Optical Instruments Questions and Answers

This question concerns a symmetrical lens shown along with its two focal points It is made of glass with n 1 2 and has focal length f Four different region are shown A B Here A 0 x f B f x 0 C 0 x f D f x C Air n 1 F D If an object is placed somewhere in region A in which region does the image appear

A double convex lens made of a material of refractive index 1 5 and having a focal length of 10 cm is immersed in a liquid of refractive index 3 0 The lens will behave as a converging lens of focal length 10 cm b diverging lens of focal length 10 cm c converging lens of focal length 10 3 cm d diverging lens of focal length 10 3 cm

A 5 0 dioptre lens forms virtual image which is four times the object placed perpendicularly on the principal axis of the lens The distance of the object from the lens is found to be 10 X cm Determine X Write an answer

Q 13 In a vernier callipers ten smallest divisions of the vernier scale are equal to nine smallest division on the main scale If the smallest division on the main scale is half millimeter then the Least Count of Vernier Callipers is 1 0 5 mm 2 0 1 mm 3 0 05 mm 4 0 005 mm

The refractive indices of a thin prism for red violet and yellow lights are 1 52 1 62 and 1 59 respectively If mean deviation is 4 what is angular dispersion produced by prism 0 68 4 52 2 80 0 98

In an astronomical telescope focal length of objective lens is 75 cm and that of eye piece is 5 cm What is magnifying power if final image is seen at 25 cm from eye 18 22 O 15

Two coherent monochromatic light waves of amplitude 3A and 2A interfere at a point on screen having a phase difference of rad The resultant intensity at that point will 3 be proportional to 5 A 13 A 19 A

When a pin is moved along the principal axis of a small concave mirror the image position coincides with the object at a point 0 5 m from the mirror refer figure If the mirror is placed at a depth of 0 2 m in a transparent liquid the same phenomenon occurs when the pin is placed 0 4 m from the mirror The refractive index of the liquid is A 6 5 H B 5 4 0 2 m 0 2 m C 4 3 D 3 2

The diagram below shows a lens as a combination of a glass block and two prisms X A B X i Name the lens formed by the combination ii What is the line XX called iii Complete the ray diagram and show the path of the incident ray AB after passing through the lens iv The final emergent ray will either meet XX at a point

42 A plano convex glass lens 3 2 of radius of curvature R 20 cm is placed at a distance of b from a concave lens of focal length 10 cm of A a What should be the distance a of a point object O from the plano convex lens so that the position of final image is independent of b 1 30 cm 2 20 cm 3 40 cm 4 60 cm elegram pee

A compound microscope with an objective of 1 0cm focal length and eyepiece 2 0cm Focal length of a tube is 20cm Calculate the magnifying power of the microscope i 270 ii 27 iii 140 iv 14

A light ray is incident on a plane mirror at ar angle of incidence of 30 as shown in the figure The mirror is rotated by 45 in the clockwise direction Calculate the angle by which the reflected ray deviates from its original path Incident Ray 30 I 1 I

4 A parallel beam of light is incident from air at an angle a on the side PQ of a right angled triangular prism of refractive index n 2 Light undergoes total internal reflection in the prism at the face PR when a has a minimum value of 45 The angle 9 of the prism is A 15 B 22 5 0 n 2 R C 30 45

5 Two plane mirrors P and Q are kept parallel to each other as shown in the figure A light ray is incident at an angle 60 at a point just inside one end of mirror P The plane of incidence coincides with the plane of the figure Then the maximum number of times the ray undergoes reflections including the first one before it emerges out it 2 3m 0 2 m a 60

0 8 In an fcc unit cell atoms are numbered as shown below The atoms not touching each other are Atom numbered 3 is face centre of front face 1 3 and 4 3 1 and 2 The nuk 3 2 2 1 and 3 4 2 and 4

Which statement about a moving object is correct A When an object is accelerating the resultant force acting on it must equal zero B When an object is moving at a steady speed the air resistance acting on it must equi zero C When an object is moving at a steady speed the resultant force acting on it must equa zero D When an object is moving there must be a resultant force acting on it

3 4 0cm 4 3 0cm An object is moving towards a concave mirror of focal length 24 cm When it is at a distance of 60 cm from the mirror its speed is 9cm s the speed of its image at that instant is 1 4 cm s towards the mirror 2 9 cm s towards the mirror 3 4 cm s away from the mirror 4 9 cm s away from the mirror

he ratio of am is top end n figure When the h he can ve index A point object is placed at distance of 20 cm from a thin plano convex lens of focal length 15 cm The plane surface of the lens is now silvered The image created by the system is at 20cm 1 60 cm to the left of the system 2 60 cm to the right of the system 3 12 cm to the left of the system 4 12 cm to the right of the system ACDE questiongat

An equiconvex lens 3 2 is placed over a plane mirror as indicated in diagram An object placed 12 cm from system such that image and object coincide Now a liquid is poured between mirror and lens and for the same object the image now formed at 24 cm from mirror The refractive index of the liquid poured will be A RAM B 4 12cm O C 2 3 u 3 2 VATH D

2 13 The dispersive powers of flint glass and crown glass are 0 053 and 0 034 respectively and their mean refractive indices are 1 68 and 1 53 for white light Calculate the angle of the flint glass prism required to form an achromatic combination with a crown glass prism of refracting angle 4 1 2 2 4 3 5 4 6

2 Light of wavelength 5000 is incident normally on a plane transmission grating Find the difference in deviations in the first and third order spectra The number of lines per cm on the grating surface is 6000

PASSAGE A step index fiber is made with a core of refractive index 1 36 a diameter of 49 m and a fractional refractive index change of 0 025 it is operated at a wavelength of 1 3um Choose the correct options Marks 2 The normalized frequency of the fiber is OPTIONS 25 7

Resolving power of compound microscope is given by symbols have their usual meaning d 1 d de 1 de 2 sin e 2 sin e 2 1 222 D D 1 22

An object of height 2 cm is placed at a distanc 20 cm in front of a concave mirror of focal length 12 cm Find the position size and nature of the Ans 30 cm in front of mirror 3 cm image high real inverted and magnified

In Young s double slit experiment the y coordinates of central maxima and 10th maxima are 2cm and 8cm respectively When the YDSE apparatus is immersed in a liquid of refractive index 1 5 the corresponding y coordinates will be A 2cm 4cm C 2cm 6cm B 3cm 6cm D 4 3cm 16 3cm

If an object is placed at a distance of 30 cm from a lens a virtual image is formed If the magnification of the image is find the position of the image and the focal length of the lens Also find the nature of the lens 3

A person wears eye glasses with power of 5 5 D for distance viewing His doctor prescribes a remedy of 1 5 D for his near vision What should be the focal length of extra lens which should be pasted over lower section of his eyeglasses for correct near vision 12 5 cm 14 3 cm 16 7 cm 19 3 cm

In case of a prism red light bends the le ast whereas in the case case of raindro p red light will have greater angle of dev iation i e after refraction partial internal reflect and reflect inside the raindrop Am I right

ALLEN An air bubble is inside water The refractive 4 index of water is 4 3 At what distance from the air bubble should a point object be placed so as to form a real image at the same distance from the bubble 1 2R 2 3R 3 4R 4 The air bubble cannot form a real image gegen utan ada 4 3 18 aggage cu va face and then af fffa fafara gera 1 2R 2 3R 3 4R 4 gergea anafafafara

The focal length of eyepiece and objective lens of astronomical telescope are 2 5 cm and 50 cm respectively Then maximum angular magnificati will be O 20 O 22 0 1 O 220

A large concave mirror with a radius of curvature of 0 5 m is placed on a horizontal plate We pour a small amount of water into the mirror and place on it a plano convex lens with a radius of curvature of 1 0 m whose plane side just covers the water Then we place a point light source above this set up at a height of 0 3 m The distance in metres between the object and the final image formed will be x 90 Find x given that the refractive index of water is 4 3 and the refractive index of glass is 1 50

An astronomical telescope has magnification having magnitude 5 for distance objects The separation between objective and eye piece is 36 cm and final image is formed a infinity The focal lengths of objective and eye piece are 22 cm 14 cm 30 cm 6 cm 24 cm 12 cm 32 cm 4 cm

A ball is projected along the principal axis with speed 10 2 m s at an angle of 45 with the principal axis of a concave mirror If the ball is at 10 m beyond the centre of curvature at the time of projection then relative speed of the image with respect to the object when it crosses the centre of curvature will be 10 2 m s 45 10 m C F P f 15 cm X

An object of height 1 cm is placed perpendicularly to the principal axis of a concave mirror of focal length 10 cm at a distance of 10 m from it The height of the image formed by the mirror is 1 0 1 mm 2 1 mm 3 2 mm 4 4 mm

A wall is moving with velocity u and a source of sound moves with velocity in the same direction as shown in the figure Assuming that the sound travels with ve 2 10u If the ratio of incident sound wavelength on the wall to the reflected sound wavelength by the wall is a b Find a b u

A hemispherical glass paper weight of radius 10 cm contains a small air bubble located at a distance of 4 cm from its flat surface on its axis of symmetry What is apparent shift in the position of air bubble when it is looked by observer from top 4 Refractive index of glass 3

A plano convex lens when silvered in the plane side behaves like a concave mirror of focal length 30cm However when silvered on the convex side it behaves like concave mirror of focal length 10 cm Then the refractive index of its material will be

It is once suggested that the mirror for an astronomical telescope could be produced by rotating mercury in a container at a prescribed angular velocity about a vertical axis With what angular velocity in rad sed the disk be rotated to produced a 10 cm focal length mirror Give answer in nearest integer

37 Find the apparent depth of an object O placed at the bottom of a beaker as shown in which two tingeetquestoayers of transparent liquids are filled ace it s e is h 25cm h 15cm 1 20cm O P 1 5 H 2 5 2 24 60cm AA A

12 Huygens principle of secondary wavelets may not be used to 1 Find the new position of a wavefront 2 Explain Snell s law 3 Explain laws of reflection 4 Explain particle behaviour of light 13 It is found that when waves from two identical coherent sources superpose at certain point with same individual intensity then the resultant intensity is equal to the intensity of one wave only This means that phase difference between the two waves at that point is 1 Zero 3 27 3 14 Two slits are separated by a distance of 1 mm are illuminated with red light of wavelength 6 5 x 10 7 metre The interference fringes are observed on a screen placed 1 metre away from the slits The distance between 3rd dark fringe and fifth bright fringe is equal to 1 0 65 mm 3 3 23 m 3 2 1 63 mm 4 4 68 mm 15 When a thin transparent plate of thickness t and refractive index u is placed in the path of one of 2 T 3 4 1 t 2 1 t 4 ut 16 The minimum thickness of a soap bubble film u 1 33 that results in constructive interference in the reflected light if the film is illuminated with light whose wavelength in free space is 600 nm is 1 112 50 nm 3 400 nm 1 0 36 3 0 72 two interfering beam of light the centestioner between two waves at the position central is 1 1 t 2 225 26 nm 4 176 5 nm 17 The light of wavelength 6328A is incident on a slit of width 0 2 mm perpendicularly the angular fringe width of central maxima will be 2 0 18 4 0 09 1 18 The diameter of the objective of a telescope is a its magnifying power is m and wavelength of light is A The resolving power of the telescope is 1 22 a Am 1 22a 3 19 A beam of unpolarised light passes through a tourmaline crystal A and then it passes through a second tourmaline crystal B oriented so that its principal is parallel to that of A The intensity of the emergent light is Now B is rotated by 45 about the ray The emergent light have intensity 1 1 1 202 3 9 2 4 2 2 3 20 In Young s double slit experiment interference pattern is found to have an intensity ratio between bright and dark fringes as 9 Then amplitude ratio of the wave reaching the screen from two sources is 3 a 1 22 a 1 22 m 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 400mm 2 525mm 4 547mm 3 642mm 22 A soap bubble 250nm thick is illuminated by white light The index of refraction of the soap bubble is 1 36 Which wavelength is missing in range of visible light for reflected rays 1 300mm 3 400mm 2 2 4 3 23 Maximum distance from diffraction slit of slit width a upto which ray optics holds for wavelength is 2 600mm 4 680nm N E

1 1 3 3 3 2 2 2 3 4 3 1 17 A plano convex lens of refractive index 1 5 and radius of curvature 30cm is silvered at the curved surface Now this lens has been used to form the image of an object At what distance from this lens an object be placed in order to have a real image of the size of the object 1 20 cm 3 60 cm 2 30 cm 4 80 cm

10 In a compound microscope the lateral magnifications of objective lens is 5 and magnifying power of eyepiece is 2 then magnifying power for compound microscope for normal adjustment will be 1 2 5 2 10 4 5 3 2

9 If the size of an image formed by a convex mirror of focal length fem is 1 nth of the size of the object then calculate the distance of the object from the mirror when n 1 Ans n 1 fcm

3 3 2 59 In a compound microscope the intermediate image formed is 4 1 Virtual erect and magnified 2 Real inverted and diminished 3 Virtual erect and diminished

Aakash Institute 0 An astronomical telescope is to be designed to have a magnifying power of 50 in normal adjustment If the length of the tube is 102 cm then power of the objective and the eyepiece respectively is 1 1D 40D 3 50D 1D 2 1D 50D 4 2D 50D

m 1 1 1 39 A compound microscope has a magnifying power of 400 when the image is formed at infinity The objective has a focal length of 0 5 cm and the tube length is 18 cm The focal length of eye piece is Normal near point is 25 cm 1 5 5 cm 2 9 5 cm 3 15 5 cm 4 2 25 cm

34 A ray of light incident at an angle 8 on the refractingeetde face of a prism emerges from the other face normally If angle of the prism is 5 and it s refractive index is 1 5 the angle of incidence is nearly 1 7 5 2 5 3 15 4 2 5 35 What should be the maximum value of 0 such that 38

distance D capable of screen will separated D f Ray Optics and Optical uments 27 In an astronomical telescope using objective and eyepiece of focal length 50cm and 5cm length of telescope obtained is 54 5cm when the final image of a star was at distance x cm from the eyepiece Find x 1 35 3 25 2 45 4 15

The length of an astronomical telescope adjusted for parallel light is 90 cm If the magnifying power of the telescope is 17 then the focal length of eyepiece and objective are respectively 1 10 cm and 80 cm 2 85 cm and 5 cm 3 70 cm and 20 cm 4 5 cm and 85 cm

A far sighted person can see object beyond 49 cm clearly If separation between glasses and eye len is 1 cm then find focal length of glass 1 30 cm 2 25 cm 3 24 cm 4 48 cm