What is a Wave ?
There are lots of examples of waves that can be seen in the World around us. Some examples are shown below:-
Waves might have many different forms, but they have one main feature:-
"Waves are a transfer of Energy"
In a wave, it is only Energy that moves, the medium (the material the wave is passing through) just oscillates back and forth around an equilibrium point. In the animation below, a wave is moving from left to right, it can be seen that the medium simply oscillates up and down:-
All waves can be described in one of two ways:-
1. Transverse Waves - In a transverse wave, the medium oscillates perpendicularly to the movement of the Energy.
2. Longitudinal Waves - In a longitudinal wave, the medium oscillates parallel to the movement of the Energy.
The diagram below shows examples of each type:-
Parts of a Wave
The main parts of a wave are shown in the diagram below:-
Wave Part Definitions
Wavelength (λ) - The Wavelength is the distance between any two repeating points of a wave (usually between two peaks), measured in meters (m).
Amplitude - The Amplitude is the distance between the equilibrium point and a peak or trough, measured in meters (m).
Frequency (f) - The Frequency of a wave is the number of waves passing a fixed point in one second, measured in Hertz (Hz).
Wave Speed (v) - The Speed of a wave is a measure of how fast a wave is travelling, measured in meters per second (ms−1).
Period (T) - The Period of a wave is the time taken for a single wave to pass a fixed point, measured in seconds (s).
The following formulas will be used in this section to describe waves:-
Example 1 -
A car horn of produces 1500 waves in three seconds. Calculate:
1. The Frequency.
2. The Period.
f = n / t
f = 1500 / 3
f = 500 Hz
T = 1 / f
T = 1 / 500
T = 0.002 s
Example 2 -
A sound wave has a Frequency of 850 Hz and a Wavelength of 0.4m.
Calculate the Speed of the wave.
v = f λ
v = 850 x 0.4
v = 340 ms−1
Example 3 -
A boat sails on a rough sea. The Frequency of the waves is 0.25 Hz, with a wavelength of 12 m. If the boat is 60 m long, how long does it take the wave take to pass under the boat?
v = f λ
v = 0.25 x 12
v = 3 m s−1
v = d / t
t = d / v
t = 60 / 3
t = 20 s