10 Question-answer on refraction of light
1. The focal length of an equiconvex lens in air is equal to either of its radii of curvature. The refractive index of the material of the lens is:
(a) 4/3
(b) 2.5
(c) 0.8
(d) 1.5
Ans: (d)
2. Two lenses of power 2.5 D and 1.5 D are joined together. The power of the new lens formed is:
(a) 1.0 D
(b) 5/3 D
(c) 3/5 D
(d) 4.0 D
Ans: (d)
3. A tank is height 40 m is filled with oil fully. If the bottom of the tank appears to be 30 m below its top, the refractive index of the oil should be
(a) ¾
(b) 3/2
(c) 3/8
(d) 4/3
Ans: (d)
4. If critical angle for a material to air is 30˚, then refractive index of the material will be:
(a) 1.0
(b) 1.5
(c) 2.0
(d) 2.5
Ans: (c)
5. A fish 10 cm long is 4 cm under the water level. Its length when viewed vertically above will be:
(a) 10 cm
(b) 3 cm
(c) 7.5 cm
(d) 8 cm
Ans: ( a)
6. One cannot see through fog because
(a) Fog absorbs light
(b) The refractive index of fog is infinity
(c) Light suffers total reflection at the droplet in fog
(d) Light is scattered by the droplets in fog.
Ans: (d)
7. It is possible to observe total internal reflection when a ray travels from
(a) Air into water
(b) Air into glass
(c) Water into glass
(d) Glass into water
Ans: (d)
8. A completely transparent material will be invisible in vacuum when its refractive index ยต is:
(a) Unity
(b) More than unity
(c) Less than unity
(d) Equal to 1.33
Ans: (a)
9. A well cut diamond appears bright because
(a) It emits light
(b) It is radioactive
(c) Of total internal reflection
(d) It has high density.
Ans: (c)
10. Mirages are observed in deserts due to the phenomenon of
(a) Interference of light
(b) Total internal reflection of light
(c) Scattering of light
(d) Double refraction of light
Ans: (b)