You need to know about these quantities used in waves - what they mean, the symbols used for them and the units used to measure them.
The amplitude ( ) of a wave is the distance from the centre line (or the still position) to the top of a crest or to the bottom of a trough. Be careful with this quantity - the centre line is not always given in a diagram. Amplitude is measured in metres ( ). The greater the amplitude of a wave then the more energy it is carrying.
The wavelength, , of a wave is the distance from any point on one wave to the same point on the next wave along. (The symbol is a Greek letter, 'lambda'.) To avoid confusion, it is best to measure wavelength from the top of a crest to the top of the next crest, or from the bottom of a trough to the bottom of the next trough. Wavelength is also measured in metres ( ) - it is a length after all.
The frequency( ) of a wave is the number of waves passing a point in a certain time. We normally use a time of one second, so this gives frequency the unit hertz ( ), since one hertz is equal to one wave per second.
Don't get confused with this quantity frequency. It is not a distance travelled by waves, nor is it a speed, although it is linked to both of these quantities. For water waves and sound waves the unit hertz is usually good enough but radio and TV waves have such a high frequency that the kilohertz ( ) or even the megahertz ( ) are better units.
The speed (or sometimes you might see it called velocity) of a wave ( ) is how far the wave travels in a certain time.
Wave speed is measured in metres per second ( ).
All the electromagnetic waves travel at 300,000,000 metres per second ( ). Sound travels at about 340 metres per second.