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Wave Properties


Waves come in many different forms but they all transfer

energy from one place to another. For example:

Seismic waves carry

energy from earthquakes

through the Earth, which

shake the ground.

Sound waves are emitted

from vibrating

loudspeakers making our

eardrums vibrate.

All types of wave are caused by a vibrating source, and

transfer energy without transferring matter. All waves can

be reflected, refracted and diffracted.

What is a wave?


When a group of people in a

stadium decide to start a

Mexican wave, the wave

travels around the stadium.

Mexican waves are an

example of transverse waves.

In a transverse wave, the

particles move up and

down, so the direction of their

movement is at right angles

to the direction of the wave.

Think about the people standing up and down in the same

place as the wave moves around the stadium.

What are transverse waves?


A Slinky can be used to model transverse waves, by moving

one end of the Slinky up and down.

What do transverse waves look like?

The wave travels away from the source. The direction of the

wave makes a right angle with the movement of the source.

source movesup and down

direction of wave

coils vibrateup and down

In a transverse wave, the coils do not travel horizontally;

each coil of the Slinky just vibrates up and down.


Simulation of a transverse wave


What are the parts of a transverse wave?


Investigating transverse waves


The frequency is the number of waves passing any point

each second.

frequency = number of waves past a point / time

frequency is measured in hertz (Hz) = 1/second (1/s)

1 wave per second = 1Hz

If this set of transverse waves pass a point in one second,

what is the frequency? 4Hz

Frequency of transverse waves

1 2 3 4


Frequency is defined as the number of waves per second.

In the example below the frequency is 4Hz.

The time period of a wave is the amount of time it takes for

one wave to pass a point.

time1s

Time period (T) and frequency (f) are related by the equation:

Frequency and time period

orf =1

TT =

1

f

In this example, the time period of the wave is 0.25seconds.

0.25s


Frequency of waves – activity


Sound travels as waves made

by vibrating air particles.

What are longitudinal waves?

PAT ARTWORK PC14_2

Sound waves are an example

of longitudinal waves.

In a longitudinal wave, the

particles vibrate back and forth,

so the direction of their

movement is parallel to the

direction of the wave.

Think about the hairs on this

fluffy cat vibrating backwards

and forwards, as sound waves

from the speaker pass by.


‘Looking’ at sound waves


What do longitudinal waves look like?

A Slinky can be used to model longitudinal waves, by moving

one end of the Slinky left and right.

The wave travels away from the source. The direction of the

wave is parallel to the movement of the source.

source movesleft and right

coils vibrateleft and right

direction of wave

In a longitudinal wave, the coils do not travel horizontally;

each coil of the Slinky just vibrates left and right.


Certain parts of a longitudinal wave have special names.

compression

rarefaction

What are the parts of a longitudinal wave?

Sound waves are longitudinal waves. When someone

speaks, the air particles vibrate as a longitudinal wave and

so compressions and rarefactions are formed in the air.

P waves, the primary waves produced by earthquakes, are

also longitudinal waves, which push and pull the Earth.

Sections that are pushed together are called compressions,

and those that are stretched out are called rarefactions.


Simulation of a longitudinal wave


The wavelength of any wave is the distance between two

matching points on neighbouring waves.

Wavelength of a longitudinal wave

wavelength

wavelength

The wavelength is the same whichever two matching points

are used to measure this distance.

The symbol used to represent wavelength is (lambda).


Transverse or longitudinal waves?


These waves are travelling across

the surface of a pond. The length

of each wave is 0.25m.

From this example, the connection between speed, frequency

and wavelength is:

How is wave speed calculated?

speed = frequency × wavelength

0.5m/s = 2Hz × 0.25m

This means that the waves travel

0.5m each second, so the

speed of the waves is 0.5m/s.

Two waves pass the duck each

second, so the frequency is 2Hz.


Wave speed is measured in metres per second (m/s).

What is the formula for wave speed?

For any set of waves, the wave speed (v) can be calculated

from the frequency (f) and wavelength () using this formula:

What are the units of speed, frequency and wavelength?

Frequency is measured in hertz (Hz).

Wavelength is measured in metres (m).

wave speed = frequency × wavelength

v = f ×


v

×

A formula triangle helps you to rearrange a formula.

The formula triangle for wave speed (v), frequency (f)

and wavelength () is shown below.

Cover the quantity that you are trying to work out, which

gives the rearranged formula needed for the calculation.

So to find frequency (f),

cover up f……which gives the formula…

Can I use a formula triangle?

f =


These waves are rippling

across a pond.

The frequency of the

waves is 0.2Hz and the

length of each wave is

estimated at 0.15m.

What is the wave speed?

Calculating wave speed – example

wave speed = frequency × wavelength

= 0.2Hz × 0.15m

= 0.03 m/s


All electromagnetic waves travel at 300,000,000m/s through a

vacuum. This value is approximately their speed through air.

The speed of electromagnetic (EM) waves

Such large numbers are usually expressed in standard form:

A typical radio station may broadcast

at a frequency of 98MHz. Calculate

the wavelength of this radio wave.

= 3.1m

= v ÷ f

= 3 x 108m/s ÷ 98 x 106Hz

300,000,000m/s = 3 x 108m/s


Wave speed problems


Glossary


Anagrams


Multiple-choice quiz

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