What is a Light Ray?
There are 4 preliminary ideas you need to understand about light
- Some things emit light rays, and some don't.
- Things that emit light rays are called
- An object can be luminous because it is very
hot (incancescent), or
- An object may be luminous due to chemical/electrical
- Light rays travel in straight lines until they hit
- 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
- 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
"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 (firstname.lastname@example.org)