AQA GCSE Combined Science Waves Knowledge Organiser

Transverse and Longitudinal Waves Wave Properties Required Practical: Observing Waves
Waves can be either transverse or longitudinal. Make observations to identify the suitability of apparatus to measure the
frequency, wavelength and speed of waves.
In a transverse wave, the vibrations of the particles are peak
lamp
perpendicular (at right angles) to the direction of energy
transfer. The wave has peaks (or crests) and troughs. Waves in a Ripple Tank
Examples of transverse waves include water waves and The diagram shows the apparatus most power
wavelength
electromagnetic waves. commonly used for this investigation. supply

vibration
Method: dipper
amplitude motor
1. Set up the apparatus as shown in water
undisturbed
the diagram.
position
energy amplitude 2. Turn on the power supply and
transfer observe the waves produced in
the water. Make any necessary
wavelength adjustments to the equipment,
for example altering the potential white
In a longitudinal wave, the vibrations of the particles are trough difference of the power supply, so paper
parallel to (in the same direction as) the direction of energy that the waves are clear to observe.
transfer. A longitudinal wave has areas of compression and The lower the frequency of the waves, the easier it will be for
rarefaction. Sound waves travelling through air are an measurements to be made.
example of this type of wave. The amplitude of a wave is the distance from the undisturbed position to the
peak or trough of the wave. 3. To measure the wavelength, use a metre ruler to measure the length of
10 waves and divide this value by 10 to find one wavelength. Repeat this
vibration The wavelength is the distance from a point on one wave to the same point several times and calculate the mean wavelength. A stroboscope can be
on the next wave, measured in metres (m).
used to freeze the wave pattern to make it easier to measure the waves.
The frequency of a wave is the number of waves that pass a given point every
4. To measure the frequency, mark a point on the white paper and count
second, measured in hertz (Hz).
the number of waves that pass this point in 10 seconds. Divide the number
The period of a wave is the time taken for a full wave to pass a given point, of waves by 10 to find the number of waves that pass per second. Repeat
measured in seconds (s). this several times and calculate the mean frequency.
5. To calculate wave speed, use the equation:

When a wave travels through a medium, energy is transferred 1 1 wave speed = frequency × wavelength
period = or T =
by the particles but the matter itself does not move. frequency f pulley
string
Waves in a Solid power
This can be shown by supply
placing a cork in a tank Wave speed is how quickly energy is transferred through a medium (or how Waves in a solid can
be observed using signal generator masses
of water and generating quickly the wave travels), measured in metres per second (m/s). (to create tension)
ripples across the surface. the apparatus shown
in the diagram. metre ruler
The cork will move up and
down on the oscillations wave speed = frequency × wavelength or v = f λ
When the signal
of the wave, but it will not generator is switched
travel across the tank. The speed of a sound wave travelling through the air can be measured using on, the string begins
a simple method. A person stands a measured distance from a large flat wall, to vibrate.
e.g. 100m. The person then claps their hands and the time taken to hear the
Similarly, when sound waves move from a speaker towards the echo is measured. The speed of sound can be calculated using the equation: The frequency of the signal generator, the length of the string or the tension in
ear, the air particles next to the speaker do not move towards the string is adjusted until a clear wave pattern can be seen. The wave should
the ear; they vibrate around their original position. not look like it is moving.
distance To find the wavelength, count the number of half wavelengths (single loops) in
speed = 1 metre, then divide the length by the number of half wavelengths and multiply
time
by two.
The frequency of the wave is the frequency of the signal generator.
Remember, the distance that the sound wave has travelled will be double the
distance between the person and the wall because the wave has travelled to Wave speed can be calculated using the equation:
the wall and back again. It is important to take several measurements and
calculate the mean to reduce the effect of human error in your measurements. wave speed = frequency × wavelength

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 AQA GCSE Combined Science Waves Knowledge Organiser
The Electromagnetic Spectrum Properties of Electromagnetic Waves
Electromagnetic waves are transverse waves. They transfer energy from a source to an absorber. All When a wave moves into a medium with a different density (e.g. from air into glass), the wave changes direction.
electromagnetic waves travel at the same speed through a vacuum or air. They are grouped by their wavelength This is called refraction. This can be represented by a ray diagram.
and frequency to form a continuous spectrum.
When a wave enters the glass block at an angle to the
decreasing frequency normal, it bends towards the normal. The angle of refraction
is smaller than the angle of incidence. The angle at which

normal
1m – 103m 10-2m 10-4m 10-6m 10-8m 10-10m 10-12m B
the wave leaves the glass block (angle of emergence) is
equal to the angle at which it enters the glass block (angle
of incidence).
If a wave enters a different medium at 90° (perpendicular) to
the boundary, it will not change direction but instead carry
r r
increasing frequency on in a straight line.
(HT only) Refraction occurs due to the difference in density glass
of the two materials. When a wave moves from a less dense air
medium to a more dense medium (e.g. from a gas to a
solid), it slows down and bends towards the normal. When B

normal
radio waves microwaves infrared Visible light ultraviolet X-rays gamma rays a wave moves from a more dense medium to a less dense A = angle of incidence
medium (e.g. from a solid to a gas), it speeds up and bends B = angle of emergence
Remember: Roman Men Invented Very Unusual X-ray Guns away from the normal. r = angle of refraction

Electromagnetic Hazards and Risks of

Wave Uses and Applications Explanation (HT only) Extra Information
Electromagnetic Waves
(HT Only) Oscillations in electrical circuits can
produce radio waves. Ultraviolet waves, X-rays and gamma
terrestrial television and radio Radio waves can be transmitted over long distances by reflecting them rays have some risks associated with
radio waves communications off a layer of the Earth’s atmosphere called the ionosphere. them.
(HT Only) An alternating current can be produced
when radio waves are absorbed.
How dangerous electromagnetic
radiation is depends on the type of
Microwaves can penetrate the Earth’s atmosphere to communicate with
satellite communication, satellite satellites. When water molecules absorb microwaves, it causes their Microwaves are used in mobile phone wave and the dosage.
microwaves television, heating food communications as well as satellite television.
internal energy store, and therefore their temperature, to increase.
Radiation dosage is measured in
sieverts (Sv) or millisieverts (mSv).
cooking, thermal imaging camera,
electric heaters, short-range Infrared waves cause heating as they are absorbed by matter. Infrared
infrared cameras can detect infrared radiation to produce thermal images. Infrared radiation can cause burns to skin.
communications (remote controls) Safe limits of exposure of each type
of radiation are known and can be
referred to when assessing the risk of
In fibre-optic cables, pulses of visible light are used to send coded using electromagnetic radiation.
visible light vision, fibre optic communication signals over large distances. The human eye can only detect visible light waves.

energy efficient lamps, sun tanning, Absorption of ultraviolet waves by the skin can
detecting forged bank notes, Some chemicals absorb energy from ultraviolet waves and then emit increase the risk of skin cancer and lead to
ultraviolet this energy as visible light. This is known as fluorescence.
sterilising water premature ageing of the skin.

X-rays can penetrate soft tissue, such as muscles and skin, but are X-ray absorption by human tissues can lead to gene
X-rays medical imaging, airport security absorbed by hard structures like bones. mutation and cancer.

sterilising medical equipment, Gamma rays are highly penetrating and can easily pass through Gamma rays are produced by changes in the nucleus
gamma rays sterilising food, radiotherapy for body tissues. The ionising ability of gamma rays means that they can of an atom. Gamma ray absorption by human tissues
cancer treatment damage cancerous cells (as well as healthy ones). can lead to gene mutation and cancer.

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 AQA GCSE Combined Science Waves Knowledge Organiser
Properties of Electromagnetic Waves Required Practical: Radiation and Absorption
(HT Only) Different substances absorb, reflect, refract or transmit electromagnetic waves in different ways. Investigate how the nature of a surface affects the amount of infrared radiation absorbed or radiated by that
This may change depending on the wavelength of the electromagnetic wave. surface.
A wave front diagram shows that as a wave moves from a less dense to a more dense medium (e.g. from air into In this investigation, you are finding out which type of surface emits the most infrared radiation:
water), at an angle to the normal, it slows down and its wavelength decreases. One side of the wave • dark and matt
reaches the more dense medium first, causing the wave to change direction. Although the wavelength decreases,
• dark and shiny Leslie cube
the frequency of the wave remains the same due to its change in speed. infrared detector
• light and matt
When a wave moves from a more dense medium into a less dense medium, the reverse happens. The • light and shiny
wave speeds up and its wavelength increases. The frequency of the wave remains the same.

Method:
1. Place the Leslie cube on a heatproof mat.
2. Boil some water in a kettle, fill the Leslie cube
with hot water and put the lid on.

water
3. Use a thermometer or an infrared detector to
air measure the amount of infrared radiation
water air emitted from one of the surfaces of the Leslie
cube. heatproof mat

4. Repeat the experiment for each surface of the

Leslie cube, ensuring that the infrared detector
is an equal distance from each surface.

You should find that a dark, matt surface emits much more infrared radiation than a light, shiny surface.

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