# Her friend noted the following observations from this demonstration :

Q.) Her friend noted the following observations
from this demonstration :

(I) Glass is optically rarer than air.

(II) Air and glass allow light to pass through them with the same velocity.

(III)Air is optically rarer than glass.

(IV)Speed of light through a denser medium is faster than that of a rarer medium.

(V) The ratio: sin of angle of incidence in the first medium to the ratio of sin of angle of refraction in the second medium, gives the refractive index of the second material with respect to the first one.

Which one of the combination of the above statements given below is correct.

(a) (II), (IV) and (V) are correct.

(b) (III) and (IV) are correct.

(c) (I), (IV) and (V) are correct.

(d) (III) and (V) are correct.

Ans. (d) (III) and (V) are correct.

Explanation: As light bends towards the normal when it travels from air to glass, air is rare than glass, which means that the refractive index of air is less than that of glass. The refractive index of a medium 2 with respect to medium 1 or n21 is the ratio of sine of angle of incidence i to the sine of angle of refraction r which can be written as sin sin r i = n21.