1. The angle of incidence is equal to the angle of reflection
LAW OF REFLECTION
The behavior of light as it reflects off a mirror follows the Law of Reflection
At the point of incidence where the incident ray strikes the mirror, a line (Normal) can be drawn perpendicular to the surface of the mirror
Angle between the _____________________ and normal is the angle of incidence θ(i)
Angle between the ____________________ and normal is the angle of reflection θ(r)
The law of reflection states that when a ray of light reflects off a surface:
The angle of incidence is equal to the angle of reflection =
Eye

2. DRAWING RAY DIAGRAMS FOR PLANE MIRRORS
For each line of the object:
Draw a reference line from the base of the object perpendicular to the mirror and extend it (use dashed lines) behind the mirror
Draw a ray from the top of the object perpendicular to the mirror and extend it (use dashed lines) behind the mirror. It will be parallel to the reference line.
Draw a ray from the top of the object to the point where the reference line meets the mirror
Draw the reflected ray according to the law of reflection
Extend the reflected ray behind the mirror (use dashed lines) until it intersects the ray from the top of the object. This is the top of the image O
Object
Mirror

3. POSITION OF THE IMAGE
Each sight line can be traced backwards beyond the mirror
All sight lines (viewers) will intersect at the image location
The image is therefore formed at the single point on the opposite side of the mirror from where all the light rays appear to have diverged
Viewer 1
Object
Viewer 2
Viewer 3

4. PRINCIPLES OF REFRACTION
MEDIUMS: substances that light can move through (water, glass, air)
REFRACTION: Light travels at different speeds in different mediums. Light bends when it moves from one medium to another if they have different densities
NORMAL: An imaginary line perpendicular to the point of incidence
For mediums of different densities
θ(r) ≠ θ(i); for θ(r) ≠ 0 º
Angle of
Incidence
Incident Beam
θ(i)
Medium 1
Medium 2
Angle of
Refraction
θ(r)
Refracted Beam
Example:
θ(i) [air] = 56 º
θ(r) [water] = 38.2 º

5. REFRACTION OF LIGHT BETWEEN MEDIUMS
How can you predict whether light bends towards or away from the normal ?
Light traveling from a less dense medium to a more dense medium, light bends TOWARDS the normal
Light traveling from a more dense medium to a less dense medium, light bends AWAY from the normal
Less Dense
More Dense

6. INDEX OF REFRACTION (n)
Speed of light in a vacuum (c)
Speed of light in another medium (v)
n = number of times slower that light travels in a medium relative to its speed in a vacuum
Light travels slowly in a medium with a high density (v)
Mediums with high density have high index of refraction (n)
Light will refract more in a high density, slow medium
Medium Index of Refraction (n)
Vacuum
Air
Ice 1.31
Water
Ethyl Alcohol 1.36
Plexiglas 1.51
Crown Glass 1.52
Light Flint Glass 1.58
Dense Flint Glass 1.66
Zircon
Diamond
Gallium Phosphide 3.50
Optical Density
Increasing

7. Applications of Refraction
Inferior Mirages
Occur when cooler layers of air lie above warmer air (close to ground!)
The index of refraction of air decreases from sky to ground
As light travels downwards, it refracts away from the normal
Light is eventually totally internally reflected upward from one of the layers
We perceive a reflective (shiny) surface, which is actually an image of the sky reflected upward “from the road”.
Why does the road look wet in this photograph?

8. SNELL’S LAW θ1 θ2 SNELL’s LAW n1.sin(θ1) = n2.sin(θ2)
Snell's law gives the relationship between the angles of incidence and refraction for light impinging on an interface between two mediums with different indices of refraction θ1 n1 n2 θ2
SNELL’s LAW
n1.sin(θ1) = n2.sin(θ2)