Review Reflection http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/optics/lr.html

Topic 3 Refraction

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

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.

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.

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.

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

Refraction Diagram

http://highered. mcgraw-hill http://highered.mcgraw-hill.com/sites/0072414944/student_view0/chapter8/animations.html#

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.

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.

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

Understanding Refraction