Wave Basics

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).

Wave Formulas

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.


1.

f = n / t

f = 1500 / 3

f = 500 Hz


2.

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