Ray Optics and Optical Instruments

A thin biconvex lens is prepared from the glass ( =1.5) both curved surfaces of which have equal radii of 20 cm each. Left side surface of the lens is silvered from outside to make it reflecting. To have the position of image and object at the same place, the object should be placed, from the lens at a distance of cm.

1. 10
2. 12.5
3. 13
4. 13.5

Light ray incident along a vector AO ( AO=2 i-3 j ) emerges out along vector OB ( OB=C i-4 j ) as shown in the figure below. The value of C is . [figure]

1. 1.6
2. 0.16
3. 11.6
4. 16

A spherical interface lens of radius R separates two media of refractive indices 1 and 1.4 respectively as shown in the figure below. A point source is placed at a distance of 4R in front of spherical interface. The magnitude of the magnification of point source image is . [figure]

1. 1.66
2. 2.33
3. 2.66
4. 1.33

Angle of minimum deviation is equal to the half of the angle of prism in an equilateral prism. The refractive index of the prism is .

1. 1.5
2. 3
3. 2
4. 1.65

A ray of light passing through an equilateral prism is having velocity 2.12 108 m/s in the prism material, then the minimum angle of deviation is degrees.

1. 45
2. 30
3. 28
4. 58

A compound microscope is designed with two symmetric biconvex lenses. The objective lens is cut vertically, creating two identical plano-convex lenses. One of them is used in place of original objective lens. To retain same magnification keeping the object distance unchanged, the tube length has to be

1. increased two times
2. increased 32 times
3. decreased two times
4. decreased 32 times

A thin convex lens and a thin concave lens are kept in contact and are co-axial. Which of the following statements is correct for this combination of two lenses ?

1. behaves as concave lens if |fconvex|>|fconcave|
2. behaves as concave lens if |fconvex|<|fconcave|
3. behaves as convex lens if |fconvex|>|fconcave|
4. Focal length of the lens system will change if the positions of two lenses are interchanged

An object AB is placed 15 cm on the left of a convex lens P of focal length 10 cm. Another convex lens Q is now placed 15 cm right of lens P. If the focal length of lens Q is 15 cm, the final image is .

1. virtual, formed at 7.5 cm right of lens Q, with a size bigger than that of AB
2. real, formed at 7.5 cm right of lens Q, with a size same as that of AB
3. formed at infinity.
4. real, formed at 7 cm right of lens Q, with a size smaller than that of AB

A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm as shown in figure. The length of the image is cm. [figure]

1. 2.5
2. 5
3. 7.5
4. 7

A convex lens is made from glass material having refractive index of 1.4 with same radius of curvature on both sides. The ratio of its focal length and radius of curvature is .

1. 0.5
2. 2.5
3. 0.8
4. 1.25

For a thin symmetric prism made of glass (refractive index 1.5), the ratio of incident angle and minimum deviation will be .

1. 3 : 4
2. 3 : 2
3. 2 : 1
4. 1 : 2

Refer the figure given below. 1 and 2 are refractive indices of air and lens material. The height of image will be cm. [figure]

1. 1
2. 0.5
3. 1.2
4. 0.25

One side of an equilateral prism is painted by a transparent material of refractive index n2. The refractive index of prism is 1.6. The minimum value of n2 required for total internal reflection from painted face is . [figure]

1. 3 31.6
2. 3
3. 3.2 3
4. 4 35

The magnitudes of power of a biconvex lens (refractive index 1.5) and that of a plano-concave lens (refractive index = 1.7) are same. If the curvature of plano-concave lens exactly matches with the curvature of back surface of the biconvex lens, then ratio of radius of curvature of front and back surface of the biconvex lens is

1. 2 : 5
2. 5 : 2
3. 12 : 5
4. 5 : 12

A biconvex lens is formed by using two thin planoconvex lenses, as shown in the figure. The refractive index and radius of curved surfaces are also mentioned in figure. When an object is placed on the left side of lens at a distance of 30 cm from the biconvex lens, the magnification of the image will be : [figure]

1. −2
2. −2.5
3. +2.5
4. +2

For a transparent prism, if the angle of minimum deviation is equal to its refracting angle, the refractive index n of the prism satisfies.

1. n 2
2. 2 < n < 2
3. 1 < n < 2
4. 2 < n < 2 2

The exit surface of a prism with refractive index n is coated with a material having refractive index n2. When this prism is set for minimum angle of deviation, it exactly meets the condition of critical angle. The prism angle is .

1. 60
2. 30
3. 15
4. 45

In a microscope of tube length 10 cm two convex lenses are arranged with focal lengths of 2 cm and 5 cm. Total magnification obtained with this system for normal adjustment is (5)k. The value of k is .

1. 4
2. 5
3. 2
4. 3.5

Distance between an object and three times magnified real image is 40 cm. The focal length of the mirror used is cm.

1. -20
2. -15/2
3. -10
4. -15

Five persons P1, P2, P3, P4 and P5 recorded object distance (u) and image distance (v) using same convex lens having power +5 D as (25, 96), (30, 62), (35, 37), (45, 35) and (50, 32) respectively. Identify correct statement

1. Readings recorded by P3 and P2 persons are incorrect
2. Readings recorded by all persons are correct
3. Readings recorded by P3 person are incorrect
4. Readings recorded by P4 and P5 persons are incorrect

A thin prism with angle 5 of refractive index 1.72 is combined with another prism of refractive index 1.9 to produce dispersion without deviation. The angle of second prism is .

1. 5
2. 4
3. 4.5
4. 6

Consider light travelling from a medium A to medium B separated by a plane interface. If the light undergoes total internal reflection during its travel from medium A to B and the speed of light in media A and B are 2.4 108 m/s and 2.7 108 m/s, respectively, then the value of critical angle is :

1. -1 ( 89 )
2. -1 ( 98 )
3. -1 ( 3 13 )
4. -1 ( 8 17 )

A thin convex lens of focal length 5 cm and a thin concave lens of focal length 4 cm are combined together (without any gap) and this combination has magnification m1 when an object is placed 10 cm before the convex lens. Keeping the positions of convex lens and object undisturbed a gap of 1 cm is introduced between the lenses by moving the concave lens away, which leads to a change in magnification of total lens system to m2. The value of | m1m2 | is .

1. 2527
2. 56
3. 527
4. 32

Consider an equilateral prism (refractive index 2). A ray of light is incident on its one surface at a certain angle i. If the emergent ray is found to graze along the other surface then the angle of refraction at the incident surface is close to

1. 30
2. 20
3. 40
4. 15

The wavelength of light, while it is passing through water is 540 nm. The refractive index of water is 4/3. The wavelength of the same light when it is passing through a transparent medium having refractive index of 3/2 is nm.

1. 540
2. 840
3. 480
4. 380

As shown in the diagram, when the incident ray is parallel to base of the prism, the emergent ray grazes along the second surface. [figure] If refractive index of the material of prism is 2, the angle of prism is.

1. 75
2. 90
3. 60
4. 45

A convex lens of focal length 30 cm is placed in contact with a concave lens of focal length 20 cm. An object is placed at 20 cm to the left of this lens system. The distance of the image from the lens in cm is .

1. 607
2. 15
3. 45
4. 30

A concave-convex lens of refractive index 1.5 and the radii of curvature of its surfaces are 30 cm and 20 cm, respectively. The concave surface is upwards and is filled with a liquid of refractive index 1.3. The focal length of the liquid-glass combination will be

1. 70011 cm
2. 60011 cm
3. 80011 cm
4. 50011 cm

Two thin convex lenses of focal lengths 30 cm and 10 cm are placed coaxially, 10 cm apart. The power of this combination is:

1. 5 D
2. 1 D
3. 20 D
4. 10 D

A lens having refractive index 1.6 has focal length of 12 cm, when it is in air. Find the focal length of the lens when it is placed in water. (Take refractive index of water as 1.28)

1. 355 mm
2. 655 mm
3. 288 mm
4. 555 mm