What is a Light Ray?

There are 4 preliminary ideas you need to understand about light rays:

  1. Some things emit light rays, and some don't.
    1. Things that emit light rays are called luminous objects
      1. An object can be luminous because it is very hot (incancescent), or
      2. An object may be luminous due to chemical/electrical processes (fluorescent)
  2. Light rays travel in straight lines until they hit something.
  3. When a light ray hits something, part of it usually bounces off (reflection), part of it is absorbed, and if it hits something transparent, part of it continues on its way (refraction).
  4. You can't see a light ray unless it gets into your eye.

Usually beginning physicists only have trouble believing the last statement above - your teacher can show you some things that might convince you.

"Bouncing" is not a very dignified thing for a physicist to be talking about, so physicists call it reflection. Reflection is the topic of this section, and is covered in the text in sections 29.1 - 29.5. Light traveling into a transparent medium is called refraction, and refraction is the topic of sections 29.6 - 29.12 in the text. The part of the light ray that is absorbed by a substance is usually converted to heat energy, which is discussed in Unit 3 in the text.

last update September 2, 1999 by JL Stanbrough (jstanbro@venus.net)