Reflection and Refraction
Chapter 29
Reflection

When a wave reaches a boundary
between two media, some or all of
the wave bounces back into the first
medium.
Reflection
The angle of
incidence is equal
to the angle of
reflection" is one
way of stating
the law of
reflection for light
in a plane mirror.
Reflection
Law of
Reflection:
the angle of
incidence
equals the
angle of
reflection
Reflection
Consider the diagram at the
right. Which one of the angles
(A, B, C, or D) is the angle of
incidence? ______ Which one
of the angles is the angle of
reflection? ______
Reflection
A ray of light is incident towards a plane mirror at
an angle of 30-degrees with the mirror surface.
What will be the angle of reflection?
Reflection
Perhaps you have observed the image of the sun in
the windows of distant buildings near the time that
the sun is rising or setting. However, the image of
the sun is not seen in the windows of distant
building during midday. Use the diagram below to
explain, drawing appropriate light rays on the
diagram.
Reflection
A ray of light is approaching a set of three mirrors as shown in the
diagram. The light ray is approaching the first mirror at an angle
of 45-degrees with the mirror surface. Trace the path of the light
ray as it bounces off the mirror. Continue tracing the ray until it
finally exits from the mirror system. How many times will the ray
reflect before it finally exits?
Reflecting Mirrors


In order to see the image of an object in a
mirror, you must sight at the image; when you
sight at the image, light will come to your eye
along that line of sight.
The image location is thus located at that
position where observers are sighting when
viewing the image of an object
Reflecting Mirrors

It is the location behind the mirror where
all the light appears to diverge from
Reflecting Image Location
Image Formation in
Plane Mirrors
Image Formation in
Plane Mirrors
But what if the man stood a different distance
from the mirror? Wouldn't that cause the man
to need a different amount of mirror to view
his image? Maybe less mirror would be
required in such an instance?
Image Formation in
Plane Mirrors
Diffuse Reflection
Rough surface, diffuse reflection
Diffuse Reflection
Diffuse Reflection
Rough surfaces consist
of a large number
of different specularlyreflecting planes.
Visible light reflects
diffusely from
paper.
Diffuse Reflection
Rough surfaces seem
smooth
for very long-wavelength
electromagnetic waves.
This parabolic dish reflects
long wavelength radio
waves
to the detector, but reflects
most of the shorter
wavelength
radiation away from the
detector.
Reflection of Sound
Reflected Wave
Incident Wave
Reflection of Sound
spherical wavefronts reflected as if there were an "image" of
the sound source at the same distance on the other side of
the wall.
Reflection from Concave
Surface
Any concave surface will tend to focus
the sound waves which reflect from it
Refraction
Refraction
is the bending of light as it passes between
materials of different optical density.
Index of Refraction of a material is the ratio of
the speed of light in vacuum to the speed of light
in that material:
n=
c/v
where v is the speed of light in the material.
Refraction
n=
c/v
•the more dense the material, the slower the
speed of light in that material. Thus n > 1 for all
materials, and increases with increasing density.
n = 1 in vacuum.
Refraction
•The frequency of light does not change when it
passes from one medium to another. According to
the formula v =  f , the wavelength must change.
The index of refraction can therefore be written in
terms of wavelengths as:
n=
where 0 is the wavelength of the light in the
vacuum and  is the wavelength of the light in the
medium.
Refraction
Light in air incident on
glass surface where it is
partly reflected at the
interface and partly
transmitted into the glass.
The direction of the
transmitted ray is changed
at the air/glass surface.
The angle of refraction r is
less than the angle of
incidence i.
Refraction
The velocity of visible light in different
media. The value of 100% refers to the
velocity of light in vacuum.
Refraction
Light waves of wavelength  incident on
glass change direction and wavelength
when transmitted into the glass.
Refraction of Light
The greater the change in velocity and
wavelength, the greater the change in
direction
Refractive Index
For light, the index of refraction n equals the
ratio of the velocities of light in vacuum (c) to
that in the medium (v), that is n = c/v.
Medium
Refractive Index
Air
1.0003
Water
1.33
Linseed
1.48
Oil
Co Green
2.00
Diamond
2.42
Ti White
2.5
Light in Glass
Light incident on a glass plate. The reflected
part of the ray is shown along with the light
path for the refracted component.
Total Internal Reflection
If light is inside a material such as glass with a
larger refractive index n2 than that n1 of the
material outside such as air, there is an angle,
the critical angle of incidence, beyond which
the light is reflected back into the material and
does not escape
sin ic = n1 / n2
Critical Angle
For light exiting glass,
n2 = 1.5, the relation becomes
sin ic = 1.0 / 1.5
the value of the critical angle of incidence is
41°
Total Internal Reflection
The internal reflectance at an air/glass interface for light rays from a point source
in glass. Light rays incident at angles to normal at greater than the critical angle
(here, 41° for glass to air) do not leave the material and are reflected at the
glass/air interface
Refraction of Sound
Refraction of Sound