This document covers key concepts in physics related to waves, including types of waves (transverse and longitudinal), their properties (amplitude, wavelength, frequency, speed), and phenomena such as reflection, refraction, and diffraction. It details the electromagnetic spectrum and the use of waves for communication and sound. Examples of mechanical and electromagnetic waves, as well as the behavior of sound waves, are explained alongside their applications in real-world scenarios.

1. Unit 1 - Chapter 5
AQA GCSE PHYSICS
Waves

2. Keywords of this chapter
● Transverse wave - Wave in which the vibrations are perpendicular to the
direction of energy transfer.
● Oscillation - Moving to and fro about a certain position along a line.
● Perpendicular - At right angles.
● Longitudinal wave - Wave in which the vibrations are parallel to the direction of
energy transfer.
● Compression - Squeezed together.
● Rarefaction - Stretched apart.
● Electromagnetic wave - Electric and magnetic waves disturbance that transfers
energy from one place to another. The spectrum of electromagnetic waves, in
order of increasing wavelength, is as follows: gamma and X-rays, ultraviolet
radiation, microwaves, radio waves.
● Mechanical wave - Vibration that travels through a substance.

3. More keywords...
● Amplitude - The height of a wave crest or a wave trough of a transverse wave
from the rest position.
● Wavelength - The distance from one wave crest to the next wave crest (along
the waves).
● Frequency - The number of wave crests passing a fixed point every second.
● Speed - Distance moved / time taken
● Plane mirror - A flat mirror.
● Normal - Straight line through the surface or boundary perpendicular to the
surface or boundary
● Angle of incidence - Angle between the incident ray and the normal.
● Angle of reflection - Angle between the reflected ray and the normal.
● Real image - An image formed where light rays meet.

4. A few more words...
● Virtual image - An image, seen in a lens or a mirror, from which light rays
appear to come after being refracted by the lens or reflected by the mirror.
● Boundary - Line along which two substances meet.
● Refraction - The change of direction of a light ray when it passes across a
boundary between two transparent substances (including air).
● Diffraction - The spreading of waves when they pass through a gap or around
the edges of an obstacle that has a similar size as the wavelength of the wave.
● Sound - A form of mechanical energy.
● Echo - Reflection of sound that can be heard.
● Pitch - The pitch of a sound increases if the frequency of the sound waves
increases.

5. The nature of waves
● Youtube videos: https://www.youtube.com/watch?v=egcB0NbKPQI
● https://www.youtube.com/watch?v=GNPlcoVXL7M
https://www.youtube.com/watch?v=9LkLj8TS9VI&feature=iv&src_vid=UR2rjO0TkU0&annotation_id=annotation_2659666575
● We use waves to transfer energy and transfer information.
● There are different types of waves including mechanical waves and electromagnetic waves.
● Electromagnetic waves can all travel through a vacuum at the same speed of 300 000 kilometres per second. The waves cover a
continuous range of wavelengths called the electromagnetic spectrum.
● Sound waves, water waves and seismic (produced by earthquakes) waves are all examples of mechanical waves. Meaning these
waves are vibrations which travel through a medium (substance) and cannot travel through a vacuum.
Google definition of waves:

6. Transverse waves
The vibrations of a transverse wave are perpendicular to
the direction in which the waves transfer energy.
The amplitude is the displacement
from the rest position to the crest.
The wavelength is the length of a
full cycle of the wave (from one
crest to the next).
Frequency is the number of
complete waves passing a certain
point per second or the number of
waves produced by a source each
second. Frequency is measured in
hertz (Hz). 1 Hz is 1 wave per
second.
Examples of transverse waves:
1. Light and all other EM waves
2. Ripple on water.
3. Waves on strings.
4. A slinky spring wiggled up and down.

7. Longitudinal wave
The vibrations of a longitudinal wave is parallel to the direction
in which the waves are travelling.
Examples of longitudinal waves:
1. Sound waves and ultrasound.
2. Shock waves, e.g. seismic waves.
3. A slinky spring when you push the end.
Vibrations in same direction as
wave is traveling
The wavelength of a
longitudinal wave is the
distance from the middle of
one compression to the
middle of the next
compression. This is the
same as the middle of one
rarefaction to the middle of
the next rarefaction.
The frequency of a
longitudinal wave is the
number of compressions
passing a point in one
second.

8. Equation for the speed of a wave
The speed of the wave is
usually independent of the
frequency or amplitude of
the wave.
All electromagnetic waves
travel at about the speed of
300 000 Km.
For waves of constant frequency, the speed of the
waves depends on the frequency and the wavelength
as follows:

9. Key points
● We use waves to transfer energy and transfer information.
● Transverse waves vibrate at right angles to the direction of energy transfer of the
waves. All electromagnetic waves are transverse waves.
● Longitudinal waves vibrate parallel to the direction of energy transfer of the waves.
A sound wave is an example of a longitudinal wave.
● Mechanical waves, which need a medium (substance) to travel through, may be
transverse or longitudinal waves.
● For any wave, its amplitude is the height of the wave crest or the depth of the wave
trough from the position at rest.
● For any wave, its frequency is the number of wave crests passing a point in one
second.
● For any wave, its wavelength is the distance from one wave crest to the next wave
crest. This is the same as the distance from one wave trough to the next wave
trough.
● V = f x λ

10. The electromagnetic spectrum
The electromagnetic spectrum extends from high frequency or high energy
(short wavelength 10^-15 m) waves, e.g. gamma rays, to low frequency or
low energy (long wavelengths 10^4m) waves, e.g. radio waves.
Visible light is one type of electromagnetic radiation and is the only part of the
electromagnetic spectrum that can be seen with the eye. It consists of seven
primary band of colour from red to violet.
Long wavelengths, low
frequency
Short wavelengths, high
frequency

11. Communication
● Different parts of the electromagnetic spectrum can be used for communication.
● Radio waves - used for television and radio signals allowing communication across the Earth.
● Microwaves - Used for mobile phone networks and satellite communication (although there are
potential risks of using mobile phones, e.g. possible links with brain tumourS) and can be used for
cooking - water molecules absorb microwaves and heat up.
● Infrared - Used for remote controls for televisions. Also used in grills, toasters and radiant heaters
(e.g. electric fires). Infrared is also used for optical fibre communication.
● Visible light is used for morse code with torches, photography and fibre optics.

12. Reflection 1
Youtube video: https://www.youtube.com/watch?v=iUguHQMf0i8
● All waves can be reflected.
● Reflection of light is what allows us to see objects. Light bounces off them into
our eyes.
● When light travelling in the same direction reflects from an uneven surface
such as a piece of paper, the light reflects off at different angles. However,
when a light travelling in the same direction reflects from an even surface
(smooth and shiny like a mirror) then it’s all reflected at the same angle and
you get a clear reflection.
● A plane (flat) mirror enables you to see an exact mirror image of yourself.
Google definition of
reflection.

13. Reflection 2
Angle of incidence = Angle of reflection
The normal is a line perpendicular to
the mirror at the point where the
incident ray hits the mirror.
The angle of incidence is the angle
between the incident ray and the
normal.
The angle of reflection is the angle
between the reflected ray and the
normal.

14. Image formation by a plane mirror
This ray diagram shows the path of two
light rays from an object that reflect off
the mirror. The image and the object
are at equal distances from the mirror.
The image formed by a plane mirror is virtual,
upright (the same way up as the object) and
laterally inverted (back to front but not upside
down). A virtual image can’t be projected on the
screen like the movie images that are seen in the
cinema. An image on a screen is described as a
real image because it is formed by focusing light
rays on the screen.
A real image is one that can be formed on a screen,
because the rays of light that produce the image
actually pass through it.
A virtual image cannot be formed on a screen,
because the rays of light that produce the image only
appear to pass through it.

15. Refraction ● Youtube:
https://www.youtube.com/watch?v=7aU8sX8cFNs,
https://www.youtube.com/watch?v=dwu3Bv9KARw,
https://www.youtube.com/watch?v=QoZA9EwUt-M
● Refraction is a property of all forms of waves
including light and sound.
● When a wave crosses a boundary between two
substances (e.g. from air to glass) it changes
direction.
● A light ray changes directions towards the normal
when it travels from air into glass. The angle of
refraction (r) is smaller than the angle of incidence (i).
This is because the light slows down.
● The light ray changes direction away from the normal
when it travels from glass to air. This is because the
light ray speeds up. The angle of refraction (r) is
greater than the angle of incidence.
● Wave change speed when they cross a boundary
between different substances. The wavelength of the
wave also changes, but the frequency stays the
same.
● The change in speed of the waves causes a change
in direction.
● If the wave is travelling along a normal, then it will not
change direction.
Glass block
Ray
box
Normal
i
r

16. Refraction by a prism
A narrow beam of white light passes through a
triangular glass prism where the beams comes out of
the prism in a different direction to the incident ray and
is split into the colours of the spectrum. This is called
dispersion.
White light contains all the colours of the spectrum.
Each colour of light is refracted slightly differently. So
the prism splits the light into colours.
Violet light is refracted the most and red light is
refracted the least.

17. Diffraction
● Youtube: https://www.youtube.com/watch?v=UR2rjO0TkU0
https://www.youtube.com/watch?v=-QYQDJ7CSVQ,
https://www.youtube.com/watch?v=POMsF0Fd_SE
● Diffraction is a property of all waves, including light and sound.
● Diffraction is the spreading of waves when they pass through an obstacle.
This effect is more noticeable if the wavelength of the waves is about the
same size as the gap or obstacle.
● Light is really hard to diffract due its really small wavelength.

18. The narrower the gap, the more waves spread out. The
wider the gap, the less waves spread out.
Diffraction of ultrasonic waves is an important factor in
the design of an ultrasonic scanner. Ultrasonic waves
are sound waves at frequencies above the range of the
human ear. An ultrasonic scan can be made of a baby in
the womb.
TV signals are carried by radio waves. People living in
hilly areas may not be able to receive a signal because
it is blocked by a hill. Radio waves passing he hill will be
diffracted round the hill. If they do not diffract enough,
the radio and TV signals will be poor.
The ultrasonic waves spread out
from a hand-held transmitter and
then reflect from the tissue
boundaries inside the womb. If
the transmitter is too narrow, the
waves spread out too much and
image is not very clear.

19. Sound
● Youtube: https://www.youtube.com/watch?v=Fsob8X15S2Y , https://www.youtube.com/watch?v=PCN4RIQIVTo
● Sound waves are longitudinal waves because the air particles vibrate along the direction in which the waves transfer energy
and cause vibrations in a medium, which are detected as sound. Also sound waves cannot travel through a vacuum
● Any objects vibrating in air makes the layers of air near the object vibrate making the further layers of air also vibrate. This
sends out the vibrations of the sir in waves of compressions and rarefactions. When the waves reach your ears, they make
your eardrums vibrate in and out so you hear sound as a result.
● A machine called an oscilloscope converts longitudinal waves into a transverse wave making it easier to analyse.
● Echoes are reflections of sounds - can be heard in places with bare, flat and smooth surfaces. If the walls are covered in
fabric, the fabric will absorb sound instead of reflecting it, meaning no echoes will be heard. Also if the wall surface is uneven
(not smooth), echoes will not be heard because the reflected sound is scattered and broken up. Soft tings absorb sound well.
● Sound waves travel through air at a frequency of about 340 m/s. The warmer the air, the greater the speed of sound.
Refraction takes place at the boundaries between layers of air at different temperature. In the daytime, sound refracts
upwards, not downwards(like at night), because the air near the ground is warmer than the air higher up.
● The pitch of a sound is determined by its frequency (as the frequency increases the pitch becomes higher) and loudness by
its amplitude(higher the amplitude, the louder the sound).
● The human ear can hear frequencies of sound in the range between 20 Hz and 20 000 Hz (20kHz). The ability to hear higher
frequencies declines with age.
● Sound waves generally travel fastest through solids and slowest through gases.

20. The higher the frequency of the sound waves, the higher the
pitch of the sound. The higher the amplitude, the louder the
sound. Differences of waveform can be show in an
oscilloscope similar to the one to the left.
Turning fork and signal generators produce ‘pure’
waveforms. The quality of a note depends on the
waveform. Musical instruments sound so different
from each other because each instrument make
different waveforms. Vibrations created in an
instrument when it is played produce sound
waves.
In some instruments, a saxophone has a column
of air which vibrates. In a violin the strings
vibrates An xylophone vibrate when they are
struck.
The instrument resonates at these certain
frequencies when a new cycle of vibrations
makes a vibration stronger at certain frequencies.

21. Key points
● The normal at a point on a mirror is a line drawn perpendicular to the mirror.
● For a light ray reflected by a plane mirror: The angle of incidence is the angle between the incident ray
and the normal and the angle of reflection is the angle between the reflected ray and the normal.
● The law of reflection states that: the angle of incidence = the angle of reflection.
● Refraction is the change of direction of waves when they travel across a boundary.
● When a light ray refracts as it travels from air to glass, the angle of refraction is less than the angle of
incidence. However, when a light ray refracts as it travels from glass into the air, the angle of refraction is
greater than the angle of incidence.
● Diffraction is the spreading out of waves when they pass through a gap or round the edge of an obstacle.
● The narrower a gap is, the greater the diffraction is.
● If radio waves do not diffract enough when they go over hills, radio and TV reception will be poor.
● The frequency range of the normal human ear is from about 20 Hz to about 20 000 Hz.
● Sound waves are vibrations that travel through a medium (substance). They cannot travel through a
vacuum (as in space).
● Echoes are due to sound waves reflected from a smooth, hard surface.
● The pitch of a note increases if the frequency of the sound wave increases. Similarly, the loudness of a
note increases if the amplitude of the sound waves increases.
● Vibrations created in an instrument when it is played produce sound waves.