Chapter 22 Reflection and refraction of light
22.1 The Nature of Light
Light generates interference and diffraction patterns (characteristics of a wave).
According to Maxwell, light is a form of electromagnetic wave.
Light can acts like a
particle (the photoelectric effect in Chapter 27). The light particle is called photon, and the energy of a photon
is proportional to the frequency of the electromagnetic wave (f);
E = hf
where h = 6.63 x 10-34 J-s is Plancks constant (Chapter 27).
22.2 Measurements of the Speed of Light (Reading Assignment)
In early days, the speed of light was believed to be infinite.
<Roemers Method>
Roemer estimated the speed of light by studying the eclipses of Io in 1675.
<Fizeaus Method>
Figure 22.2 (using a rotating toothed wheel)
The speed of light is
c = 2.997 924 574 x 108 m/s
22.3 The Ray Approximation in Geometric Optics
Light travels in a straight line path until it encounters a boundary between two different materials.
A Ray of light is an imaginary line drawn along the direction of travel of the light beam.
A wave front is a surface passing through the points of a wave that have the same phase and amplitude. When light rays travel in parallel paths, the wavefronts are planes perpendicular to the rays. (Figure 22.3)
22.4 Reflection and Refraction
<Reflection of Light>
Law of Reflection
The incident ray, the reflected
ray, and the normal to the surface all lie in the same plane, and the angle of
reflection 
equals the angle of
incidence 
: (Figure 22.5)
= 
Specular reflection vs. Diffuse reflection
Example
<Refraction of Light> & 22.5 The Law of Refraction
Figure 22.7
When light strikes the interface between two media, part of the light is reflected and the remainder is transmitted across the interface. The change in the direction of travel as light passes from one medium into another (transmitted light) is called refraction.
Light is refracted because the speed of light is different in the two media.
As light travels from one medium to another, its frequency (f) does not change.
n = 
Also, n = 
where 
is the wavelength of
light in vacuum and 
is the wavelength in
a medium.
Table 22.1 (Indices of refraction for various substances)
Snells Law of Refraction
When light travels
from a material with refractive index n1
into a material with refractive index n2,
the refracted ray, the incident ray, and the normal to the interface between
the materials all lie in the same plane.
The angle of refraction t
2 is related to the angle of incidence 
1 by
n1 sin 
1 = n2 sin 
2 (22.8)
= 
= 
The path of a light ray through a refracting surface is reversible.
Examples
d'
= d (
)
22.5 Dispersion and Prism
The index of refraction in a medium except vacuum depends on the wavelength of light.
Light of different wavelengths is bent at different angles when incident on a refracting material. (Dispersion)
Prism (Figure 22.14 and 15)
22.6 The Rainbow (Reading Assignment)
The rainbow is formed because of the dispersion of sunlight due raindrops.
22.7 Huygenss Principle (Skip)
22.8 Total Internal Reflection
When
light passes from a medium of larger refractive index into one of smaller
refractive index (n1 > n2),
the refracted ray bends away from the normal (
2 > 
1). If the
incident ray is at the critical angle (
1 = 
c ), the angle of refraction (
2) is 90°.
sin 
c = 
for n1
> n2 (22.9)
When
the angle of incidence exceeds the critical angle (
1 > 
c), all the incident light is reflected back into
the medium from which it came, a phenomenon known as total internal reflection.