Question Pool Ray Optics and Optical Instruments

Ray Optics and Optical Instruments - SAMAGRA Question Pool & Answers | Class 12

Kerala Syllabus SAMAGRA SCERT SAMAGRA Question Pool for Class 12 Physics Ray Optics and Optical Instruments

Qn 1.

A compound microscope consists of an objective lens of focal length 2 cm and an eyepiece of focal length 6.25 cm separated by a distance of 15 cm. How far from the objective should an object be placed in order to obtain the final image at

(a) least distance of distinct vision

(b) infinity

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Qn 2.

The given figure shows a compound microscope with two lenses PQ and RS

(a) Identify Objective and eyepiece in the microscope

(b) A compound microscope has a magnification of 30. The focal length of its eyepiece is 5 cm. Assuming the final image to be formed at the least distance of distinct vision, calculate the magnification produced by the objective.

(c) What is the length of a compound microscope in normal adjustment.

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Qn 3.

The given figure shows a simple microscope

(a) Identify the object distance and image distance

(b)Derive an equation for magnifying power of the simple microscope.

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Qn 4.
1. Blue colour of the sky is due to………………

2. A transparent container containing water is illuminated by narrow beams of red and green lights . Which colour will be more intense in the solution. Why?

1. Scattering

2. Green. Green light is more scattered than red light

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Qn 5.

A light ray us incident on the face AB of an equilateral prism as shown.

1. A light ray incident on one face of the above equilateral prism ABC having refractive index 1.5 emerges by grazing through the face AC. Find the angle of incidence on the face AC.

2. Draw the path of the ray when it is coming out through the face AC.

3. Write down the expression for the refractive index of the material of the prism in terms of angle of minimum deviation.

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Qn 6.

The figure shows the propagation of light through an optical fibre.

1. Name the principle guiding the propagation of light through an optical fibre.

2. Write the necessary conditions for the above phenomenon.

3. Diamond has refractive index 2.42.Calculate the critical angle for diamond. If the diamond crystal is placed in a liquid of refractive index 1.3 what will be the critical angle?

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Qn 7.

Certain prisms are designed to bend light by 900 and by 1800.

(a) These prisms make use of the phenomenon called ………….. ………………

(b) Two rays of light — red and blue — are incident on the face AB of a right angled prism ABC. The refractive indices of the material of the prism for red and blue wavelengths are 1.39 and 1.47 respectively. Trace the path of the rays through the prism

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Qn 8.

You are given two mirrors labeled A and B. When you look at them keeping it close to your face a magnified image is seen in mirror A and a diminished image is seen in the mirror B.

1.Identify the mirrors A and B

2. Draw the ray diagram in which the mirror forms magnified erect image.

3. Let the focal length of the mirror you used in the above question is 20 cm. At what distance an object must be placed in front of the mirror so that an image magnified three times is formed on a screen?

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Qn 9.

A ray of light parallel to the principal axis of a spherical mirror falls at a point M as shown in

1. Identify the type of the mirror used in the diagram.

2. If focal length of the mirror is 10 cm, what is the distance CF in the figure?

3. Complete the ray diagram and mark the angle of incidence and angle of reflection

4. If the mirror is immersed in water its focal length will be                                                                                            (i) less than 10 cm (ii) 10 cm (iii) greater than 10 cm (iv) 20 cm

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Qn 10.

Fill in the blanks in three coloumns

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Qn 11.

A concave mirror is held in water. What should be the change in the focal length of the mirror?

No change. The focal length of a concave mirror does not depend on the nature of the

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Qn 12.

Two concave mirrors have the same focal length but the aperture of one is larger than that of the other. Which mirror forms the sharper image and why?

The concave mirror with smaller aperture forms the sharper image because it is free from spherical

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Qn 13.
1. An astronomical telescope has a large aperture to

(a)reduce spherical aberration

(b)have high resolution

(c) increases span of observation

(d)have low dispersion

(b)have high

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Qn 14.

To increase the angular magnification of a simple microscope, one should increase

(a)the focal length of the lens

(b)the power of the lens

(c)the aperture of the lens

(d)the object size

(b)the power of the

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Qn 15.

The image formed by an objective of a compound microscope is

(a) real and diminished                                  (b) real and enlarged

(c) virtual and enlarged                                  (d) virtual and diminished

(b) real and

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Qn 16.

Astigmatism is corrected using

(a) cylindrical lens                                         (b) plano-convex lens

(c) plano-concave lens                                  (d) convex lens

.(a) cylindrical

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Qn 17.

Identify the mismatch in the following

(a)Myopia - Concave lens

(b)For rear view - Concave mirror

(c)Hypermetropia - Convex lens

(d)Astigmatism - Cylindrical lens

(b)For rear view - Concave

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Qn 18.

In secondary rainbow what is the order of colours observed from earth?

(a)Violet innermost, red outermost.

(b)Red innermost, violet outer most.

(c)Random.

(d)White and dark alternatively.

(b)Red innermost, violet outer

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Qn 19.

When light rays undergoes two internal reflection inside a raindrop, which of the rainbow is formed?

(a) Primary rainbow                          (b) Secondary rainbow

(c) Both (a) and (b)                           (d) Can’t say

(b) Secondary

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Qn 20.

(i) draw a ray diagram showing the image formation by a compound microscope. Obtain expression for total magnification when the image is formed at infinity.

ii) how does the resolving power of a compound microscope get affected , when

a) diameter of objective is increased and focal length is increased.

b) the wavelength of light is increased?

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Qn 21.

Draw a ray diagram to show image formation when the concave mirror produces a real inverted and magnified image of the object

ii) obtain the mirror formula and write the expression for the linear magnification.

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Qn 22.

You are given three lenses having powers P and aperture A as follows

P1 = 6D. A1 = 3cm

P2 = 3D. A2 = 15cm

P3 = 6D.A3 = 1.5 cm

Which two of these will you select to construct (i) a telescope and (ii) a microscope?

state the basis for your answer in each case.

For telescope :

1. Objective- more focal length ,less power ,more

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Qn 23.

By drawing the ray diagram

a) show that how a right angled isosceles prism can be used to deviate A Ray of light through (i) 90° ( ii)180°? b) calculate the value of refractive index if critical angle is 45 °.

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Qn 24.

A concave lens made of a material of refractive index n2 is kept in a medium of refractive index n1. A parallel beam of light is incident on the lens. Complete the path of rays of light emerging from the concave lens

If (i) n1 > n2

(ii) n1 = n2

(iii) n1 < n2

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Qn 25.

Power of a concave lens is

a) zero        b) infinite         c) positive        d) negative.

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Qn 26.

Power of a convex lense is

a) zero     b) infinite      c) positive       d) negative

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Qn 27.

i) define the magnifying power of a compound microscope when the final image is formed at infinity.

ii) does the magnifying power of a microscope depend on the colour of the light used? Justify your answer.

iii) both the objective and eyepiece of a compound microscope have short focal lengths. Why?

magnifying power is defined as the angle subtended by the image to the angle subtended (at the unaided eye) by the

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Qn 28.

A convex lens is used as a simple microscope.

i) draw the ray diagram of the simple microscope and locate the position of objects.

ii) what is the nature of the image?

iii) A magnifying glass is made of a combination of a convex lens of power 21 D and a concave lens of -5D. If the distance of distinct vision of the eye is 25 cm, calculate the magnifying power?

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Qn 29.

"Sunglasses aur goggles has zero power even though its surface is covered".

i) do you agree with the statement? Justify your answer.

yes. since the two surfaces are curved in the same direction and also the curvatures

R1 =

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Qn 30.

A number of concentric coloured arc are seen in the sky after the rain when the sun is behind the observer, is called rainbow

i) the second rainbow has inverted colours why

ii) can any two people see the same rainbow .Give reason for your answer.

i) light enters from the bottom of the drop . Two refraction and two internal reflection takes place and hence secondary rainbow

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Qn 31.

when a ray of light incident on a convex lens , after refraction, they converge to a point On the principal axis.

i) what do you observe in the figure?

ii) what is the name given to this defect? explain.

iii) How cab it be rectified?

i) in the figure violet rays are focused near to the lens and rays are focused further from the lens.

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Qn 32.

A white light is passed through a prism .

i) what happens as the ray emerges out from the prism .

ii) what is the phenomenon called and which colour deviates maximum and least?

iii) what is dispersive power? Give an expression for dispersive power.

i) white light split up into its constituent colours.

ii)

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Qn 33.

i) Draw a ray diagram to show the image formation by a combination of two thin convex lenses in contact .Obtain the expression for the power of this combination in terms of the focal lengths of the lenses.

ii) what is the advantage in the combination?

iii) if one of the lenses is concave how will you find its focal length with the help of lens combination?

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Qn 34.

An object is placed in front of convex lens made of glass.How does the image distance vary if the refractive index of the medium is increased in such a way that still it remains less than the glass?

from the lens makers formula

1/f =( n21 - 1)(1/R1 -

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Qn 35.

i) A fish underwater looks obliquely at a fisherman standing on the bank of a lake. Would the fisherman look taller or shorter to the fishr than what he actually is?

ii) a small pin fixed on a table top is viewed from above from a distance of 40 cm .By what distance would the pin appear to be raised if it is viewed from the same point through a 15 cm thick glass slab held parallel to the table? refractive index of glass is 1.49 . Does the answer depend on the location of the slab?

i) taller

ii) t = d [1 - 1/n

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Qn 36.

What is the focal length of a convex lens of focal length 25 cm in contact with a concave lens of focal length 15 cm? Is the system a converging or a diverging lens? Ignore thickness of the lenses.

f1 = 25 cm, f= -15 cm

f =

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Qn 37.

(i) Draw the ray diagram showing refraction of light through a glass prism and hence obtain the relation between the refractive index of the prism , angle of prism and angle of minimum deviation.

ii) determine the value of angle of incidents for a ray of light travelling from a medium of refractive index n = √2 into the medium of n = 1 , so that it just graces along the surface of separation.

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Qn 38.

(i) plot a graph to show variation of the angle of deviation as a function of angle of incidence for light passing through a prism.

derive an expression for refractive index of the prism in terms of angle of minimum deviation and angle of prism. (3)

ii) A Ray of light incident on an equi lateral glass prism of refractive index 1.73 moves parallel to the base line of the prism inside it. Find the angle of incidence for this ray. (2)

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Qn 39.

How does the angle of minimum deviation of a glass prism vary if the incident violet light is replaced by red light? give reason.

decreases ,

Refractive index of violet is greater than refractive index of

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Qn 40.

A pulse of white light is incident from air to a glass slab at normal incidence. After travelling through the slab the first colour to emerge is

a) blue       b) green        c) violet        d) red

red

We know that

V = ν

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Qn 41.

splitting up of white light into its constituent colours while passing through a transparent medium is called dispersion.

(i) why does this happens ?

(ii) show by drawing diagrams how one understands formation of a rainbow.

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Qn 42.

i) write the necessary conditions for the phenomenon of total internal reflection to occur.

(ii) write the relation between critical angle and refractive index for a given pair of optical media.  Does critical angle

depend on the colour of light?. explain.

i) (a) the ray should travel from denser medium to rarer medium.

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Qn 43.

i) Calculate the distance of an object of of height h from a concave mirror of radius of curvature 20 cm, so as to obtain a real image of magnification 2. Find the location of the image also.

ii) using mirror formula explain why does a convex mirror always produce a virtual image.

i) given R = 20 cm magnification m = - 2.

f = R/2 = -10 cm.

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Qn 44.

State two positions in which a concave mirror produces a magnified image of a given object.

1 . object is between centre of curvature and principal focus of the mirror.

2. Object is

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Qn 45.

A concave or convex mirror is held under water will its focal length change ?

No ,the focal length of small aperture mirror is half of its radius it does not depends upon the refractive index of the surrounding

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Qn 46.

An object AB is kept in front of a concave mirror as shown in the figure.

i) complete the ray diagram showing the image formation of the object.

ii) how will the position and intensity of the image be affected if the lower half of the mirror reflecting surface is painted black?

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Qn 47.

. Name the mirror which are used in

(i) security mirror

(ii) solar furnace.

(I) convex mirror

(ii) concave

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Qn 48.

Name the mirror which are used in

(i) security mirror

(ii) solar furnace.

(I) convex mirror

(ii) concave

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Qn 49.

When an object is placed 20 cm in front of a spherical mirror it produces an erect image of magnification 1/ 5.

a) what is the focal length of the sperical mirror?

b) what kind of mirror is it?

a) m = 1/5

u = -29cm,  f = ?

m = f

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Qn 50.

A boy uses spectacles of power - 0.75 D.

a) name the defect of vision he is suffering from.

b) which type of lens is used and why?

a) short sight.

b) concave lens is used.

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Qn 51.

During sunrise and sunset sun appears in crimson red. Name and explain the phenomenon.

Scattering.

At the time of sunrise or sunset sun rays have to travel longer distances during his travel shorter wavelength gets scattered as you

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Qn 52.

"Sun becomes visible before actual sunrise" Do you agree with the statement?. Explain.

yes, I agree with the above statement

it is due to atmospheric refraction of light. When

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Qn 53.

Match the following

A                                                                                    B

1. Resolving power of telescope                                                   Concave lens

2. Telescope                                                                                  D/1.22λ

3. Short sight                                                                                 m  = fo/fe [1+fe/D]

4. Reading lens                                                                              m = L/fo [1+D/fe]

Convex lens.

1.22λ/D

1. m= fo/fe[1+fe/D]

2.

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Qn 54.

i) You are given three lenses of power. 5D,4D and 10D to design a telescope.

a) which lenses should be used as objective and eyepiece. Justify your answer.

b) Why is the aperture of the objective preferred to be large?

ii) Write any two advantages of a reflecting telescope over a refracting telescope

i) a) objective = 5 D

Eye lens = 10D.

m =

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Qn 55.

"A Ray of light shows no dispersion on emerging from a glass slab .But when it is passed through a Prism it shows dispersion" Do you agree with the above statement?. Justify your answer.

yes . In the case of glass slab the rays suffers no deviation but laterally displaced .