Previous Year Question
A cut diamond shines brilliantly due to
some inherent property
total internal reflection
its molecular structure
absorption of light
Correct Answer: B
Detailed Solution
Diamond has a very high refractive index of about 2.42. Consequently, its critical angle at the diamond-air interface is only about 24.4°.
When light enters a properly cut diamond, its facets are arranged in such a way that many light rays strike the internal surfaces at angles greater than the critical angle.
Under these conditions, instead of being refracted out, the rays undergo repeated Total Internal Reflection inside the diamond. After several internal reflections, a substantial amount of light emerges towards the observer, producing the characteristic brilliance of a cut diamond.
The basic conditions for Total Internal Reflection are that light must travel from an optically denser medium towards a rarer medium and the angle of incidence must be greater than the critical angle.
Diamond also produces dispersion, which contributes to coloured flashes.