KCL Section 4: Total internal reflection (Waves and photons)

Question 1

What is the critical angle?

Answer 1

The critical angle, C, is the value of θi when θr becomes 90 degrees.

n1 sin C = n2 sin 90
Since sin 90 = 1, this becomes:
n1 sin C = n2
sin C = n2/n1

Question 2

The refractive index is 1.50 for glass and 1.33 for water. Calculate the critical angle for light passing from:

a) glass to air
b) water to air
c) glass to water.

Answer 2

42
49
62

Question 3

Total internal reflection (TIR) requires what two conditions to be met?

Answer 3

• the ray is attempting to emerge from the more dense medium
• the angle between the ray and the normal to the interface is greater than the critical angle.

Question 4

Define diffraction

Answer 4

waves spread out (NOT bend) as they pass an obstacle/pass through a gap/aperture of a size similar to the wavelength.

Question 5

Define refraction

Answer 5

Change in direction of wave (NOT bend) due to change in (optical) density/speed/medium.