1. THE RAY MODEL OF LIGHT
Section 11.4

2. Light Travels In A Straight Line
This fundamental property of light can be used to understand how light behaves when it strikes a mirror or lens.

3. A Light Ray
A luminous object (e.g. Candle) radiates light in all directions.
Spherical Illumination
You can illustrate this easily using a light ray diagram.

4. Light Ray
A light ray is a line and arrow that represents the direction and straight- line path of light.

5. Light Rays

6. Geometric Optics What is geometric optics?
The use of light rays to determine the path of light when it strikes an object.

7. Incident Light
Light emitted from a source that strikes an object.

8. TRANSPARENT When a material transmits all or almost all incident light
Objects can be clearly seen through the material.

9. TRANSLUCENT
When a material transmits some incident light but absorbs or reflects the rest.
Objects are not clearly seen through the material

10. OPAQUE When a material does not transmit any incident light.
All incident light is either absorbed or reflected.
Objects behind the material cannot be seen at all.

11. FLAT MIRROR
An image is a reproduction of an original object that is produced through the use of light.

12. Mirror
A mirror is any polished surface that exhibits reflection.

13. Reflection
Reflection is simply the bouncing back of light from a surface.

14. Regular Reflection - Reflection off a smooth, shiny surface
In regular reflection, when a series of parallel incident rays strike a flat reflective surface, all the angles of incidence will be the same. This means all the angles of reflection will be the same, and thus the reflected rays will also be parallel.
- Reflection off a smooth, shiny surface

15. Diffuse Reflection Reflection off an irregular, rough, or
When parallel incident rays are directed at an irregular surface, all the incident rays will have different angles of incidence. This means all their angles of reflection would also be different. The reflected rays will not emerge parallel to one another, but will be scattered in different directions.
Reflection off an irregular, rough, or
dull surface making the rays scatter
in different directions

16. Regular vs. Diffuse Reflection

21. Ray Diagram
- Shows how a single ray bounces off a mirror or other smooth surface
Normal
Reflected Ray
Incident Ray
Angle of Incidence (θi)
Angle of Reflection (θr)

22. Ray Diagrams Incident Ray
An incoming ray that travels from a light source toward a surface
Normal
The line that is perpendicular to the surface where a ray of light meets the surface
Reflected Ray
A ray that bounces off the surface and begins at a point where the incident ray and the normal meet
Angle of Incidence (θi)
Angle between the incident ray and the normal
Angle of Reflection (θr)
Angle between the reflected ray and the normal

23. Laws of Reflection The angle of incidence equals the angle of
reflection (θi = θr)
The incident ray, the reflected ray, and the
normal all lie on the same plane

24. Ray Diagrams Draw the normal (perpendicular to the mirror)
62°
62°
Draw the normal (perpendicular to the mirror)
Measure the angle of incidence
Draw the ray of reflection (same angle as angle of incidence)

25. Homework:
Read Chapter 11.5
Questions:
#1, 2, 3, 4, 5, 6

26. Important Terms
The ray of light which strikes the surface is called the incident ray.
The ray of light which leaves the surface is called the reflected ray.
A line perpendicular to the surface is imagined at the point of reflection. This line is called a normal. In this context the word normal means perpendicular.
The angle between the incident ray and the normal is called the angle of incidence, or the incident angle.
The angle between the reflected ray and the normal is called the angle of reflection, or the reflected angle

27. How can we predict how we see images or where we will see them?
RAY MODEL of LIGHT: makes the assumption that light travels a straight-line path as long as it is unhindered. 
The RAY is an ideal extremely narrow beam of light.  To look at something stationary at different angles would translate into your eye “catching” different rays as you moved your head. 
In the ray model of light, one treats light as if it were a particle. 
It describes REFLECTION, REFRACTION, and IMAGE FORMATION by mirrors and lenses.

28. WHAT HAPPENS WHEN LIGHT HITS an OBJECT?
Light can be ABSORBED and transform into THERMAL ENERGY (Think of that dark colored shirt on a hot day…)
Light can be TRANSMITTED through the object if the material is transparent. (Think of that glass of water on a hot day…)
Light can be REFLECTED (or bounced off and object)

29. Smooth vs. Rough Surfaces
On smooth surfaces, the reflection is known as specular. (Speculum = mirror (latin))  Your eye must be in the right place to receive the image.
On rough surfaces, the reflection is known as diffuse. Light hits the surface at different angles so it will bounce in different directions and no matter where you are you will see some of reflected light even if the rays are not the same.