How things wave

How things wave

Introduction to WAVES.


So - Waves.....  

We spoke about energy.  Energy can, as it turns out, travel in waves.  In fact, you can think of a wave as a traveling disturbance, capable of carrying energy with it.  For example, light "waves" can have energy - like solar energy.  Ocean waves can certainly carry energy.  

There are several wave characteristics (applicable to most conventional waves) that are useful to know:

amplitude - the "height" of the wave, from equilibrium (or direction axis of travel) to maximum position above or below

crest - peak (or highest point) of a wave

trough - valley (or lowest point) of a wave

wavelength (lambda - see picture 2 above) - the length of a complete wave, measured from crest to crest or trough to trough (or distance between any two points that are in phase - see picture 2 above).  Measured in meters (or any units of length).

frequency (f) - literally, the number of complete waves per second.  The unit is the cycle per second, usually called:  hertz (Hz)

wave speed (v) -  the rate at which the wave travels.  Same as regular speed/velocity, and measured in units of m/s (or any unit of velocity).  It can be calculated using a simple expression:





There are 2 primary categories of waves:
Mechanical – these require a medium (e.g., sound, guitar strings, water, etc.)
Electromagnetic – these do NOT require a medium and, in fact, travel fastest where is there is nothing in the way (a vacuum). All e/m waves travel at the same speed in a vacuum (c, the speed of light):

c = 3 x 10^8 m/s

Yes, this is the same speed of light we've talked about already.

First, the electromagnetic (e/m) waves:
General breakdown of e/m waves from low frequency (and long wavelength) to high frequency (and short wavelength):
Radio
Microwave
IR (infrared)
Visible (ROYGBV)
UV (ultraviolet)
X-rays
Gamma rays
In detail, particularly the second image:


We'll spend more time with electromagnetic waves after we first talk about mechanical waves.


Mechanical waves


Mechanical waves include:  sound, water, earthquakes, strings (guitar, piano, etc.)....
Again, don't forget that the primary wave variables are related by the expression:

v = f  l

speed = frequency x wavelength


 (Note that l should be the Greek symbol 'lambda'.  See the boxed equation above.)

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