9. Wave Properties v2.0

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When the surface of this lake is disturbed, waves spread out across the surface of the water.

What are transverse waves?

Water 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 this boat bobbing up and down in the same place as the water waves pass by!


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 is at right angles to 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.


Water waves and electromagnetic waves, such as light, are examples of transverse waves.

Certain parts of a transverse wave have special names.

What are the parts of a transverse wave?

peak

trough

The high points of a transverse wave are called peaks and the low points of a transverse wave are called troughs.

S waves, the secondary waves produced by earthquakes aretransverse waves, which shake the Earth from side to side.


Simulation of a transverse wave


The wavelength of any wave is the distance between two matching points on neighbouring waves.

Wavelength of a transverse wave

The wavelength is the same whichever two matching points are used to measure this distance.

wavelength

wavelength

wavelength

The symbol used to represent wavelength is .


The amplitude of any wave is the maximum distance a point moves from its rest position.

Amplitude of a transverse wave

The amplitude of a transverse wave is the height of a peak or trough from the wave’s rest position of the wave.

amplitude

amplitude

The larger the amplitude, greater the energy of the 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 wave per second = 1 Hz

If this set of transverse waves pass a point in one second, what is the frequency? 4 Hz

Frequency of transverse waves


Frequency of waves – activity



Sound travels as waves made up of 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!


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 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 .


Transverse or longitudinal waves?



These waves are travelling across the surface of a pond. The length of each wave is 0.25 m.

From this example, the connection between speed, frequency and wavelength is:

How is wave speed calculated?

speed = frequency x wavelength

0.5 m/s = 2 Hz x 0.25 m

This means that the waves travel 0.5 m each second, so the speed of the waves is 0.5 m/s.

Two waves pass the duck each second, so the frequency is 2 Hz.


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 x wavelength

v = f x


x

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 =v


These waves are rippling across a pond.

The frequency of the waves is 0.2 Hz and the length of each wave is estimated at 0.15 m.

What is the wave speed?

Calculating wave speed – example

wave speed = frequency x wavelength

= 0.2 Hz x 0.15 m

= 0.03 m/s


Wave speed problems



amplitude – The maximum distance any point in a wave moves from its rest position.

compression – A stretched-out section of a longitudinal wave.

frequency – The number of waves passing a point each second. It is measured in hertz (Hz).

longitudinal wave – A type of wave in which the particles vibrate back and forth, which is parallel to the wave direction, e.g. sound and P waves.

rarefaction – A bunched-up section of a longitudinal wave. transverse wave – A type of wave in which the particles

vibrate up and down, which is at right angles to the wave direction, e.g. electromagnetic, water and S waves.

wavelength – The distance between two matching pointson neighbouring waves.

Glossary


Anagrams


Multiple-choice quiz

9. Wave Properties v2.0

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