CLASS X
TOPIC- LIGHT REFRACTION
1. (a) Refractive index of water is 4/3 and glass is 3/2 with regard to air. What is the
refractive index of glass with respect to water?
(b) Refractive index of diamond w.rt glass is 1.6 and refractive index of glass is 1.5.
Find the absolute refractive index of diamond.
2. How are the power and the focal length related? There are two lenses of focal length
20cm and 40cm respectively. Which lens will you use to obtain more convergent light
and why? Also find the combined focal length of the combination of the above
lenses.
3. An object is placed at a distance of 50 cm froma concave lens of focal length 30
cm. Find the position and nature of the image formed.
4. The image obtained with a convex lens is erect and its length is 4 times the length
of the object. If the focal length is 20 cm, calculate the object and image distances.
5. Calculate two distances at which an object should be placed in front of a convex
lens of focal length 10 cmto obtain an image of double its size.
6. Aray of light enters in flint glass from air. The refractive index of flint glass air with
respect air is 1.65, by what %does the speed of light reduces on entering flint glass?
7. Aray of light of wavelength 600 nm enters from air to kerosene. Calculate () speed
of light in kerosene (i) wavelength of light in kerosene and (ii) frequency of the wave,
If the refractive index of kerosene is 1.4.
8. Calculate the refractive index of a medium if the wavelength of light entering from
air to this medium decreases by 10%. Also calculate () speed of light in the medium
and (ii) frequency of the wave.
9 (a) An object is placed at a distance of 15cm froma convex mirror of focal length
30cm. Find the position and the nature of the image.
(b) Aconcave lens has focal length of 15cm, at what distance should the object from
the lens be placed so that it forms an image at 10cm from the lens? Also find the
magnification produced by the lens.
10. A concave lens made up of material of refractive index n, is kept in a medium of
refractive index n2.
Aparallel beam of light is incident on the lens. Complete the path of rays of light
emerging fromthe concave lens if (i) ni>nz (ii) ni =nz (ii) n < n2.
11. Aconcave lens is kept in contact with a convex lens of focal length 20 cm. The
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combination works as a converging lens of focal length 100 cm. Calculate power of
concave lens.
