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REFRACTION
is the changing of direction of a ray of light as it travels from one medium to another.
3. Lenses
http://en.wikipedia.org/wiki/File:GGB_reflection_in_raindrops.jpg
We have learned before that light travels in straight lines, commonly called rays.
So why do they bend ?
Look the diagram on the right.
You may see two go-carts, both of which are rolling downhill on a road.
They will soon come to a mud slick across the road.
What do you think will happen the carts as they hit the mud.
What will happen to the velocities of both cars ?
Will anything happen the direction of their motion ?
When the carts make it through the mud slide, what do you think will happen the velocities of the carts then ?
oh yeah and their directions ???
give it a think
the one going straight towards the mud will slow down and pass through on the line that it entered.the go-cart that hits the mud at an angle, its front right wheel will hit the mud first and therefore this wheel will travel slower than its opposite left wheel.
Then the left wheel goes in the mud and it will continue at its new angle
until the front right wheel will again hit the road. At this time the right wheel will be going faster than the left one and so the go cart will turn away from the straight line path.
This is very analogous to refraction (especially if you omit the 2nd axle)
As light (or the cart) enters a medium that slows down its speed the ray will turn towards the normal.
As light leaves a medium that slows down its speed the ray will turn away the normal.
3. Lenses
Need a page or section on Dispersion
red light deviated least in a prism and deviated the most in a grating (or equivalent) (3)
wheras the refractive index for red ligjt in glass is 1.51 and for violet is 1.53 so violet refracts more on entering a prism and so the red light is deviated LEAST by the prism hence the colours are dispersed
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