Question

A cut diamond sparkles because of its:
A. High refractive index
B. Hardness
C. Emission of light by the diamond
D. Absorption of light by the diamond

Answer 1

Hint: The cut of a gemstone is an extremely important feature and is aimed to enhance the sparkle, glint or twinkle of the gem. Diamond is an allotrope of carbon. The other allotropes are the graphite and C-60 Buckminsterfullerene. The diamond is a nonmetal and is one of the hardest substances on the earth. It has a well defined shape.

Complete answer:
The "sparkle" is caused by the relative movement of your eyes with respect to the diamond. In certain positions your eyes are not in line with the refracted rays and the diamond looks dull. Then, because of the cut, even a slight relative movement (of the diamond, or your eyes, or both) causes your eyes to come in line with the refracted ray which you see suddenly as a burst of light. A cut diamond sparkles because of its high refractive index. Because of the high refractive index, the light suffers total internal reflections many times. That is why it sparkles.

So, the correct option is A.

Note: An essential characteristic of total internal reflection is that the reflected light wave remains in the same medium as the incident light (reflection occurs in the same medium and refraction occurs when the media are different. Total internal reflection occurs when the light travels from denser to rarer medium at an angle of incidence which is greater than the critical angle.