Download Critical angle - Kelso High School

Revision
1. Sketch a wave and mark on it the wavelength and amplitude.
2. What is meant by the frequency of a wave and give its unit?
3. Define the period of a wave?
4. Give two equations to calculate the velocity of a wave.
5. What is refraction?
6. Draw a diagram of a light wave being refracted, going from
air into glass. Mark on the normal, the incident and refracted
angles.
7. Draw a diagram showing reflection. Mark the normal and the
angles of incidence and reflection.
8. What is total internal reflection? Draw an optical fibre
showing this.
6. Draw a diagram of a light wave being refracted, going from
air into glass. Mark on the normal, the incident and refracted
angles.
7. Draw a diagram showing reflection. Mark the normal and the
angles of incidence and reflection.
8. What is total internal reflection? Draw an optical fibre
showing this.
9. What is the critical angle?
10. What is diffraction? Why do radio waves diffract around hills
that block TV waves?
11. Waves have the following properties – reflection, diffraction,
refraction and interference. Can particles be reflected,
diffracted and refracted? We will find out about interference in
this unit.
Tutorial questions p61 Qu 1 to 4 SAQs page 1 to 6
Law of refraction – Snell’s Law
1 angle in air
2 angle in material
1
2
1
2
sin 2
2
1
sin 1
sin 1  sin 2
sin 1 = n sin 2
n = sin 1
sin 2
n – refractive index of a material
The refractive index of a vacuum is 1, for gasses it is almost 1.
n has no units.
n is always greater than 1
Always take 1 to be the angle in vacuum (or air)
Find the refractive index of plastic and if you have time repeat the
experiment to get the refractive index of glass.
Critical angle
NB: The angle in air, 1, is always bigger than in the other
material.
For the critical angle 1 = 90o
Sin 90o = 1
n=
1
2
1
sin c
Expt Find the critical angle of plastic and glass and use this to
calculate their refractive indices.
Tutorial questions 18 and 19
NB. The frequency of the light is unchanged when it is refracted.
( i.e. it stays the same colour).
A higher frequency of light has a higher refractive index. i.e. blue
light bends more than red.
White light
prism
n = sin 1 = v1 = 1
sin 2
v2
vacuum (air) is 1
2
Tutorial questions 20 to 28 Revision Ex 8.4, 8.5