Ray Optics and Optical Instruments · Question 37

Two identical thin plano-convex glass lenses (refractive index 1.5) each having radius of curvature of 20 cm are placed with their convex surfaces in contact at the centre. The intervening space is filled with oil of refractive index 1.7. The focal length of the combination is

1. -50 cm
2. 50 cm
3. -20 cm
4. -25 cm

The refracting angle of a prism is A, and refractive index of the material of the prism is (A/2). The angle of minimum deviation is

1. 90 - A
2. 180 + 2A
3. 180 - 3A
4. 180 - 2A

If the focal length of objective lens is increased then magnifying power of

1. microscope will increase but that of telescope decrease.
2. microscope and telescope both will increase.
3. microscope and telescope both will decrease.
4. microscope will decrease but that of telescope will increase.

The angle of a prism is A. One of its refracting surfaces is silvered. Light rays falling at an angle of incidence 2A on the first surface return back through the same path after suffering reflection at the silvered surface. The refractive index , of the prism is

1. 2sinA
2. 2cosA
3. 12cosA
4. tanA

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