a) Explain what is meant by(i) total internal reflection, [1] (ii) critical angle. [1] (b) (i) The speed of light in air is 3.0 × 10^8 m / s. Its speed in glass is 2.0 × 10^8 m / s. Calculate the refractive index of the glass. [2] (ii) Show that the critical angle for the glass-air boundary is 42° [2]
Answers
Answer:
a) (i)Total internal reflection, in physics, complete reflection of a ray of light within a medium such as water or glass from the surrounding surfaces back into the medium.
(ii)The phenomenon occurs if the angle of incidence is greater than a certain limiting angle, called the critical angle.
(b) (i)Glass refractive index is defined as the ratio between the speed of light in the vacuum and the speed of light in the glass.
Refractive index of glass (ng) = Speed of light in vacuum/speed of light in the glass.
ng = (3 ×108)/ (2 ×108)
ng = 1.5
(ii)At a certain angle of incidence, the light will refract 90 degrees and travel along the boundary between the two media. This angle of incidence is called the critical angle. The critical angle varies for different materials, but it is useful to know that it is around 42 degrees for glass.