Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Diamond dazzles in dark.
Reason (R): It has low refractive index.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) is correct but (R) is not correct
A diamond sparkles because of total internal reflection: light that enters it is reflected again and again inside before it comes out. This happens because diamond has a very high refractive index (about 2.42), which gives it a very small critical angle (about 24°).
Assertion (A): Diamond dazzles in dark. True. Even in dim light a diamond catches the little light that falls on it, reflects it many times inside and sends it out through a few faces, so it shines brightly.
Reason (R): It has low refractive index. False. Diamond has one of the highest refractive indices of all transparent substances; a low refractive index would give a large critical angle and little sparkle.