Ray Optics and Optical Instruments · Question 43

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

A thin prism of angle 15 made of glass of refractive index 1 = 1.5 is combined with another prism of glass of refractive index 2 = 1.75. The combination of the prisms produces dispersion without deviation. The angle of the second prism should be

1. 5
2. 7
3. 10
4. 12

A converging beam of rays is incident on a diverging lens. Having passed through the lens the rays intersect at a point 15 cm from the lens on the opposite side. If the lens is removed the point where the rays meet will move 5 cm closer to the lens. The focal length of the lens is

1. 5 cm
2. -10 cm
3. 20 cm
4. -30 cm