Optical Instruments Questions and Answers

A convex lens is painted black at the edge symmetrically This lens will form the complete image of an object The brightness of the image will be less than the image formed by the original len The focal length of the lens will decreases Both 1 2

A convex lens and a concave mirror having equal focal length are placed at a distance d apart A point source of light is placed at a distance of 2f from the lens on the other side The seperation between lens and mirror is in such a way that final image of the source is on the source itself The value of d is 1 2f 2 4f 3 f 4 both 1 and 2 are possible

The current sensitivity of a moving coil galvanometer is 5 div mA and its voltage sensitivity angular deflection per unit voltage applied is 20 div V The resistance of the galvanometer is 1 40 12 2 25 2 A

An astronomical refracting telescope will have large angular magnification and high angular resolution when it has an objective lens of 1 small focal length and large diameter 2 large focal length and small diameter 3 large focal length and large diameter

A prism is made of glass of unknown refractive index A parallel beam of light is incident on a face of the prism The angle of minimum deviation is measured to be 40 What is the refractive index of the material of the prism The refracting angle of the prism is 60 If the prism is placed in water refractive index 1 33 predict the new angle of minimum deviation of a parallel beam of light of

horizontally along X axis as shown in the figure A ray given by 3Z X 10 space for rough work Page 13 is incident at a point P on face AB of the prism The value of u for which the ray grazes the face AC is Z

Minimum separation of two points seen as distinct by a compound microscope is is refractive index of medium and is wavelength of light dmin dmin dmin 1 22 cos 1 22 A 2 sin 0 61 sin

Physics A ray of light propagates a distance L in vacuum Then a glass plate with thickness d L and index of refraction n 1 is inserted in the path of the ray a Calculate the phase difference between the fields in these two cases after propagation b Calculate then an approximation serial expansion for the field in the latter case when the thickness of the glass plate d is extremely small c The result is a superposition of the incident field and the field scattered by the plate What is the phase differen theo w field hotu

A point object in air is in front of the curved surface of a plano convex lens The radius of curvature of the curved surface is 30 cm and the refractive index of the lens material is 1 5 then the focal length of the lens in cm is

A liquid of refractive index 1 33 is placed between two identical plano convex lenses with refractive index 1 50 Two possible arrangement P and Q are shown The system is P Q 1 Divergent in P convergent in Q 2 Convergent in P divergent in Q 3 Convergent in both 4 Divergent in both

The diameter of moon is 3 5 10 km and its distance from the earth is 3 8 x 10 km If it is seen through a telescope whose focal length for objective and eye lens are 4 m and 10 cm respectively then the angle subtended by the moon on the eye will be approximately a 15 b 20 c 30 d 35

There are two sources kept at distances 22 A large screen is perpendicular to line joining the sources Number of maximas on the screen in this case is 2 wavelength of light dh TES S 22 b se o 5 irall 5 8 0 7

If a film having suitable thickness d with a refractive index less than that of glass is coated on the glass then waves reflected from the upper surface of the film interferes destructively with the waves reflected from the lower surface of the film Such a film is called non reflecting film Let na nf and ng be the refractive index of air reflecting film and glass respectively Select the correct alternative A is the wavelength of light in air 1 2 3 Question Type Multiple Correct Type d d X 4nf 3 4 X 2 2n 1 Air n 1 Nonreflecting film n n Glass n x 0 n x d For complete destructive interference nang when n nf na nf

e e B e All questions are compulsory Section A 1 to 11is very short answer questions and carries 1 mark each Section B 12 to 18 are short answer questions and carry 2 marks each Section C 19 to 23 are long answer questions and carry 3 marks each Section D 24 to 25 are long answer questions and carry 5 marks each 1 The power of a thin convex lens of glass is 5 D When it is immersed in a liquid then it behaves like a divergent focal length 100 cm The refractive index of the liquid is Given refractive index of glass 1 5 a 3 5 b 1 2 c 2 3

SECTION B 11 An object of size 3 0 cm is placed 14 cm in front of a concave lens of focal length 21 cm Describe the image produc by the lens What happens if the object is moved further away from the lens 12 What is the focal length of a convex lens of focal length 30 cm in contact with a concave lens of focal length 20 cm

When an astronomical telescope is adjusted for parallel rays the distance of objective from the eye piece is found to be 1 05 m The magnifying power of telescope is 20 The focal length of eyepiece lens is 01m O 0 05 m O 0 95 m 0 52 m

Question Type Fill in the blanks A A Question No 4 Negative Marks in all other cases A parallel light beam falls on a lens which is silvered from back side as shown and both surfaces have radius 25 cm then distance in cm from lens where the beam converges 16x on principle axis is x so fill value of 25

A block of mass 4kg is moving with a velocity of 7 m sec on a surface It collides with another block of mass 3 kg elastically The surface is smooth for 4 kg block but rough for 3kg block p 0 2 Find the time in sec after which next collision will occur g 10 m s

Q26 A biconvex thin lens of radius of curvature R is made up of variable refractive index P 2 11 Assume very small aperture 2d R A point object O is placed at a distance R 7 5 m on the principal axis from the lens as shown Due to variable refractive index of lens there are infinite numbers of images on the principal axis These images are spread over the length Find the value of in m RVRY Review Later

1 Define angle of prism and derive an expression for angle of prism in terms of refracting angle i e A r 4 1 ii How are we able to see nearby and also the distant object clearly OR i A person needs a lens of power 2 D for correction of her vision What kind of defect in vision she is suffering from What is the nature and focal length of the corrective lens 3 ii What is the horizontal field of view with one eye and with two eyes 2 How is Plaster of Paris prepared Write two properties and two uses of Plaster of Paris Also write the balanced chemical equation s involved 1 2 2 i Do plants have nervous system Yes or No Justify your answer by giving an example of pea plant 3 ii Name any four plant hormones 2 2 ash dations

23 Three charges q q and q are placed at the corners of an equilateral triangle of side a The resultant electric force on a charge q placed at the centre of the triangle is 1 3 1 4T Eo 30 a 1 3 30 2 a ro 2 1 30 41 EU 4 Zero

Lens maker formula Power of lens Silvering of lens A thin convex lens of focal length 20 cm is kept in contact with a plane mirror The focal length of the combination will be 1 5 cm 3 20 cm 2 10 cm 4 Infinite

6 The maximum intensity in Young s double slit experiment is Io What will be the intensity of light in front of one of the slits on a screen where path 2 difference is Lay To 2 c b 10 6 10 d 11

1 Two point charges of magnitude 1 0nC and 3 0nC are respectively located at a distance of 2 0 cm and 4 0 cm from the origin on the positive x axis The total force exerted by these two charges on a charge of 5 0nC located at the origin is A 196 C towards x axis C 28 C towards x axis B 196 C towards x axis D 28uC towards x axis

place e A thin lens made of glass refractive index 1 5 of focal length f in air is immersed in a liquid of refractive index 4 3 If its focal length in liquid is f then the ratio fit Answer

A medium bounded by the planes x 0 x a y b y b z c and z 0 has refractive index x z Az Bx 2 A ray of light traveling along positive z axis enters the medium at point P 1 B 0 Then the optical path introduced by the medium when the light ray emerges out will be Ac 4 A C 2c B 4Ac D Ba 2

Two slits are separated by 0 3 mm A beam of 500 nm light strikes the slits producing an interference pattern The number of maxima observed in the angular range 30 0 30 1 300 2 150 3 599 4 601 H 10

contains 800 cm of water A cylindrical glass piece of diameter 8 0 cm and height 8 0 cm is placed in the vessel If the bottom of the vessel under the glass piece is seen by the paraxial rays see figure locate its image from bottom The index of refraction of glass is 1 50 and that of water is 1 33 48 cm

The two loops shown in the figure have their planes parallel to each other A clockwise current flows in the loop X as viewed from X towards Y The two coils will repel each other if the current in the loop X is o o X

35 Two neighbouring coils A and B have a mutual inductance of 20 mH The current flowing through A is given by i 3 4t 6 The induced emf at t 2s is 1 160 mV Mate 3 260my 2 200 mV LAY 300 ml

A convex lens made of glass of refractive index 1 5 has focal length 10 cm in air It is taken inside a transparent liquid of refractive index 1 2 Find its focal length in the liquid 40 cm 30 cm 20 cm 10 cm

30 A point isotropic light source of power P 12 watts is located on the axis of a circular mirror of radius R 3 cm If distance of source from the centre of mirror is a 39 cm and reflection coefficient of mirror is a 0 70 then the force exerted by light ray on the mirror is 10 0 N

A thin convex lens whose focal length in air is known to be 30 cm is cut into two parts by a transverse plane parallel 0 5 cm to the principal axis and 0 5 cm above the principal axis They are placed on the x axis as shown in the figure A point object is placed at the origin of a coordinate system Find the separation in m between two final images formed due to the rays which get retracted by both the parts of lens assuming paraxial ray approximations to be valid A Origin 0 0 45 0 105 0

A ray of light is incident on a concave mirror It is parallel to the principal axis and its height from principal axis is equal to the focal length of the mirror The ratio of the distance of point B from centre of curvature to the distance of the focus from the centre of curvature 1 7 3 2 WIN N W WIN 3 TA B

Consider the shown arrangement of a plane mirror and a concave mirror f 20 cm placed at distance of 50 cm as shown If a point object S is placed in between then numerical value of Y coordinate of image formed by plane mirror consider 1st reflection from concave mirror and then by plane mirror is found to be 5N cm Find N 45 20 cm S 30 cm fM 20 cm MENEN 27

0 In a Young s double slit experiment a light of wavelength 500 nm falls on it Its slits separation is 2 mm and distance between plane of slits and screen is 2 m then find distance of a point on the screen from central maxima where intensity becomes 50 of central maxima a 1000 m c 250 m b 500 m d 125 m 2019

A point source of light is placed directly above an opaque sphere of radius y placed on a horizontal surface For x Point source Horizontal surface 2y For x 24 2y 3 radius of shadow formed on horizontal surface is 2y For x y radius of the shadow formed on horizontal surface is 3y and for surrounding medium havin refractive index 3 radius of shadow forme on horizontal surface is 2y For x y and for surrounding medium having refractive index 3 radius of the shadow formed on horizontal surface is

Two spherical mirror one of convex and other concave each of same radius of curvature R are arranged coaxially at a distance 2R from each other A small circle of radius a is drawn on the convex mirror near the pole as shown in figure The radii of 3rd image taking the first reflection at the concave mirror then the successive reflection at the convex mirror and finally the third successive reflection at concave a mirror again of the circle is then value of x is 40 X M 2R

A point source of light S is placed in front of a large screen at a distance of 100 unit from the screen as shown Intensity at a point P on the screen point P is the point on screen closest to source S is S 100 Screen P Choose the correct answer 1 A large mirror is now placed at a distance of 50 unit from the source S towards the left of source S as shown New intensity of light at Pis 1 only 2 1 25 3 1 5 4 2 50 S 100 P Screen

A concave lens has a focal length of 0 5 m When combined with a second lens the combination has a power of 0 5D Which of the following could be the second lens A Concave lens of focal length 1 m B Convex lens of focal length 40 cm C Concave lens of focal length 40 cm D Convex lens of focal length 2 m

2 8 A convex lens made of 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 1 converging lens of focal length 10 cm 2 diverging lens of focal length 10 cm 3 converging lens of focal length 10 3 cm 4 diverging lens of focal length 30 cm that

Particle of mass m placed on a horizontal surface surrounded by walls as shown in figure Coefficients of restitution for collision with walls AB BC CD are e 1 e 1 2 e 1 4 respectively Particle 1st collide with AB as shown After collision from wall BC CD respectively if again return to same position Relation between 81 82 8 will be AM B tan 8 2 tan 8 tan 6 2 tan 8 tan 8 2 cot 8 4 cot 8 tan 6 m u 8

To realize the given truth table from the circuit shown in the figure the input to J in terms of A and B would be have to be A o Bo A 0 0 1 Combinational Logic Circuit B 0 1 0 clk Qn 1 Qn 1 Qn 0 J K Q

0 A telescope can resolve two points 500 m apart on moon If the diameter of the telescope is doubled the minimum distance between two points on moon which can be just resolved is 1 1000 m 2 500 m 3 250 m 4 125 m M proa of cross section A and density D is floating on surface of water If it

A screen is placed at a distance of 40 cm away from an illuminated object A converging lens is placed between the source and screen and it is attempted to form the image of the source on the screen If no lens position could be found the focal length of the lens INCERI rg 1 Should be greater than 10 cm 2 May be 6 cm 3 May be infinity 10 cm

A plane mirror is placed along the verti cal plane yz plane If a particle is also projected in the vertical plane with spee d of projection 10 m s and angle of proj ection as 60 from the normal direction to mirror The point of projection is at a distance of 5m from the mirror and the particle is d irected towards the mirror The magnitu de of velocity of approach of particle a nd image just before the particle touch es the mirror is 10 m s 60

lens is kept between them so that a real image is formed on the screen for two different positions of the lens Difference between the positions of the lens is 60 cm The focal length of the lens is 1 22 5 cm 2 45 cm 3 20 cm 4 20 5 cm fffffaa fefe 60 cm 30 31 1 22 5 cm 2 45 cm 3 20 cm 4 20 5 cm

2 30 3 45 4 90 Grazing incidence 9 The diameter of aperture of an astronomical telescope is 9 1 22 m What should be minimum separation between two objects at distance 10 km from the telescope to observe them distinctly take wavelength of light to be 5000 1 2 m 2 50 cm 3 5 mm 4 5 cm 2 30 3 45 4 90 Grazing incidence rinda qal ara a1 22 m 110 km 14 fy fand e az 5000 1 2 m 3 5 mm 2 4 5 cm 50 cm

3 An object P is placed at a distance of 15cm from a convex lens of focal length 10cm On the other side of the lens a convex mirror is placed at its focus such that the final image formed by the combination coincides with the object itself The focal length of convex mirror is P 1 20cm 3 15cm 15cm 10cm 2 10cm 4 30cm

WISH O A glass hemisphere of refractive index 4 3 and of radius 4 cm is placed on a plane mirror A point object is placed at distance d on axis of this sphere as shown If the final image is at infinity then find the value of d in cm 3 94 34 cm by feel te ne va fagdag cm yang and forg OPTIONS MARK FOR REVIEW CLEAR SELECTION A 3