Optical Instruments Questions and Answers

For a right angled prism PQR immersed in water the incident and emergent rays are parallel as shown in figure The minimum value of refractive index of the prism is 3 A C 3 4 B D P Incident ray Emergent A point object O is placed between two plane mirrors as shown in M 10mm M

A 15 cm tall object is placed 25 cm away from a CONVERGING LENS with a focal length of 15 c paper Draw all 3 rays that were studied in Lecture Ray 1 Ray 2 and Ray 3 Use arrows to re Magnified or Reduced Based on your Ray Diagram the image is O Real Inverted and Reduced O Real Erect and Magnified O Virtual Erect and Magnified Virtual Erect and Reduced O Real Erect and Reduced O Virtual Inverted and Magnified O Virtual Inverted and Reduced Real Inverted and Magnified

A ember The incident ray reflected ray and the outward drawn normal are denoted by the unit vecto A2 b and respectively Then choose the correct relation for these vectors 1 2 b 2 c c 3 h 2 b a 2c b a c 4 10

instrument tration 20 What is the diameter of sphere shown in figure Pitch of screwgauge is 1 mm and number of divisions in circular scale are 50 1 238 cm 10 HICHE 2 1 218 cm 3 1 228 cm 1 20 bulundu 15 10 0 cm 4 1 215 cm

28 If the lower half of a concave mirror s reflecting surface is made opaque which of the following statements describe the image of an object placed in front of the mirror S1 Intensity of the image will increase S2 The image will show only half of the object S3 No change in the image S4 Intensity of the image will be reduced to half a S1 only b S2 only c S2 and S3 d S4 only AMU Med

42 Fig 4 1 is a ray diagram representing two rays passing through a converging lens A Fig 4 1 a State which of the labelled points is a principal focus of the lens b State which of the distances BX XY YZ or XZ is the focal length of the lens 1 1 c On Fig 4 1 draw another ray from point A to locate the image of point A Label this image I 3 d On the ray diagram in Fig 4 1 the refraction is shown occurring at the centre line of the lens State where the refraction actually occurs

25 The maximum number of possible interference maxima for slit separation equal to 2 5 times the wavelength in Young s double slit experiment is 1 Infinite 3 Three 2 Five 4 Zero

Parallel beam the screen screen incident on a thin lens u 1 4 and radii 25 cm of each of the surfaces as shown What should be the thickness of a slab in cm u 1 5 between the lens and the screen so that final image is formed on 35 cm

llustration 20 A magnifying lens has a focal length of 10 cm a Where should an object be placed if the image is to be 30 cm away from the lens b What will be the magnification Solution a b In case of magnifying lens it is convergent in nature and the image is erect enlarged virtual between infinity and object and on the same side of the lens f 10 cm v 30 cm m and hence from lens formula 1 1 1 we have i e u 7 5 cm 30 u 10 So the object must be placed at a distance of 7 5 cm which is f in front of the lens h V 30 7 5 and 1 1 1 vuf u h 1 4 i e image is erect virtual and four times the ri 30cm U

a simple e placed 1 The ximum nt cm micro X for a or ver for a 25 cm is observer reads a book with small print using a magnifying glass a with normal near point 25 cm thin convex lens of focal length 5 cm the eye ens and i What is the closest and the farthest distance at which he can read the book when viewing through the magnifying glass ii What is the maximum and the minimum angular magnification magnifying power possible using the above simple microscope NCERT Solution i For the closest distance v 25 cm f 5 cm u As 1 1 or u V U f 1 1 1 U 1 1 1 vf 25 5 25 6 U This is the closest distance at which the man can read the book For the farthest image V f 5 cm 1 V f cm 4 2 cm 1 1 5 6 25 25 u 1 5 0 25 min 25 6 Minimum angular magnification 11 u 5 cm This is the farthest distance at which the man can read the book ii Maximum angular magnification D 6 1 1 5 5 HD 14355

A glass cylindrical vessel with base concave mirror of focal length 20 cm is filled with two immiscible liquid of refractive index 1 5 and 1 4 Thickness of liquid level are 15 cm and 14 cm respectively A fish is moving vertically upward along principle axis of mirror with speed of 1 cm s A bird is moving along vertically downward direction with 2 cm s A small hole is made at bottom surface of vessel When distance of fish from pole of mirror is 10 cm the rate of liquid level falling is 1 cm s focal length of concave mirror is 20 cm Then at the given instant 1 cm s 14 cm 1 cm s 15 cm 2 cm s u 1 4 u 1 5 Bird E cm s Fish 10 cm f 20 cm A Velocity of image of fish formed after reflection from mirror as seen by bird is 1 cm s alor upward direction B Velocity of image of fish after formed after reflection of mirror as seen by bird is 1 cm s al downward direction C Velocity of image of fish as seen by itself is 5 cm s along downward direction D Velocity of image of fish as seen by itself is 5 cm s along vertically upward direction

PHYSICS XII roblems For Practice 1 A convex lens of focal length 25 cm is placed coaxially in contact with a concave lens of focal length 20 cm Determine the power of the combination Will the system be converging or diverging in nature CBSE D 13 Ans ID diverging 2 A conves lens of focal length 20 cm is placed coaxially in contact with a concave lens of focal length 25 cm Determine the power of the combination Will the system be converging or diverging in nature CBSE D 13 Ans ID converging 3 The radius of curvature of each surface of a convex lens of refractive index 1 5 is 40 cm Calculate its power Ans 2 5 DI 4 Two lenses of powers 10 D and 5D are placed in contact Calculate the power of the new lens Where should an object be held from the lens so as to obtain a virtual image of magnification 27 CBSE OD 08 Ans 5D 10 cm Find the focal length and power of a convex lens which when placed in contact with a concave lens of focal length 25 cm forms a real image 5 times the size of the object placed 20 can from the combination Ans 10 cm 10 D 6 The power of a thin convex lens of glass is 5 D When it is immersed in a liquid of refractive index s it behaves like a divergent lens of focal length 1 m Calculate u of liquid if u of glass 3 2 Am 5 3 7 A compound lens is made of two lenses having powers 15 5D and 55D An object of 3 cm height is placed at a distance of 30 cm from this compound lens Find the size of the image Aru 1 5cm 8 Rays coming from an object situated at infinity fall on a convex lens and an image is formed at a distance of 16 cm from the lens When a concave lens is kept in contact with the convex lens the image is formed at a distance of 20 cm from the lens combination Calculate the focal length of the concave lens Ans 80 cm An equiconvex lens with radii of curvature of magnitude 20 cm each is put over a liquid layer poured on top of a plane mirror A small needle with its tip on the principal axis of the lens is moved along the axis until its inverted real image coincides with the needle itself The distance of the needle from the lens is measured to be 30 cm On removing the liquid layer and repeating the experiment the distance is measured to be 20 cm HINTS LP R 6 Given that the two values of the distance measured represent the focal length values in the two ce calculate the refractive index of the liquid Ans 133 CBSE D 0SC 100 100 25 20 As the power of the combination is negative the system will be diverging in nature 2 Power of convex lensu 100 20 Power of concave lens P Power of the combination P R ID As the power Pis positive the combination will be converging in nature 3 Here 15 40 cm 0 40 m R 40cm 0 40 m P 7 2 15 1 Now 1 1 0 40 0 40 4 P R P 10 5 5D or De 100 cm cm 1 ii m 20 cm As m 20 20 5 Here m 5 20 cm As 2 M 4 5 1D 5 6 01 5 1 H or 20 1 1 1 3 1 50 or 100 25 2 5 D 50 u 10 cm 5D com 4D 1 3 2 1 25 50 10 100 10 cm and P 10 10 D

A person wishes to distinguish between two pillars located at a distance of 11 km What should be the minimum distance between these pillars Question Type Single Correct Type 1 1 m 2 3 m 3 0 5 m A 5 m

A particle strikes elastically with another stationary particle with velocity V After collision it moves with half the velocity in the same direction Find the velocity of the second particle after collision Question Type Single Correct Type 1 2 3V 2 V 2 3 V

5 A uniform wire frame of linear mass density having three sides each of length 2a is kept on a smooth horizontal surface An impulse J is applied at one end as shown in the figure P is the midpoint of AB Now answer the following question 3 J 222a B 3J 112 a X The angular velocity of system just after the impulse J A C 112a A B j 62a P The velocity of point P just after the impulse is A j C i 1 a 11 B D 2J 112a D 11 i j

A light ray travelling in glass medium is glass air interface at an angle of indcidence 0 The reflected R and transmitted 7 intensities both as function of 0 are plotted The correct sketch is 1 100 Intensity 2 100 Intensity 3 100 Intensity 4 100 Intensity 0 T R T R T R T R 0 90 0 90 0 90 LALAA

A short linear object of length b lies along the axis of a concave mirror of focal length fat a distance u from the pole of the mirror The size of the image is approximately equal to 1 2 1 2 f f c b u f a b U b b d b f u f 2 4 f

The graph shows how the reciprocal of magnification produced by a converging thin lens varied with object distance u in displacement method What was the focal length of the lens used 1 2 Question Type Single Correct Type a b a bc a C u

A ray of light travels in the way as shown in the figure After passing through water the ray grazes along the water air interface The value of g in terms of i is Glass 1 sin i 3 4sin i 4 3 sini Komed T 3 water

A real image of a distant object is formed by a plano convex lens on its principal axis Spherical aberration 1998 2M a is absent b is smaller if the curved surface of the lens faces the object c is smaller if the plane surface of the lens faces the object d is the same whichever side of the lens faces the object

D When light of wavelength is incident on an equilateral prism kept in its minimum deviation position it is found that the angle of deviation equals the angle of prism itself The refractive index of the material of the prism for the wavelength is 1 3 3 2 m m 2 3 2 4 2

125 The length of the tube of a microscope is 10 cm The focal lengths of the objective and eye lenses are 0 5 cm and 1 0 cm The magnifying power of the microscope is about a 5 b 23 c 166 126 Th 0 d 500 ith

In an interference arrangement similar to Young s double slit experiment the slits S and S are illuminated with coherent microwave sources each of frequency 106 Hz The sources are synchronized to have zero phase difference The slits are separated by a distance d 150 0 m The intensity I 0 is measured as a function of 0 where 0 is defined as shown If I is the maximum intensity then I 0 for 0 0 90 is given by 1995S a I 0 10 2 for 0 30 b I 0 1 4 for 0 90 d 2 c I 0 Io for 0 0 d I 0 is constant for all d 2 S S 50

The far point of a near sighted person is 6 0 m from her eyes and she wears contacts that enable her to see distant objects clearly A tree is 18 0 m away and 2 0 m high a When she looks through the contacts at the tree what is its image distance b How high is the image formed by the contacts

The real image of an object is formed at a distance of 90 cm from a concave mirror of focal length 15 cm The magnification of the object is Ich dea che altafach ufaf 15 cm ch 90 cm A 5 Affa sta zi

A biconvex lens of focal length 15 cm is in front of a plane mirror The distance between the lens and the mirror is 10 cm A small object is kept at a distance of 30 cm from the lens The final image is 1 Virtual and at a distance of 16 cm from the mirror 2 Real and at a distance of 16 cm from the mirror 3 Virtual and at a distance of 20 cm from the mirror 4 Real and at a distance of 20 cm from the mirror

12 In the Foucault s experiment the distance between the concave mirror and plane mirror is 4000 metre and the plane mirror is rotating with 36 x 103 revolutions per minute Calculate the velocity light if the mirror rotates through 5 8 Ans 2 98 x 108 m sec

A nano photonic device makes a beam of around 10 unpolar ized photons incident on polarizer analyzer system If a photon counter detects around 2500 photons transmitted by the analyzer then the number of photons blocked by the polarizer analyzer system and the angle between polarizer analyzer axes must be respectively 7500 and 45 degree 7500 and 60 degree 5000 and 30 degree 2500 and 45 degree

What is principal quantum number of the highest energy level for which the lines in the Balmer series of emission spectra of atomic hydrogen will just be resolved by a spectrometer of resolving power d 8 10 a 30 c 50 b 40 d 60

At a point on the screen in YDSE experiment 3rd maxima is observed at t 0 Now screen is slowly moved with constant speed away from the slits in such a way that the centre of slits and centre of screen lie on same line always and at t 1 sec the intensity at that point is observed 3 4 th of maximum intensity in between 2nd and 3rd maxima The speed of screen will be D separation between the screen and slits d separation between the slits d D 5000A 13D 5 A 6 5D 13 17D 5 B 17

A ray of light incident at an angle q on a refracting face of a prism emerges from the other face normally If the angle of the prism is 5 and the prism is made of a material of refractive index 1 5 what is the angle of incidence

having the same speed are used instead of electrons then the resolving power of scanning proton microscope will be changed by a factor of 1 1837 1837 B 1837 1 1837 1 Question Type MCQ Question ID 8612511

if a len is cut vertically into two equal halves then the intensity of transmitted light and aperture of the lens O half half respectively O remains same O half double respectively O double half respectively

te Motion Obiora s walk is traced by a GPS map she walks 25 0 m in a direction of 45 0 below horizontal to reach point A She continues at point A and walks 40 0 m in a direction of 60 0 above horizontal to reach point B a On a 2D coordinate system draw the resultant vector d as Obiora s total displacement as she reaches point B b Find the vector component form of the vector d NOTE d d dy What is d and dy c Find the magnitude and direction of the vector d

The image of the moon is focussed by a converging lens of focal length 50 cm on a plane screen The image is seen by an unaided eye from a distance of 25 cm Find the angular magnification achieved due to the converging lens

Example 9 6 A point source of light S placed at a distance L in front of the centre of a mirror of width d hangs vertically on a wall A man walks in front of the mirror along a line parallel to the mirror at a distance 2L from it as shown Find the greatest distance over which he can see the image of the light source in the mirror d S

A man uses a concave mirror for shaving He keeps his face at a distance of 25 cm from the mirror and gets an image which is 14 times enlarged Find the focal length of the mirror

1 2 Three polaroid sheets P P2 and P3 are kept parallel to each other such that the angle between pass axes of P and P is 45 and that between P and P3 is 45 If unpolarised beam of light of intensity 128 Wm 2 is incident on P What is the intensity of light coming out of P3 W A 64 Wm 2 B 128 Wm 2 C 0 D 16 Wm 2

A prism is made of glass of refractive index 1 5 If t angle of minimum deviation is equal to the refracti angle of the prism calculate the angle of the prism

An astronomical telescope in normal adjustment receives light from a distant source S The tube length is now decreased slightly then 1 A virtual image of S will be formed at a finite distance 2 No image will be formed 3 A small real image of S will be formed behind the eyepiece and close to it 4 A large real image of S will be formed behind the eveniece and far away from it

Three charges q 1 10 6 q 2 10 6 q3 3 10 6C have been placed as shown in figure in four surfaces S S S and S electrical flux emitted from the surface S in N m2 C will be 1 36 x 10 2 36T X 10 ap 3 36p 10 4 36p 108

A marginal ray falls upon a concave mirror of radius of curvature 20 cm as shown in figure Find distance CM in cm 1 10 3 20 30 M 2 16 4 10 3

i the instantaneous current I ii instantaneous L power P ii the frequency of power and iv the maximum energy stored in the capacitor 30 Draw a ray diagram to show the image formation in a refracting type astronomical telescope when the final image is formed at infinity Write down the expression for its magnifying power Why should the diameter of the objective of telescope be larger

An optical fibre is used for data transmission at high frequency If refractive index of core and cladding are respectively then angle of acceptance is 1 sin 1 2 1 3 sin 2 cos 1 1 4 cos H H

along the diameter into two identical halves In this process a layer of the lens t in thickness is lost then the halves are put together to form a composite lens In between the focal plane and the composite lens a narrow slit is placed near the focal plane The slit is 26 emitting monochromatic light with wavelength 2 Behind the lens a screen is located at a distance L from it S 23 A d S K S u f V 1 L K D Find the fringe width for the pattern obtained under given arrangement on the T 2

A small object is placed 20 cm in front of a cube of glass of 10 cm edge and its farther side is silvered The image is formed 22 cm behind the silver face The refractive index of the glass cube is 1 1 22 3 1 67 2 1 42 4 1 72

A concave lens having a focal length of 10 cm in air is placed in water Its focal length in water will be given 1 33 Hg 1 5 a 28 cm c 39 cm b 10 cm d 15 cm

A square ring laser interferometer can be used to measure small vibrations in the earth by sending one laser beam clockwise around the square and one laser beam anti clockwise around the square bouncing off mirrors at the corners see figure 3 They interfere at the opposite corner to where they are produced The detection limit is set by the interference pattern changing from constructive to destructive Laser light is produced Laser light interferes Figure 3 Schematic for question part c i If the lasers used have a wavelength of 520 nm what is the minimum length distortion the ring laser can measure ii Describe how a coating could be applied to one of the mirrors so at rest the interference is destructive interference 2

A convergent lens has a focal length of 13 5 cm The object distance is 25 2 cm P h h Answer in units of cm Scale 10 cm Find the distance of the image from the center of the lens Answer in units of cm 9 part 2 of 2 Find the magnification Your response

Consider a concave mirror with radius R An upright object is placed between the in R terval and R The image is R 2 1 real upright reduced 2 virtual inverted reduced 3 virtual upright reduced 4 real upright same size 5 virtual inverted enlarged 6 real inverted reduced O 7 virtual upright same size 8 virtual upright enlarged 9 real upright enlarged 10 real inverted enlarged