Introducing: light
Light is the most important source of information for humans
- there are received and NOT emitted by eyes
(seeing is a passive and not an active process)
- traveling in straight line
- does not necessitate a medium to propagate
- it dissipates when traveling in a medium
- there are mediums in which they cannot propagate
- it was believed to be tinny particles that travel with very high speed
- different in many aspects from sound
Light sources: high temperature objects or gases, excited matter
point-like (a tiny light-bulb), (a)
extended (a neon tube) (b) (each point of it a point-like source)
directed sources (reflectors, lasers)