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 right to left,  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 video below shows a summary of the above wave basics:

Wave Formulas

The following formulas will be used in this section to describe waves:-

Where :-

f = Frequency (Hz)

n = Number of Waves (s)

t = Time (s)

λ = Wavelength (m)

v = Wave Speed (m/s)

d = Distance travelled (m)

T = Period (s)  

Example 1 - 

A car horn  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