Question

(i) 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?

(ii)You are given kerosene, turpentine and water. In which of these does the light travel fastest?

Answer 1

(i) The ray of light bends towards the normal. When a ray of light enters from an optically rarer medium (having low refractive index) to an optically denser medium (having high refractive index), its speed slows down and it bends towards the normal. Since, water is optically denser than air, a ray of light entering from air into water will bend towards the normal. 

(ii) Refractive index, 

n_water = 1.33 

n_kerosene = 1.44 

n_temperature = 1.47 

Speed of light in a medium of refractive index n is given by: 

ν = \(\frac{c}{n}\) ;c = speed of light in air 

= 3*10⁸ m/s 

Hence, for more ν, n should be less. 

Among the given media, refractive index of water is least. 

Hence, light travels fastest in water.

Answer 2

(i)  The ray of light will bend towards the normal because air is the rarer medium and water is denser medium . When ray of light enters a denser medium from a rarer medium its velocity get reduced and it bends towards the normal .

(ii) v = n₁/ n₂ , means lower the refractive index of second medium is greater the speed of light in that medium . 

Refractive index of water : 1.33

Refractive index of kerosene : 1.44

Refractive index of trumpentine : 1.47

Since the refactive index of water among all is the least the light will travel fastest in water .