Wavelength is a measure of of the distance from one wave crest to the next. For visual light it is measured in units of thousands of Angstroms (where an Angstrom is one hundred millionth of a centimeter).
Period is a measure of how often something occurs. If your faucet is dripping and a droplet of water falls every ten seconds, then the drip has a period of 10 seconds. If you spin around in circles to make yourself dizzy and you make a full revolution every two seconds, then your spin period is two seconds. When we talk about light we say that its period is how long it takes the wave to travel a full wavelength (the distance from wave crest to wave crest).
Because light always travels at a set velocity, 300,000 kilometers per second,
if you know the wavelength of a beam of light then you know its period as
well. Velocity is equal to distance traveled per unit time, so v = 
÷ P. For light with wavelength , the period P is thus equal to
Let us walk through a simple example, to find the period of a beam of light from its wavelength. If we have green laser pointer, its wavelength is roughly 5500 Angstroms. As we know the speed of light in units of kilometers per second, we'll need to first convert the wavelength from Angstroms into centimeters, and then to kilometers.
and the speed of light c into our relation.
Frequency is the inverse of period. If a wave takes P seconds to complete a single pattern, then it has a frequency of 1/P cycles per second.
is twenty cycles (twenty spins
round the track) per hour. Your house is powered by electricity with a
frequency of 60 Hertz (Hz), which means that the energy in the circuit
oscillates with a period of 0.0167 seconds.
We found above that green light had a period of 1.8 × 10-15 seconds. We can also calculate its frequency.
For light, we can equate the frequency of the beam with the amount of energy that it contains. For light with frequency
, we say the
amount of energy E is proportional to .
We wrote above that energy E and frequency were
proportional to one another (if one increases, so does the other, while if one
drops off in intensity the other will as well). They agree to within a scalar
constant, the constant h which transforms between units of frequency
(cycles per second, or Hz) and units of energy (ergs).
If a beam of light contains 6.63 × 10-27 ergs of energy, it has a frequency of one Hz. How much is an erg? 109 ergs will power a light-bulb for one second (ergs are small!).
Note that because energy correlates with frequency, it is inversely related to period and wavelength. High energy electromagnetic waves have a high frequency, short period, and short wavelength, while low energy counterparts feature a low frequency, a long period, and a long wavelength.
Amplitude is a measure of the height of a wave, the vertical distance from the top of a wave crest to the bottom of a wave trough.
For an ocean wave, you can see the amplitude by watching the height of the wave as it rolls into shore (or listen to the surf report!). For an earthquake wave, watch the ground literally rise and fall at your feet. It takes work to raise water, or to raise up the ground, so it should make sense that a higher amplitude wave also has more energy.