Ray Optics and Optical Instruments · Question 52

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

Two thin lenses of focal lengths f1 and f2 are in contact and coaxial. The power of the combination is

1. f1 + f22
2. f1 + f2f1 f2
3. f1f2
4. f2f1

A boy is trying to start a fire by focusing sunlight on a piece of paper using an equiconvex lens of focal length 10 cm. The diameter of the sun is 1.39 109 m and its mean distance from the earth is 1.5 1011 m. What is the diameter of the sun's image on the paper ?

1. 6.5 10-5 m
2. 12.4 10-4 m
3. 9.2 10-4 m
4. 6.5 10-4 m

A small coin is resting on the bottom of a beaker filled with liquid. A ray of light from the coin travels up to the surface of the liquid and moves along its surface. How fast is the light travelling in the liquid? [figure]

1. 2.4 108 m/s
2. 3.0 108 m/s
3. 1.2 108 m/s
4. 1.8 108 m/s