If you went sailing in a boat on the ocean, you would notice that the water was constantly rising and falling in height, making waves. If the weather was calm, you would see smooth, calm, low energy waves. If the weather was stormy, the waves would have been pumped up by the storm into a state of higher energy. You might observe that they were stronger, rose and fell higher (higher amplitude), and that successive waves hit the boat faster and faster (the frequency had increased).

[NMSU, N. Vogt]

• We define wavelength, , as the distance between wave crests (or between any two identical spots along the waves). The units of wavelength are distance units, like meters.

• We define frequency as (or F), the number of times the boat goes up and down per unit time. The units of frequency are 1/(time), like 1/second. Sometimes this is written as cycles/second or Hertz (Hz).

• The period, P or T, is the inverse of the frequency.
  

• We define velocity v, as the speed of the wave. The units of velocity are distance/time, like meters/second.
  

• How much energy, E, does a wave carry? The higher the frequency, or the shorter the wavelength, the more energy the wave has.
  

• The boat goes up and down with the waves. What happens to the water?

• Just what is traveling in the direction of the waves?
  Energy and Information: waves are a disturbance traveling through a medium. In this case, the medium is the water.

What do waves have to do with light?

• We can treat light as a wave. The wavelength, or frequency, of the light determines the amount of energy that it carries. It always moves at a velocity c, the speed of light.