What would the world be without light? Go into a dark room and cover your eyes with your hands. open your eyes wide. What do you see? Nothing. What you just did shows that without light entering your eyes you could not see anything.
Now go into a room that is brightly lighted. What re the brightens things in this room? The electric light bulbs in lamps or in light fixtures. Or fluorescent light tubes. These things are making the light that is in the room. Things that make light are called light sources.
Go out of the houses. Do you see any light sources? If it is day, you see a big one-the sun. If it is night, you see light coming from the streetlights and, maybe, from advertising signs. If the sky is clear, you see thousands of stars. All of these things are light sources- they make their own light. The sun is white-hot and sends out a tremendous amount of light. The stars are suns very far away from the earth. If the streetlights you saw had electric light bulbs, the light source inside them was a thin wire made a glow white-hot by sending electric current through it. Or streetlights may have had florescent lamps, which are filled with a kind of gas that causes the lamp to glow when electric current is sent through it.
What about the moon- is it a light source? And a planet Venus, which shines like a bright stars? The moon, Venus, and other planets shine because form the sun strikes them and then bounces to the earth- to your eyes.
Go back into the house. Look at all the things you can see that are not light sources. You see them because light the sources strikes them and bounces off them your eyes- the way a rubber ball bounces off a wall. Bounced light is called reflected light.
Things with smooth surfaces reflect more light that others. The light that is more reflected is absorbed. An object that reflects no light- that absorbs it all- looks black. Between those things that reflect all light and those absorb all light are things we see in different shades. The light shade of blue that is like a robin's egg reflects more light than the dark shade of blue that is like a sailor's navy blue uniform. The navy absorbs more light
Light travels in straight lines. That is why can't see around a corner.
Throughout history many scientist have had ideas or theories about what light is. In the early part of the 20th century a scientist named Max Planck put forth a theory that light is made up of extremely tiny bundles of energy called photons. Bundles of photons are called light rays. The rays travel away from a light source in the same way rings of the water move away from the place where a stone strikes the surface of water. Light rays travel in straight lines. This is a very important about light.
No comments:
Post a Comment