1. Review Reflection

2. Topic 3 Refraction

3. Essential Learning Outcome
I can describe the refraction of light through different materials.

4. Law of Refraction
The Law of Refraction states that when light travels from one medium, to a more dense medium, the light will be bent toward the normal, and when it exits the denser medium into a less dense medium it will bend away from the normal. 
The new direction of light is called the angle of refraction.

5. Refraction can also occur when light travels through air at different temperatures, because warm air is less dense than cold air.  The refraction of light through air is called a mirage.  
The pools of water you see on a hot summer day are often caused by this effect, because the air closer to the ground is hotter than the air above it.  As you approach these pools, they disappear - because they were never there.

6. To understand how a mirage forms, one must first understand how light travels through air. If the air is all the same temperature--cold or hot--light travels through it in a straight line. If a steady temperature gradient exists, however, light will follow a curved path toward the cooler air. The standard freshman physics explanation for this phenomenon is that cold air has a higher index of refraction than warm air does. As a result, photons (particles of light) travel through hot air faster than they can through cold air because the hot air is less dense.

7. Is That All There Is To Light?
What happens when light strikes a surface?
Type of behavior
What happens to light striking a surface
Nature of surface
What else happens?
Absorption
Energy Transformation
rough, dark, opaque
some light is reflected
Reflection
Bounces off
smooth, shiny
some light is absorbed
Refraction
Travels through in a new direction
different transparent medium

8. Refraction Diagram

9. http://highered. mcgraw-hill

10. Refraction Diagram
Angles are measured with respect to the line which is perpendicular to the interface.
When light travels from one medium--such as air, to another one of higher density--such as water, usually the light ray bends toward the perpendicular line.

11. Important Terms
Refraction – the bending of light when it travels from one medium (material) to another
Bending Light
When light travels into a more dense material, light bends toward the normal when light travels into a less dense material, light bends away from the normal
Temperature can also bend light  warm air is less dense than cold
Angle of refraction – the angle between the normal & the refracted ray
When light strikes a surface it can be absorbed, reflected, refracted or a combination of all three.

12. One side of wave front slows down, and the entire train of fronts twists.

13. Understanding Refraction