# Representing waves. There are two ways we can represent a wave in a graph;

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Representing waves

There are two ways we can represent a wave in a graph;

Displacement/time graph This looks at the movement of one point of the wave over a period of time 1 Time s -2 0.10.20.30.4 displacement cm

Displacement/time graph This looks at the movement of one point of the wave over a period of time 1 Time s -2 0.10.20.30.4 displacement cm PERIOD

Displacement/time graph This looks at the movement of one point of the wave over a period of time 1 Time s -2 0.10.20.30.4 displacement cm PERIOD

Displacement/time graph This looks at the movement of one point of the wave over a period of time 1 Time s -2 0.10.20.30.4 displacement cm PERIOD IMPORTANT NOTE: This wave could be either transverse or longitudnal

Displacement/distance graph This is a “snapshot” of the wave at a particular moment 1 Distance cm -2 0.40.81.21.6 displacement cm

Displacement/distance graph This is a “snapshot” of the wave at a particular moment 1 Distance cm -2 0.40.81.21.6 displacement cm WAVELENGTH

Displacement/distance graph This is a “snapshot” of the wave at a particular moment 1 Distance cm -2 0.40.81.21.6 displacement cm WAVELENGTH

Displacement/distance graph This is a “snapshot” of the wave at a particular moment 1 Distance cm -2 0.40.81.21.6 displacement cm WAVELENGTH IMPORTANT NOTE: This wave could also be either transverse or longitudnal

Wave intensity

This is defined as the amount of energy per unit time flowing through unit area It is normally measured in W.m -2

Wave intensity For example, imagine a window with an area of 1m 2. If one joule of light energy flows through that window every second we say the light intensity is 1 W.m -2.

Intensity at a distance from a light source I = P/4πd 2 where d is the distance from the light source (in m) and P is the power of the light source(in W)

Intensity at a distance from a light source I = P/4πd 2 d

Sound intensity The lowest intensity that can normally be heard by a human ear is 1 x 10 -12 W.m -2 This is a sound intensity level of 0 dB

Intensity and amplitude

The intensity of a wave is proportional to the square of its amplitude I α a 2 (or I = ka 2 )

Intensity and amplitude This means if you double the amplitude of a wave, its intensity quadruples! I = ka 2 If amplitude = 2a, new intensity = k(2a) 2 new intensity = 4ka 2

Surfers know this!

Let’s try some more questions!

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