Ray Optics and Optical Instruments · Question 49

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

Which of the following is not due to total internal reflection ?

1. Working of optical fibre
2. Difference between apparent and real depth of a pond
3. Mirage on hot summer days
4. Brilliance of diamond

A biconvex lens has a radius of curvature of magnitude 20 cm. Which one of the following options best describes the image formed of an object of height 2 cm placed 30 cm from the lens ?

1. Virtual, upright, height = 1 cm
2. Virtual, upright, height = 0.5 cm
3. Real, inverted, height = 4 cm
4. Real, inverted, height = 1 cm

The speed of light in media M1 and M2 are 1.5 108 m/s and 2.0 108 m/s respectively. A ray of light enters from medium M1 to M2 at an incidence angle i. If the ray suffers total internal reflection, the value of i is

1. Equal to -1 ( 23 )
2. Equal to or less than -1 ( 35 )
3. Equal to or greater than -1 ( 34 )
4. Less than -1 ( 23 )

A ray of light is incident on a 60 prism at the minimum deviation position. The angle of refraction at the first face (i.e., incident face) of the prism is

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

A ray of light travelling in a transparent medium of refractive index , falls on a surface separating the medium from air at an angle of incidence of 45 . For which of the following value of the ray can undergo total internal reflection?

1. = 1.33
2. = 1.40
3. = 1.50
4. = 1.25

A lens having focal length f and aperture of diameter d forms an image of intensity I. Aperture of diameter d2 in central region of lens is covered by a black paper. Focal length of lens and intensity of image now will be respectively

1. f and I4
2. 3f4 and I2
3. f and 3I4
4. f2 and I2