Properties of Waves
External Links page.
What Do We Easily See about
- What kinds are there? We can
see different colors, and there are other types that we can't
- How does it affect matter? Light
can come out of matter, or be absorbed, reflected, transmitted;
It carries heat-energy.
- How does it move? Apparently
instantaneously, in reality at 300,000 km/sec! It travels in
straight lines, except...
A Few Notions about Waves
- Waves: Period, wavelength, amplitude,
frequency, velocity or speed; Related by velocity = (wavelength)
- Examples: Waves in water, strings
(transverse); Sound (longitudinal); light.
- How can we tell if something is a wave?
Interference and diffraction (like when looking through fogged
What Are Light
- Electromagnetic waves: Made
of changing electric and magnetic fields.
- Different types: Colors depend
on wavelength; but visible light is only a small part of the
- Different effects: Which ones
make it through the atmosphere? Which ones can our bodies detect?
- Why are we interested in detecting
waves of different wavelengths? Some objects don't emit
much visible light; Visible light cannot traverse certain regions;
and different kinds of radiation provide different kinds of information.
Different Types, Based on Wavelength
* A star indicates a type of radiation that can traverse
the Earth's atmosphere relatively easily.
Type and Wavelength
Examples; Common Sources
Sources and Uses in
|Radio * (l
from mm's to 1000's of m)
||Radio, TV; Antennas
||Radar studies of planets; Interstellar gas clouds;
Active galaxies and galactic structure
from mm's to cm's)
||Cell phones; Ovens
||Cosmic background radiation
|Infrared * (l
from microns to mm)
||Communications, remote controls; Warm objects
||Interstellar dust and star forming regions; Cool
|Visible * (l
from 400 to 700 nm)
||Ordinary light; Hot objects
||Solar system planets; Stars; Galaxies
from 10–9 to 10–7
||Solar radiation; Atoms
||Hot stars; Interstellar medium
|X-rays (l from
10–11 to 10–8
||Medical applications; Atoms
||Stellar atmospheres; Neutron stars and Black
holes; Galaxy clusters; Active galactic nuclei
less than 10–11 m)
|Medical applications; Nuclear reactions
||Neutron stars, cosmic ray collisions; Active
galactic nuclei; Gamma Ray Bursts.
What Can We
Learn from Analyzing Light?
- Distance effect: Inverse square
law for brightness. Conclusion:
Compare apparent brightness with actual one to get the distance!
- Velocity effect: Doppler shift
of wavelengths or frequencies from radial motion. Conclusion:
Check the wavelength to get the velocity along the line of sight!
- Can we get more information?
Some sources emit only at a few specific wavelengths, others
at all wavelengths. We need to know which ones, and what affects
the amount of light we get at each wavelength.
So, light is a wave,
but we will see that this is not the end of the story...
Examples of Uses of Different
Types of Radiation
- Infrared: Asteroids (the amount
of infrared radiation tells us how much sunlight they absorb,
thus their albedo, and helps us find their size even if we cannot
resolve it with a telescope).
page by luca bombelli <bombelli at olemiss.edu>,
modified 10 sep 2012