Ray Optics and Optical Instruments · Question 41

A plano convex lens fits exactly into a plano concave lens. Their plane surfaces are parallel to each other. If lenses are made of different materials of refractive indices 1 and 2 and R is the radius of curvature of the curved surface of the lenses, then the focal length of the combination is

1. R( 1- 2)
2. 2R( 2- 1)
3. R2( 1+ 2)
4. R2( 1- 2)

For a normal eye, the cornea of eye provides a converging power of 40 D and the least converging power of the eye lens behind the cornea is 20 D. Using this information, the distance between the retina and the cornea-eye lens can be estimated to be

1. 1.67 cm
2. 1.5 cm
3. 5 cm
4. 2.5 cm

The reddish appearance of the sun at sunrise and sunset is due to

1. the scattering of light
2. the polarisation of light
3. the colour of the sun
4. the colour of the sky

Two plane mirrors are inclined at 70 . A ray incident on one mirror at angle , after reflection falls on second mirror and is reflected from there parallel to first mirror. The value of is

1. 45
2. 30
3. 55
4. 50

For the angle of minimum deviation of a prism to be equal to its refracting angle, the prism must be made of a material whose refractive index

1. lies between 2 and 1
2. lies between 2 and 2
3. is less than 1
4. is greater than 2

A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that its end closer to the pole is 20 cm away from the mirror. The length of the image is

1. 10 cm
2. 15 cm
3. 2.5 cm
4. 5 cm

When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid, it acts as a plane sheet of glass. This implies that the liquid must have refractive index

1. equal to that of glass
2. less than one
3. greater than that of glass
4. less than that of glass

A ray of light is incident at an angle of incidence i, on one face of a prism of angle A (assumed to be small) and emerges normally from the opposite face. If the refractive index of the prism is , the angle of incidence i, is nearly equal to

1. A
2. A2
3. A
4. A2

A concave mirror of focal length f1 is placed at a distance of d from a convex lens of focal length f2. A beam of light coming from infinity and falling on this convex lens – concave mirror combination returns to infinity. The distance d must equal

1. f1 + f2
2. -f1 + f2
3. 2f1 + f2
4. -2f1 + f2

The magnifying power of a telescope is 9. When it is adjusted for parallel rays the distance between the objective and eyepiece is 20 cm. The focal length of lenses are

1. 10 cm, 10 cm
2. 15 cm, 5 cm
3. 18 cm, 2 cm
4. 11 cm, 9 cm