When light hits an object, it is either reflected, refracted, or both. When light is reflected, it bounces off the surface at the same angle (the angle of reflection) that it came in (the angle of incidence). This is called the Law of Reflection.

Light can also be refracted. The light hits the surface and bends, so it leaves the surface at a different angle. This happens when light is travelling from one medium to another. For example, when light goes from air into water, it is refracted. Why? Because the light moves at different speeds through different materials. If you've ever looked down at your feet when you're in a swimming pool, you might have noticed that they look strange. The light is moving from air to water, so it refracts off your feet, making them look funny.

• 1 small piece of black or dark blue construction paper
• 1 bottle of clear nail polish (use only 1 drop per pin)
• 1 small, shallow dish (such as a pie plate)
• 1 safety pin
• scissors
• tape
• water

1. Put about an inch of water in the bottom of the small dish.
2. Put your small piece of construction paper into the dish, making sure that the whole thing is submerged and soaked with water.
3. Place a drop of nail polish in the water, over the construction paper, and take the construction paper out.
4. Let the construction paper dry completely.

2nd session

1. Cut your construction paper in any shape that you wish.
2. Tape a safety pin to the back...you are now done.

To work your rainbow pin:

• Hold it up to a source of light, and angle it in different directions. Can you see the rainbow?

Why does this happen? Some of the light rays are reflected by the surface and some of the rays go through and are reflected off the bottom of the film. When the reflected rays overlap as they leave the film, some of them cancel each other out. (This is called interference.) The colour that you see is a mixture of what's left over. At another place where the nail polish is thinner, a different colour may be cancelled out. That's why you see different colours coming from different places on your pin.

You can see the same phenomenon when light reflects off a soap bubble, or off a puddle of gasoline on a wet street. This effect is called Thin Film Interference.