will be 1 9 cm 2 9 cm 3 12 cm 4 12 cm GO0076 If the magnitude of dispersive powers of two lenses are 0 024 and 0 036 Then their focal lengths will be for aberration free combination 1 30 cm 40 cm 3 10 cm 30 cm GO0077 GO0072 78 An achromatic convergent doublet of two lenses in contact has a power of 2D The convex lens has a power 5D What is the ratio of the dispersive powers of the convergent and divergent lenses 1 2 5 2 3 5 3 5 2 4 5 3 GO0078 2 30 cm 45 cm 4 20 cm 35 cm 79 The dispersive powers of the materials of the two lenses are in the ratio 4 3 If the achromatic combination of these two lenses in contact is a convex lens of focal length 60 cm then the focal lengths of the component lenses are 1 20 cm and 25 cm 2 20 cm and 25 cm 4 15 cm and 20 cm 3 15 cm and 40 cm GO0079

The figure shows two points sources which emit light of wavelength in phase with each other and are at a distance d 5 5 apart along a line which is perpendicular to a large screen at a distance L from the centre of the source Assume that d is much less than L Which of the following statement s is are correct S S L A Only ten bright fringes appear on the screen B Only six bright fringes appear on the screen C Point y 0 corresponds to bright fringe D Point y 0 corresponds to dark fringe Screen Ty 0 0 S ingro 3mg T mx 29 8 mg 29 3mg

White light is used to illuminate the two slits in Young s experiment The separation between the slits is b and the screen is at a distance d b from the slits At a point directly in front of one of COLORS the slits certain wavelengths are missing The missing wavelength s is are 1 b ld 3 6 3d 2 b 5d 4 All of these

3 otential Increase with increase in frequency Monochromatic light of frequency 6 1014 Hz is produced by a laser The power emitted is 2 x 10 3 W The number of photons emitted per second by source is NCERT Pg 396 1 5 0 1015 2 5 0 1016 3 5 0 1017 4 5 0 1018

electron microscope uses electrons accelerated by a voltage of 50 KV how does the resolving power of this electron microscope compare with that of an optical microscope which uses yellow light INCERT P 411 1 10 times 2 105 times 3 10 times

43 In a double slit experiment n fringes are observed to be formed on a screen placed at a distance D from the slits when light of wavelength is used Now the screen starts moving from rest with constant acceleration a Then the time after which the first maxima disappears from screen and the direction of motion of screen are respectively

c Distinguish between the edge and screw 3 a Monochramatic X rays of 1 51A are incident on a crystal face having an interplaner spacing of 1 61A Find various orders of Bragg s reflections 4 b Carbon is allowed to diffuse through a steel plate 10 mm thick The concentrations of carbon at TC the meninonential and

A beam of electrons is used in young s double experiment If the speed of electrons is increase then the fringe width will 1 decrease 2 increase 3 fringe will not be seen 4 remain same

represent two snaps of a travelling wave on a string of mass per m 0 25 kg m The two snaps are taken at time t 0 and t 1 24 y mm 10 5 5 10 t 0 Figure I A speed of wave is 4m s B the tension in the string is 4N m y mm 10 5 Fu 2 V 5 10 C the equation of the wave is y 10 sin x 4 t s Then T D the maximum velocity of the particle 25 m s t G x m Figure II S 24 V 4 orkes fim 1084 10 108 11 40 TI LOS N WA

1 5 Calculate the wavelength and frequency of He line of Balmer series for hydrogen atom What is the least amount of energy eV that should be given to H atom in ground state so that it can emi He line in Balmer series

74 Wave Optics White light is used in Young s double slit experiment Separation between slits is y and the screen is at distance x from slits x y Which of these wavelengths is missing in front of one of the slits 1 3 y X y 4x y 2 aemit 2x ile ordubb erit 4 All of these Shape of interference fringes formed on the screen due to point source 1 3 A C

Diffraction of sound wave is more prominent in daily life compared to that of light wave because 1 Light has larger wavelength 2 Sound has larger wavelength 3 Both have large wavelength 4 Both have small wavelength

39 Magnifications of image of an object at two different positions of a convex lens is 4 and 2 If displacement between positions is 20 cm focal length of lens is 1 10 cm 3 40 cm 2 20 cm 4 30 cm

wo coherent point sources of light wave S and S produce light of same frequency uHz and wavelength A cm with amplitude A m Each circular arc represents a wavefront at a particular time and is separated from next arc by a distance A 2 cm Both the light waves propagate through the medium and interfere with each other Read aragraph carefully and answer the following questions r X 2 cm S R OR M Z O H W V U B S C E

Two coherent point sources of light wave S1 and S2 produce light of same frequency Hz and wavelength cm with amplitude A m Each circular arc represents a wavefront at a particular time and is separated from next arc by a distance 1 2 cm Both the light waves propagate through the medium and interfere with each other Read paragraph carefully and answer the following questions r 2 2 cm R O 10 O 12 13 O 14 G S OR M N O P W V U L B S C E How many of the points shown in the figure represent maxima

UUDIS In a YDSE Young s double slit experiment screen is placed Im from the slits wavelength of light used is 6000 Fringes formed on the screen are observed by a student sitting close to the slits The student s eye can distinguish two neighbouring fringes if they subtend an angle more than 1 minute of arc Calculate the maximum distance between the slits so that fringes are clearly visible 0 163

An object S is placed at a distance of 20 cm from a convex lens of focal length 15 cm as shown in the figure where should a convex mirror of focal length 25 cm be placed from the lens so that a real image is formed on the object itself 20 cm S 20 cm 10 cm 40 cm x 25 cm M

Light from a source consists of two wavelength A 6500 and 5200 If D 2m and d 6 5mm find the minimum value of y 0 where the maxima of both the wavelengths coincide 0 4mm 0 2mm 0 8mm 0 5mm

Where should an object be placed in front of a convex lens to get a real image of the size of the object a At the principal focus of the lens b At twice the focal length c At infinity d Between the optical centre of the lens and its principal focus

Two loudspeakers L and L2 driven by a common oscillator and amplifier are arranged as shown in fig The frequency of the oscillator is gradually increased from zero and the detector at D records a series of maxima and minima If speed of sound is 330 m s then the frequency at which the first maximum is observed is 165 Hz 330 Hz 495 Hz L L

In young s double slit experiment the slits are placed 0 240nm apart Light of wavelength 500nm is incident on the slits The total number of bright fringes that are observed in the angular range 30 0 30 is 240 481 241 483

A convex lens has focal length 20cm at what distance from the lens should the object be placed so that the image for med is 40 cm on the other side of the le ns Also state the nature of the image formed

separte by a distance of 1 mm are illuminated with red light of wavelength 6 5 10 m The interference fringe are observed on a screen placed Im from the slits The distance between third dark fringe and the seventh dark fringe is equal to 1 0 65 mm 2 2 6 mm 4 4 88 mm 8 3 3 25 mm H He and O are projected in uniform 9 field with A Iften f6 5 10 fatten 1 0 65 mm 3 3 25 mm H He a O va una scia fo 2 2 6 mm 4 4 88 mm fava

There is a mark at the base of an empty beaker The mark is focussed with the help of a microscope from above If tur pentine oil of 4 cm height is poured in the beaker the micro scope is to be raised by 1 28 cm upwards to focus the mark Determine the refractive index of the turpentine oil 1 47