Unit+2+Refraction+of+light

What causes light to refract?
Light changes speed as it enters from one medium to another and bends. The bend of light depends on the refractive index of the medium. Different mediums have different refractive index and density.

These images shows the refraction of light:

http://www.dkimages.com/discover/Home/Science/Physics-and-Chemistry/Sound-and-Light/Light-Waves/Light-Waves-023.html

The light bends as it passes from air to water. http://webphysics.davidson.edu/faculty/dmb/EdibleOpticalMaterials/glass_of_water.jpg

A prism refracts light at different directions to form a rainbow. ROYGBV http://www.hegel.net/en/gif/prism-and-refraction-of-light-into-rainbow-2-AJHD.jpg

The diagram below shows the refraction of light when it passes from one medium to another. The red line is the normal, which is perpendicular to the surface of the medium. As the light passes through the second medium, the light bends towards the normal because density of the second medium is greater than the first. The angle between the incoming ray and the normal is the angle of incidence. The angle between the refracted ray and the normal is the angle of refraction.

http://www.datasync.com/~wizard/Lasers/Refraction348.jpg

=
Converging (convex) lens is thicker in the middle, and as the light rays pass through, they converge (meet) at one point.
 * Use the optical bench applet to help you distinguish between a converging (convex) and diverging (concave) lens **======

Below shows an image of the optical bench applet with beams (many parallel light rays) passing through the convex lens.

[|Optical Bench Applet]

Diverging (concave) lens is thinner in the middle, the lens curves in. As the light rays pass through, they diverge (spread out), the rays do not meet like the convex lens.

Below shows an image of the optical bench applet with beams (many parallel light rays) passing through the concave lens.

[|Optical Bench Applet]

What causes mirage?
Mirage usually forms when the weather is hot. The density of hot air is less than the density of cool air. As light travels through the air, it changes speed as it gets closer to the ground due to the hot air from the ground. The light bends away from the normal. It keeps on bending as it gets closer to the ground until it head towards the opposite direction and travels into our human eyes. but our human eyes assume the light travels in a straight line, so we thought that the object is on the ground, but the object that we see is actually an image that refracts into our eyes.

http://upload.wikimedia.org/wikipedia/commons/thumb/4/42/Pavement_Mirage_Diagram.svg/650px-Pavement_Mirage_Diagram.svg.png

This is an image of mirage on a driveway:

We see lightning before we hear thunder because light travels much faster than sound. Light travels at 299,729, 485 miles per second and sound only travels at 340 miles per second. The speed of light is approximately 881,500 times faster than the speed of sound, and thus lightning is visible to our eyes before we hear claps of thunder during a storm.
 * 8. Explain why you see lightning before you hear thunder. **

For more information, check out these pages on the speed of light and sound. [|The Speed of Light] and [|Speed of Sound & Wave Speeds]