Representing waves

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

-1

-2

0.1 0.2 0.3 0.4

displacement

cm

Displacement/time graph

This looks at the movement of one point of the wave over a period of time

1

Time s

-1

-2

0.1 0.2 0.3 0.4

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

-1

-2

0.1 0.2 0.3 0.4

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

-1

-2

0.1 0.2 0.3 0.4

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

-1

-2

0.4 0.8 1.2 1.6

displacement

cm

Displacement/distance graph

This is a “snapshot” of the wave at a particular moment

1

Distance cm

-1

-2

0.4 0.8 1.2 1.6

displacement

cm

WAVELENGTH

Displacement/distance graph

This is a “snapshot” of the wave at a particular moment

1

Distance cm

-1

-2

0.4 0.8 1.2 1.6

displacement

cm

WAVELENGTH

Displacement/distance graph

This is a “snapshot” of the wave at a particular moment

1

Distance cm

-1

-2

0.4 0.8 1.2 1.6

displacement

cm

WAVELENGTH

IMPORTANT NOTE: This wave could also be either transverse or longitudnal

Wave intensity

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 1m2. 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/4πd2

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/4πd2

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

Intensity and amplitude

The intensity of a wave is proportional to the square of its amplitude

I α a2

(or I = ka2)

Intensity and amplitude

This means if you double the amplitude of a wave, its intensity quadruples!

I = ka2

If amplitude = 2a, new intensity = k(2a)2 new intensity = 4ka2

Surfers know this!

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