by Jeanette Cain
If you remember from previous articles, reflection makes all nonluminous objects visible, but all objects reflect some light that falls
upon them. The best materials for reflecting light are mirrors, chromium, plate glass, and the surface of water. The surface of a material must be smooth for reflection to occur. The surface of
ground glass is rougher than ordinary glass. Surfaces smooth enough to give good reflections are usually so smooth that you are unable to detect any roughness even with a microscope, meaning the
surface is smooth on a very small scale. If light is a kind of wave and normal reflections only happen with a smooth and small scale, what does it suggest about light wave size? The waves of
light must be extremely small, rather the light waves must have short wavelengths. What is the reflecting surface of a mirror? If you take a piece of broken mirror glass and scrape the coating on
the back, you will see that the coat is a metal, usually silver.
Reflections in a mirror must be reliable, or many accidents would occur, such as the rear-view mirror in a car. This means that there must be some principle, or law of light, allowing it to be
reflected from a shiny surface. It is called the Law of Reflection. It is used by scientists to describe light behavior.
You have the advantage of two eyes, which improves your ability to judge the distance of objects. If you would like to see just how important two eyes are, try this exercise: tape one eye shut
for a while and try to catch a soft rubber ball that you have bounced on the floor. This shows how you use both eyes to look at objects from a distance, so your line of sight is almost parallel.
An object only a foot away will show that the lines of sight are far from being parallel. What is happening? The two lines of sight come together sharply, or converge. Experience has shown
you that when viewing close objects your eyes converge sharply, but, if an object is far away, your line of sight is almost parallel.
Experiment on Reflection
You will need: an adult or friend, a flashlight, a mirror, a pencil, a piece of paper, and a protractor.
1. Shine the flashlight beam into a mirror and observe the light path as it approaches the mirror and again as it moves away from the mirror. This is the way in which you can measure the angle of
the light as it approaches and leaves the mirror.
2. With the point of your pencil, touch the mirror at the point where the reflection is occurring. You may need to adjust your pencil so that it is perpendicular to the mirror's surface.
You will now measure the angle which is between the pencil and the beam of light hitting the mirror. You will also need to measure the angle between the pencil and the beam of light leaving the
What happened? You may wish to try having the flashlight beam hit the mirror at different angles. You will need to measure the hitting angle and the reflecting angle for each one. Did you
discover the relationship between the two angles?
1. Editors. The World Book Encyclopedia. World Book-Childcraft International, Inc: Chicago. 1990
Visible Light Waves
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