03/08/2026
Waves
2016 EdExcel GCSE Physics
Topic 4
W Richards
Education Using
PowerPoint
What is a wave?
03/08/2026
A wave is a “movement of energy”. Notice that the “stuff” the
wave moves through doesn’t actually move from left to right,
but energy does!
Some definitions…
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1) Amplitude – this is
“how high” the wave is:
2) Wavelength () – this is the
distance between two
corresponding points on the
wave and is measured in metres:
3) Frequency – this is how many waves pass by every second
and is measured in Hertz (Hz).
By definition, frequency = 1/period (in s).
Transverse vs. longitudinal waves
Transverse
waves are when
the displacement
is at right angles
to the direction
of the wave…
Displacement
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Examples – light, water waves
Displacemen
t
Direction
Direction
Example – sound
Longitudinal
waves are when
the displacement
is parallel to the
direction of the
wave…
The Wave Equation
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The wave equation relates the speed of the wave to its
frequency and wavelength:
Wave speed (v) = frequency (f) x wavelength ()
in m/s
in Hz
in m
You need to learn
this equation!
V
f

Some example wave equation questions
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1) A water wave has a frequency of 2Hz and a wavelength
of 0.3m. How fast is it moving?
0.6ms-1
2) A water wave travels through a pond with a speed of
1ms-1 and a frequency of 5Hz. What is the wavelength
of the waves?
0.2m
3) The speed of sound is 330ms-1 (in air). When Dave
hears this sound his ear vibrates 660 times a second.
What was the wavelength of the sound?
0.5m
4) Purple light has a wavelength of around 6x10-7m and a
frequency of 5x1014Hz. What is the speed of purple
light?
3x108ms-1
Another wave equation
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Here’s another equation we can use for waves:
Wave speed (v) = distance (x) / time (t)
in m/s
in m
You need to learn
this equation!
x
v
in s
t
Some example wave equation questions
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1) A sound wave covers 600m in 2 seconds. What is its
speed?
300m/s
2) A wave travels at a speed of 2m/s. How far will it
travel in 20s?
40m
3) How long does light take to reach us from the sun if the
sun is 150 million km away and light travels at 3x108m/s?
500s
Measuring the speed of waves
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Task:
Design and carry out two experiments that will help you to
determine:
1) The speed of a ripple in water
2) The speed of sound in air
Water Waves (HT only)
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Q. How does wave speed depend on depth?
Design an experiment that explores the relationship between
the depth of water and the speed of a wave in that water.
Wavefronts
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A “wavefront” is basically the “crest” of a wave when viewed
from above:
Wavefronts
What happens when a wave hits03/08/2026
a
boundary? (HT only)
When a wave hits a boundary a number of things could happen:
1) It could be reflected
2) It could be transmitted
or refracted through the
material
3) It could be absorbed
Note that the frequency of the waves doesn’t change.
However, the velocity and wavelength might!
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Using Wavefronts to show Refraction
(HT only)
Let’s use wavefronts and the wave equation to show what
happens when an electromagnetic wave is refracted:
V
f

When this wave if refracted
it changes direction and
slows down. However, the
frequency does not change
to what happens to the
wavelength?
Sound Waves (Physics HT only)
03/08/2026
As we know, sound waves are formed when something vibrates.
But how does the sound reach our ears?
Air molecules
1) An object
makes a
sound by
vibrating
2) The vibrations
pass through air by
making air
molecules vibrate
3) These vibrations
are picked up by the
ear drum and other
parts of the ear,
which also vibrate
Converting Sound to Vibrations
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The ear
drum
The ear bones
In a microphone the sound waves
cause a diaphragm to move
Note that our ear drum and bones can only vibrate at a certain
rate. Therefore our hearing is limited to between 20Hz and
20,000Hz. This is called our “range of hearing”.
Infrasound
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Infrasound is the region of sound BELOW 20Hz (as opposed to
ULTRASOUND which is above 20KHz) – it can’t be heard by
humans. Some uses:
1) Communication between animals
African elephants use infrasound to
communicate with other elephants many
kilometres away.
2) Detecting movement in remote areas
3) Detecting volcanic eruptions and
meteors
Using Waves for Exploration
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Example 1 – Echo sounding
In echo-sounding, high frequency sound waves are reflected
from an object to measure the distance to that object:
Example 2 - Ultrasound
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Ultrasound is the region of sound above 20,000Hz – it can’t
be heard by humans. It can be used in pre-natal scanning:
How does it work?
Ultrasonic waves are partly _________ at the boundary as they pass from
one _______ to another. The time taken for these reflections can be
used to measure the _______ of the reflecting surface and this
information is used to build up a __________ of the object.
Words – depth, reflected, picture, medium
Example 3 - Earthquakes
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Here’s the structure of the Earth:
A thin crust 10-100km thick
A mantle – has the
properties of a solid
but it can also flow
A core – made of
molten nickel and iron.
Outer part is liquid
and inner part is solid
How do we know this? These facts have all been
discovered by examining seismic waves (earthquakes)