Waves
What are waves?
• There are many different kinds
of wave:
• Light waves
• Sound waves
• Waves on water
• Seismic waves
• Waves along a rope, or a slinky
There are two sorts of waves
• Transverse waves
• Longitudinal waves
Transverse waves
• Most waves are transverse
• The vibrations in transverse waves go from side to side
• The energy is travelling in one direction, with the
vibrations moving at a 90o angle to the direction the
wave is travelling
Longitudinal waves
• Longitudinal waves have vibrations moving in the same
direction that the wave is travelling in
• Examples of longitudinal waves are:
Sound waves (in solids, liquids and gases)
Shock waves (e.g. seismic waves )
A slinky (when plucked)
Examples of different waves
Transverse waves:
Longitudinal waves:
• All electromagnetic
radiation, e.g. light
• Ripples on water
• Waves on strings
• A slinky that is
waved up and down
• Sound
• Shock waves
• A slinky when
plucked
What do waves do?
All waves
carry energy
What sort of energy is being carried?
• Heat energy is carried by light, infra red and
microwaves
• X-rays and gamma rays carry energy which
can cause ionisation and can damage cells
• Sounds carry energy in the form of vibrations.
Loud sounds can make an object vibrate
(move)
• Waves on water can move things, and can even
be used to generate electrical energy
• Televisions, radios, fibre optics and speech are
all ways in which energy travels (and also
information)
What does a wave look
like?
A wave can be drawn as a wavy line:
What are the main parts of a
wave?
• Wavelength
()
• This is the distance from the
crest of one wave to the
crest of the next wave
• Amplitude
• This is the height of a wave
from the mid-point (where
there is no displacement) to
a peak
• Frequency
(f)
• This is the number of
complete waves per second,
passing a certain point. It is
measured in Hertz (Hz)
Sound waves
• Sounds are produced by
vibrations
• Sound travels as longitudinal
pressure waves
• The frequency of a sound will
determine its pitch (how high or
low a sound is)
Hearing range
• Sounds can range from very
low frequencies (with a low
pitch) to very high frequencies
• Humans can only hear a
certain range of frequencies
(our hearing range)
• As we get older our hearing
range is reduced, and we do
not hear some of the higher
frequency sounds anymore
High frequency sounds
• High frequency
sounds have a high
pitch, like a mouse
squeaking
• High frequency
sounds have short
wavelengths
Ultrasound
• Bats send out very highpitched squeaks
• This is ultrasound
• Ultrasound will reflect off
objects in its path
• Bats can detect this and use
the information to know if
something is in their way,
and to fly around it (or to
catch it if it’s a moth)
How can we use ultrasound?
• Hospitals use ultrasound
scans to examine unborn
babies in the womb
• As the ultrasound waves
hit the foetus, some is
reflected, and a computer
converts this into an image
• Ultrasound waves are
safer than X-rays, which
can harm a foetus
Another use for ultrasound
waves:
• Sonar uses high frequency
sound waves which reflect
off the sea bed, or off
shoals of fish
• Reflected sound waves
coming back are detected
• Information obtained in
this way can tell us about
the features of the sea-bed,
the depth of the water, or
whether there is a shoal of
fish nearby.
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