Important questions based on NCERT syllabus for Chapter 10 - Light Reflection and Refraction:
Question-1: A ray of light travelling in air enters obliquely into water. Does the light ray bend towards the normal or away from the normal? Why?
Solution: 1. The ray of light bends towards the normal.
2. When a ray of light enters from an optically rarer medium (having a low refractive index) to an optically denser medium (having a high refractive index), its speed slows down and it bends towards the normal.
3. Since water is optically denser than air, a ray of light entering from air into water will bend towards the normal.
Question-2: The refractive index of diamond in much greater than that of ordinary glass. Is this fact of some use to a diamond-cutter?
Solution: 1. Refractive index of diamond is nearly 2.42. It is much larger than that of ordinary glass (nearly 1.5).
2. The critical angle for diamond is nearly 240. This is much less than that of glass.
3. A skilled diamond cutter exploits the large range of angle of incidence (in the diamond) 240 to 900, to ensure that light entering the diamond is totally reflected from many faces before getting out. This produces brilliance i.e., sparkling effect in the diamond.
Question-3: A concave mirror is held in water. What would be the change in the focal length of the mirror?
Solution: Zero. Focal point of the mirror only depends on the centre of curvature and not on the medium it is placed in.