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 concave mirror of focal length 10 cm forms an image which is double the size of object when the object is placed at two different positions. The distance between the two positions of the object is cm.

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

If sunlight is focused on a paper using convex lens, it starts burning the paper in shortest time when the lens is kept at 30 cm above the paper. If the radius of curvature of the lens is 60 cm then the refractive index of the lens material is 10. The value of is .

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 convex lens of refractive index 1.5 and focal length f = 18 cm is immersed in water. The difference in focal lengths of the given lens when it is in water and in air is f. The value of is . (refractive index of water = 4/3)

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 prism of angle 75 and refractive index 3 is coated with thin film of refractive index 1.5 only at the back exit surface. To have total internal reflection at the back exit surface the incident angle must be ( 15 = 0.25 and 25 = 0.43)

1. between 15 and 20
2. 15
3. < 15
4. > 25

The size of the images of an object, formed by a thin lens are equal when the object is placed at two different positions 8 cm and 24 cm from the lens. The focal length of the lens is cm.

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

A parallel beam of light travelling in air (refractive index 1.0) is incident on a convex spherical glass surface of radius of curvature 50 cm. Refractive index of glass is 1.5. The rays converge to a point at a distance x cm from the centre of curvature of the spherical surface. The value of x is cm.