A point object is placed at a distance of 60 cm from a convex lens of focal length 30 cm. If a plane mirror were put perpendicular to the principal axis of the lens and at a distance of 40 cm from it, the final image would be formed at a distance of:
1. 30 cm from the plane mirror, it would be a
2. 20 cm from the plane mirror, it would be a
3. 20 cm from the lens, it would be a real image.
4. 30 cm from the lens, it would be a real image.
A lens of large focal length and large aperture is best suited as an objective of an astronomical telescope since:
1. a large aperture contributes to the quality
and visibility of the images.
2. a large area of the objective ensures better
3. a large aperture provides
a better resolution.
4. all of the above.
A convex lens 'A' of focal length 20 cm and a concave lens 'B' of focal length 5 cm are kept along the same axis with a distance 'd' between them. If a parallel beam of light falling on 'A' leaves 'B' as a parallel beam, then the distance 'd ' in cm will be:
Find the value of the angle of emergence from the prism given below for the incidence ray shown. The refractive index of the glass is .
A biconvex lens is cut into two halves along (i) XOX' and (ii) YOY' as shown in the figure. Let f, f' f" be the focal lengths of the complete lens, of each half in case (i), and of each half in case (ii), respectively.
Choose the correct statement from the following:
1. f' = f, f" = 2f
2. f' = 2f, f" = f
3. f' = f, f" = f
4. f' = 2f, f" = 2f
A convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens. Then its focal length will:
1. become zero.
2. become infinite.
3. become small, but non-zero.
4. remain unchanged.
Optical fibre is based on:
1. total internal reflection
2. less scattering
4. less absorption coefficient
A ray of light travelling in the air has wavelength λ, frequency n, velocity v and intensity I. If this ray enters into water then these parameters are λ', n', v' and I' respectively. Which relation is correct?
1. λ = λ′
2. n = n′
3. v = v′
4. I = I′
A disc is placed on the surface of a pond which has a refractive index of . A source of light is placed 4 m below the surface of liquid. Find The minimum radius of a disc so that light does not come out from it.
2. 3 m
3. 6 m
4. 4 m
In a compound microscope, the magnification is 95, the distance of the object from the objective lens is 1/3.8 cm and the focal length of the objective is 1/4 cm. What is the magnification of the eyepiece when the final image is formed at the least distance of distinct vision?