Physics Unit 6: Waves
GCSE Revision Notes
Waves transfer energy in the direction they are travelling.
When waves travel through a medium, the particles of the medium oscillate and transfer
energy between each other. But overall, the particles stay in the same place – only energy is
transferred.
Amplitude: The maximum displacement of a
point on the wave from its undisturbed
position.
Wavelength: The distance between the same
point on two adjacent waves.
Frequency: The number of complete waves
passing a certain point per second, measured
in hertz (Hz).
Period: The amount of time it takes for a full
cycle of the wave, measured in seconds (s).
Wave fronts are a useful way of picturing waves from above: Each wave front is used to
represent a single wave (we just show the peaks of waves as lines).
Period (s) = 1 ÷ Frequency (Hz)
T=1÷f
Transverse waves:
In transverse waves, the oscillations are
perpendicular (at 90°) to the direction of energy
transfer.
Examples: All electromagnetic waves, ripples and
waves in water, a wave on a string.
Longitudinal waves:
In longitudinal waves, the oscillations
are parallel to the direction of energy
transfer.
Examples: Sound waves in air, ultrasound,
shock waves.
Wave speed (m/s) = Frequency (Hz) x Wavelength (m)
v=fxλ
Wave speed: The speed at which energy is being transferred, this applies to all waves.
Measuring wave speed:
Ripples on a water surface – this method can also be performed using a ripple tank
1
, 1. One method for measuring the speed of a ripple on a water surface is to use a large calm
pond or lake.
2. Two people stand a few metres apart (measured using a tape measure).
3. One person counts down from three and then disturbs the water surface (using their hand,
for example) to create a ripple.
4. The second person uses a stopwatch to time how long it takes for the ripple to get to them
from the first person.
5. The experiment is then repeated several times and an average time calculated.
6. The speed of the wave can then be found using the equation: wave speed = frequency x
wavelength.
Measuring the speed of sound
1. Two people stand a distance of around 100m apart.
2. The distance between them is measured using a trundle wheel.
3. One of the people has two wooden blocks, which he bangs together above his head.
4. The second person has a stopwatch which he starts when he sees the first person banging
the blocks together and stops when he hears the sound.
5. This is then repeated several times and an average value is taken for the time.
6. The speed of sound can then be calculated using the equation: speed = distance ÷ time.
Measuring the speed of sound using an oscilloscope
1. Two microphones are connected to an oscilloscope and placed about 5 m apart.
2. (This distance can be measured using a tape measure).
3. The oscilloscope is set up so that it triggers when the first microphone detects a sound, and
the time base is adjusted so that the sound arriving at both microphones can be seen on the
screen.
4. Two wooden blocks are used to make a large clap next to the first microphone.
5. The oscilloscope is then used to determine the times at which the clap reaches each
microphone, and the time difference between the two claps is then determined.
6. This is repeated several times and an average time difference calculated.
7. The speed can then be calculated using the equation: speed = distance ÷ time.
Waves at a boundary:
When waves arrive at a boundary between two different materials, three things can happen:
1. The waves are absorbed by the material the wave is trying to cross into
2. The waves are transmitted – the waves carry o travelling through the new material.
3. The waves are reflected.
What happens depends on the wavelength of the wave and the properties of the materials
involved.
Reflection:
Angle of incidence = angle of reflection.
The angle of incidence is the angle
between the incoming wave and the
normal (line at 90° to the boundary).
2
GCSE Revision Notes
Waves transfer energy in the direction they are travelling.
When waves travel through a medium, the particles of the medium oscillate and transfer
energy between each other. But overall, the particles stay in the same place – only energy is
transferred.
Amplitude: The maximum displacement of a
point on the wave from its undisturbed
position.
Wavelength: The distance between the same
point on two adjacent waves.
Frequency: The number of complete waves
passing a certain point per second, measured
in hertz (Hz).
Period: The amount of time it takes for a full
cycle of the wave, measured in seconds (s).
Wave fronts are a useful way of picturing waves from above: Each wave front is used to
represent a single wave (we just show the peaks of waves as lines).
Period (s) = 1 ÷ Frequency (Hz)
T=1÷f
Transverse waves:
In transverse waves, the oscillations are
perpendicular (at 90°) to the direction of energy
transfer.
Examples: All electromagnetic waves, ripples and
waves in water, a wave on a string.
Longitudinal waves:
In longitudinal waves, the oscillations
are parallel to the direction of energy
transfer.
Examples: Sound waves in air, ultrasound,
shock waves.
Wave speed (m/s) = Frequency (Hz) x Wavelength (m)
v=fxλ
Wave speed: The speed at which energy is being transferred, this applies to all waves.
Measuring wave speed:
Ripples on a water surface – this method can also be performed using a ripple tank
1
, 1. One method for measuring the speed of a ripple on a water surface is to use a large calm
pond or lake.
2. Two people stand a few metres apart (measured using a tape measure).
3. One person counts down from three and then disturbs the water surface (using their hand,
for example) to create a ripple.
4. The second person uses a stopwatch to time how long it takes for the ripple to get to them
from the first person.
5. The experiment is then repeated several times and an average time calculated.
6. The speed of the wave can then be found using the equation: wave speed = frequency x
wavelength.
Measuring the speed of sound
1. Two people stand a distance of around 100m apart.
2. The distance between them is measured using a trundle wheel.
3. One of the people has two wooden blocks, which he bangs together above his head.
4. The second person has a stopwatch which he starts when he sees the first person banging
the blocks together and stops when he hears the sound.
5. This is then repeated several times and an average value is taken for the time.
6. The speed of sound can then be calculated using the equation: speed = distance ÷ time.
Measuring the speed of sound using an oscilloscope
1. Two microphones are connected to an oscilloscope and placed about 5 m apart.
2. (This distance can be measured using a tape measure).
3. The oscilloscope is set up so that it triggers when the first microphone detects a sound, and
the time base is adjusted so that the sound arriving at both microphones can be seen on the
screen.
4. Two wooden blocks are used to make a large clap next to the first microphone.
5. The oscilloscope is then used to determine the times at which the clap reaches each
microphone, and the time difference between the two claps is then determined.
6. This is repeated several times and an average time difference calculated.
7. The speed can then be calculated using the equation: speed = distance ÷ time.
Waves at a boundary:
When waves arrive at a boundary between two different materials, three things can happen:
1. The waves are absorbed by the material the wave is trying to cross into
2. The waves are transmitted – the waves carry o travelling through the new material.
3. The waves are reflected.
What happens depends on the wavelength of the wave and the properties of the materials
involved.
Reflection:
Angle of incidence = angle of reflection.
The angle of incidence is the angle
between the incoming wave and the
normal (line at 90° to the boundary).
2
