# Optical Instruments Questions and Answers

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5 Prism angle of glass prism is 10 It s refractive index of red and violet colour is 1 51 and 1 52 respectively Then its dispersive power will be 1 0 015 2 0 020 3 0 011 4 0 019
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Question 14 A simple screw jack used in actual practice is A non reversible machine A reversible machine An ideal machine not a lifting machine
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A converging lens of focal length 15 cm and a converging mirror of focal length 20 cm are placed with their principal axes coinciding A point source S is placed on the principal axis at a distance of 12 cm from the lens as shown in figure It is found that the final beam comes out parallel to the principal axis Let the separation between the mirror and the lens be 10 x k Find k AA S 1 M S P 5
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A divergent lens has a focal length of 20 cm At what distance should an object of height 4 cm from the optical centre of the lens be placed so that its image is formed 10 cm away from the lens Find the size of the image also
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Q 2 A short straight object of length lies along the central axis of a spherical concave mirror at a distance X from the mirror The focal length of the mirror is F If the length of the image in the mirror is then ratio 9 is Assume X and F D w Soup ba straight X rod doja alusy v F gewann allusz t s cov on 7 1 X Boat FJS
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Example 9 12 a The near point of a hypermetropic person is 75 cm from the eye What is the power of the lens required to enable the person to read clearly a book held at 25 cm from the eye b In what way does the corrective lens help the above person Does the lens magnify objects held near the eye c The above person prefers to remove the spectacles while looking at the sky Explain why Solution a u 25 cm v 75 cm 1 f 1 25 1 75 i e f 37 5 cm The corrective lens needs to have a converging power of 2 67 dioptres b The corrective lens produces a virtual image at 75 cm of an object at 25 cm The angular size of this image is the same as that of the object In this sense the lens does not magnify the object but merely brings the object to the near point of the hypermetric eye which then gets focussed on the retina However the angular size is greater than that of the same object at the near point 75 cm viewed without the spectacles c A hypermetropic eye may have normal far point i e it may have
Physics
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An object is placed at a distance of 20 cm from a co axial combination of two lenses A and B The combination of the lenses forms a real image which is four times the size of the object If lens B is concave with a focal length of 48 cm then what is the nature and focal length of lens A convex 12 cm convex 6 cm O O concave 12 cm convex 18 cm
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03 In a vernier callipers ten smallest divisions of the vernier scale are equal to nine smallest 10 division on the main scale If the smallest division on the main scale is half millimeter then the vernier constant is A 0 5 mm C 0 05 mm B 0 1 mm D 0 005 mm
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1 A parallel beam of monochromatic light of wavelength 5000A 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 in focal plane The first minimum will be formed for the angle of diffraction equal to a 0 b 15 1993 c 30 d 50
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2 Assertion A Focal length of a spherical mirror does not dpend on the material from which mirror is made but same for the lens depends on the material of lens Reason R law of reflection does not dpend on material and surrounding but law of refraction depends on refractive index of th materials Section R
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Assertion A A reflecting type telescope is preferred over refracting type in astronomy Reason R reflecting type telescope is free from chromatic aberration and parabolic surfaces are us to avoid spherical aberration
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4 Red green white The effective area of a black body is 0 1 m and its temperature is 100 K The amount of radiations emitted by min is 1 1 34 cal 2 8 1 cal 3 5 63 cal 4 1 34 J
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A convave mirror of focal length 200cm is used to obtain the image of the sun which subtends an angle of 30 Then the diameter of the image of the solar disc is 200cm and add at at fafara sick an for A 13 48cm B 1 75cm C 9 87cm D 20 0cm Your Answer 30
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rying power In a laboratory four convex lenses L L L and L of focal lengths 2 4 6 and 8 cm respectively are available Two of these lenses form a telescope of length 10 cm and magnifying power 4 The objective and eye lenses are respec RPMT 2008 tively 1 L L3 2 L L 3 L L 4 L L principal axis If the power of
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4 microscope will decrease but that of telescope In an astronomical telescope in normal adjustment a straight black line of length L is drawn on inside part of objective lens The eye piece forms a real image of this line The length of this image is I The magnification of the telescope is 2 L I 4 1 NEET 2015 1 L 1 L I of the
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An object is placed at a distance of 20 cm in rarer medium from the pole of a convex spherical refracting surface of radius of curvature 10 cm If the refrective index of the rarer medium is 1 and of the refracting medium is 2 then the position of the image is at 1 40 3 cm from the pole inside the denser medium 2 40 cm from the pole inside the denser medium 3 40 3 cm from the pole outside the denser medium 4 40 cm from the pole outside the denser medium
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1 20 cm 2 16 cm 3 10 cm 4 12 cm A convex lens forms a real image 9 cm long on a screen Without altering the position of the object and the screen th lens is displaced and we get again a real image 4 cm long on the screen Then the length of the object is 1 9 cm 4 36 cm 2 4 cm 3 6 cm hinnt in placed at a distance of 5 cm from a convex lens of focal length 10 cm then the image is
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18 The ray diagram could be correct n Lens 2 If n n and n n n 1 If n n n If n n and n n 4 Under no circumstances Rafr
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5 1 10 cm 2 20 cm 3 5 cm 4 none of these A thin linear object of size 1 mm is kept along the principal axis of a convex lens of focal length 10 cm The object is at 15 cm from the lens The length of the image is 1 1 mm 2 4 mm 4 8 mm The ray diagram could be correct 3 2 mm
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2 Two similar thin equi convex lenses of focal length feach are kept coaxially in contact with each other such that the focal length of the combination is F When the space between the two lenses is filled with glycerin which has the same refractive index u 1 5 as that of glass then the equivalent focal length is F The ratio F F will be 1 2 1 2 1 2 3 2 3 4 3 4 Two parallel infinite line chora with lingor
Physics
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A parallel beam of light 5000 is incident at an angle x 30 with the normal to the slit plane in a young s double slit experiment Assume that the intensity due to each slit at any point on the screen is lo point O is equidistant from S and S2 The distance between slits is 1 mm A Intensity at O is 4lo B Intensity at O is zero e The intensity at a point on the screen 1m below O is 4lo D The intensity at a point on the screen 1m below O is zero S 3m
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To improve resolving power of a telescope a increase aperture of lens b increase wavelength of light c decrease aperture of lens d decrease wavelength of light Question Type Single Correct Type 1 a b 2 a d
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n accordance with Kirchhoff s law for a black body radiation which one is wrong Bad absorber is a bad emitter Bad reflector is a good emitter Bad emitter is a good absorber
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A student used a device X to obtain focus the image of a well illuminated distant building on a screen S as shown below in the diagram Select the correct statement about the device X S 8 cm A This device is a concave lens of focal length 8 cm B This device is a convex mirror of focal length 8 cm C This device is a convex lens of focal length 4 cm D This device is a convex lens of focal length 8 cm
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5 points An optical power of 0 5mW is initially launched into an optical fibre The power level is found to be 0 0199mW after 4 km The attenuation coefficient in this fibre will be 1 5 dB km 2 5 dB km 3 5 dB km 345 dB km Save Answer
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An analyser blocks the light coming from a polariser as Select one a None b The pass axis of the analyser and the polariser is oriented 90 to each other e The light changes it path as it passes through the analyser d The pass axis of the analyser and the polariser is oriented 0 to each other
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An air bubble in sphere having 4 cm diameter appears 1 cr from surface nearest to eye when looked along diameter aHg 1 5 the distance of bubble from refracting surface is A B C D 1 2 cm 3 2 cm 2 8cm 1 6 cm My Answer
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B In telescope which mirror is used as objective instead of convex lens 1 Parabolic concav mirror 2 Plane mirror 3 Convex mirror 4 Mirror can t be used
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Two mirrors one concave and the other convex are placed 60 cm apart with their reflecting surfaces facing each other An object is placed 30 cm from the pole of either of them on the axis If the focal lengths of both the mirrors are 15 cm the position of the image formed by reflection first at the convex and then at the concave mirrors is ONO 19 09 cm from the pole of the convex mirror 19 09 cm from the pole of the concave mirror 11 09 cm from the pole of the concave mirror 11 cm from the pola of the convex mirror
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The magnifying power of a compound microscope is high if x Both objective and eyepiece are of high focal length Objective has long focal length and eyepiece small Objective of short and eyepiece are of very large focal length
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OPTICS PHYSICS X APT 2021 22 13 Athin prism has different medium on its either side A light ray is incident almost normally on the first face What is the angle of deviation if all the angles are very small 0 1 1 A 1 4 0 1 1 1 A 1 1 c 1 A 1 A 12 sixe jed
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A convex mirror and a concave mirror of radius 10 cm each are placed 15 cm apar facing each other An object is placed midway between them If the reflection first takes place in the concave mirror and then in convex mirror the distance of the final image from the pole of the convex mirror in cm is
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The monochromatic beam of light is incident at 60 on one face of an equilateral prism of refractive index n and emerges from the opposite face making an angle 8 n with the normal see the figure For n 3 the value of 0 is 60 de and m The value of m is dn 60 Correct answer 2
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C 1 D same as of radius of curvature A light of ray incidents normally on one side of equilateral prism If refractive index of prism 1 5 then deviation angle is person or for A 30 B 60 C 45 D 75
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A plano convex lens has index of refraction n The curved side of the lens has radius of curvature R and rests on a flat glass surface of the same index of refraction with a film of index nfilm between them as shown in Fig 37 18a The lens is illuminated from above by light of wavelength A Show that the dark Newton s rings have radii given approximately by m R n film
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Lateral magnification of objective of compound microscope is 100 and angular magnification of its eyepiece is 20 The magnifying power of compound microscope is 1 120 2 5 3 2000 4 1000 ting lons of a terrestrial telescope are 20 cm 10 cm and 0
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minimum angle of deviation is also A then in terms of refractive index mothongo mathoriga mothonga mathongo mathonnomathango 1 2 cos 9 2 sin mathongs mathango mathongemathongo mathongo mathongozion mathongo Math Bole Toh MathonGo www mathongo com mathongo mothongo mathango
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A material having an index of refraction of 1 30 is used as an antireflective coating on a piece of glass n 1 50 What should be the minimum thickness of this film in order to minimize reflection of 500 nm light
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A glass sphere of refractive index 1 5 forms the real image of object O at point I as shown in the figure when kept in air of refractive index 1 If the value of x is KR Find k Ho 1 0 X 1 5 C Mo 1 0 R
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For observing a cricket match binoculars are preferred to a terrestrial telescope because 1 the binoculars give the proper three dimensions 2 the binoculars have a shorter length 3 the telescope does not give erect image 4 the telescope has chromatic aberration
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Choose true or false for each statement regarding the sign conventions for mirrors Real images appear in front of a mirror and have a positive value for the image distance Real images appear in front of a mirror and have a negative value for the image distance Virtual images appear appear behind a mirror and have a negative value for the image distance Submit Answer Tries 0 2
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GET PRE MEDICAL 2021 NEET LEADER PHASE IV INTENAL light ray is ned by 10 the angle TEST 01 07 10 2020 A plane mirror is inclined at an angle with the horizontal If a ray of light is incident at an angle 0 then the reflected ray makes the following angle with the horizontal 1 0 2 0 2 20
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Aakash Rank Booster Test Series for NEET 2020 28 The length of the optical path of two media in contact of length d and d of refractive index Hy and H respectively is 1 d d d d M 9 A ray of light falls on a transparent sphere with 3 2 d H d d d H 4 4
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30 Light is incident normally on face AB of a prism as shown in figure A liquid of refractive index u is placed on face AC of the prism the prism is made of glass of refractive index The limit of 1 for which total internal reflection takes place on face AC is A 3 4 3 3 60 Liquid 90 B 30 3 2 2 4 2 C 3 3 4 7 3 4
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Sir ere ame from 8 and 1 When two thin lenses are in contact their combined power is 9 D When they are 27 separated by a small distance of 20 cm their equivalent power becomes D Their individuals power in dioptre is 6 and 3 5 and 4 7 and 2 Solution Answer 2 P1 P 9 27 P P 5 M 20 100 his P P ked Torr TO 2 7 9 1 PP P P 18 5 P P P P 4P P2 81 18 4 C
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A transparent solid cylindrical rod has a refractive index u and is surrounded by air A light ray is incident at mid point of one end of rod as shown If 0 is angle of incident then u for grazing a light along the walls is sine 2 3 0 1 3 W W N Z 1 3 2 1 O 4 3
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4 Both 1 and 2 10 An astronomical telescope has magnification 8 for normal adjustment A person using this telescope finds that when distance between objective and eyepiece is made 40 cm the final image is formed at infinity Select the correct pair of focal lengths of objective and eyepiece respectively of 5 cm from the lens 40 1 f cm fe 9 9 2 f 10 cm f 30 cm 3 f 320 9 cm fe 320 cm 40 STENG DITE 9 4 f 30 cm f 10 cm cm
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The coordinate of a point where parallel rays are focussed by the thin convex lens is where focal length of convex lens is 10 cm and it is placed along y axis WENKE 45 1 10 10 cm YA ENDERE P O C NS 2 10 20 cm
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A convex lens of focal length 10 cm can pro duce a i magnified virtual image ii magnified real image If yes then where shall the object be placed in each case for obtaining these images Explain using di agrams
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3 Assume that scientists have discovered a new force measured in Newton say F between any two objects They found that the force is proportional to the densities of the two objects and inversely proportional to the square of distance between them So the equation looks d d like Fp K where d d2 are densities of the objects and r is the distance between them 72 Suppose the dimensions of K are M L Tc Then a b c