Transverse and Longitudinal
All waves are either transverse or longitudinal.
All waves transfer energy from one place to another. Ripples transfer kinetic energy. Sound waves
transfer sound energy.
Draw diagram.
Oscillations are the movements where the wave is moving up and down.
In transverse waves e.g., ripples on the surface of water, the oscillations are perpendicular to the
direction of energy transfer. In transverse waves, the oscillations are up and down but the direction
of energy is sideways. Not all transverse waves require a medium.
Compressions are regions where the air particles are close together.
In between compressions are rarefactions where the air particles are spaced out.
In longitudinal waves e.g., sound waves traveling in air, the oscillations are parallel to the direction
of energy transfer. All longitudinal waves require a medium to travel in e.g., air, a liquid or a solid.
It is the wave that travels not the medium.
Properties of Waves
Draw diagrams.
The amplitude of a wave is the maximum displacement of a point on a wave away from its
undisturbed position.
The wavelength of a wave is the distance from a point on one wave to the equivalent point on the
adjacent wave. The symbol for wavelength is the Greek letter lambda (λ). The wavelength on a
longitudinal wave is the distance from one compression to the next compression or rarefaction to
the next rarefaction.
The frequency of a wave is the number of waves passing a point each second. The unit is Hertz (Hz).
1 Hz = 1 wave per second.
The period is the time (in seconds) for one wave to pass a point.
Period (s)= 1 / frequency (Hz) T = 1 / f
Question: A wave has a frequency of 100 Hz. Calculate the period of the wave.
Answer: T =
T = 0.01 sec
The Wave Equation
The wave speed is the speed at which the energy is transferred (or the waves moves) through the
medium.
V=fxλ
Wave speed (m/s) = frequency x wavelength
,Question: A wave has a frequency of 165 Hz and a wavelength of 2 m. Calculate the speed of the
wave.
Answer: v = 165 x 2
V = 330 m/s
Question: A wave has a frequency of 10 000 Hz and a wavelength of 2 cm. Calculate the speed of the
wave.
Answer: 2 cm = 0.02 m
V = 10 000 x 0.02
V = 200 m/s
Question: A wave has a speed of 500 m/s and a frequency of 200 Hz. Calculate the wavelength.
Answer: λ = v / f
λ =
Λ = 2.5 m
Draw diagram.
Method to measure the speed of sound waves in the air:
Separated by a distance of 500 m, Person a is holding a pair of cymbals and Person B is a timer.
Person B starts timing when she sees Person A clash the cymbals together. Person B then stops the
timing when she hears the sound of the cymbals clashing. The speed of the sound waves then can be
calculated by dividing the distance travelled by the time taken.
Problems with the experiment: every person has a different reaction time. It takes a fraction of a
second between seeing the cymbals and starting the timer as well as hearing the sound and stopping
the timer. This error can be reduced by having a large number of observers with timers. We take all
their results and discard any anomalies and then calculate a mean value. The time between seeing
the cymbals clash and hearing the sound is very short making it difficult to press the time at the
correct times. This can be reduced by increasing the distance between the two people. The longer
the distance the longer the time. That makes it easier to start and stop the time at the correct times.
Required Practical: Ripple Tank
Draw diagram.
A ripple tank is used to observe the features of water waves. A ripple tank is a shallow tray of water.
In the water is a vibrating bar. The bar is connected to a power pack. When the bar vibrates, it
creates waves across the surface of the water. Above the ripple tank is the lamp and below the tank
is a sheet of white paper. When light shines through the water, it produces an image of waves on the
paper. We use this set up to measure the wavelength, frequency and speed of the water waves. Th
easiest way to do this is to record the waves using a mobile phone, it allows us to play back the
recording at different speeds or to freeze the image completely.
,To measure the wavelength, place a ruler on the paper. Then freeze the image of the waves. Now
measure the distance between one wave and 10 waves further (total of 10 wavelengths). To one
wavelength, divide this by ten.
To find the frequency, place a timer next to the paper and count the number of waves passing a
point in a second. It is more accurate to count the number of waves in 10 seconds and then divide by
10. This is easier if recorded and then watched in slow motion. Remember to record the time as well
as the waves.
We already know the wavelength and the frequency of the waves; we can use the wave equation to
determine the speed. Another way to determine the wave speed is to select a wave and measure
the time it takes to move the length of the tank. Calculate the speed by dividing the distance
travelled by the time taken. Might get slightly different results using these two methods because of
measurement errors e.g., timing.
Required Practical: Waves in a Solid
Draw diagram.
String with one end attached to a vibration generator. At the other end of the string is a hanging
mass which keeps the string taut. The vibration generator is attached to a signal generator (which
allows us to change the frequency of vibration of the string). When the power is turned on, the
string vibrates. At a certain frequency, we get a standing wave. This is due to an effect called
resonance. Standing waves are found in stringed musical instruments such as a guitar. The
wavelength of the standing wave is measured using a ruler. We need to measure the total length of
the standing wave from the wooden bridge to the vibration generator. This can be used to calculate
the speed of the wave using the wave equation. The frequency is read from the signal generator.
Draw diagram.
If the frequency is increased, at a certain frequency the standing waves change to 3 half
wavelengths. To calculate the wavelength of this, we need to divide the total length by the number
of half wavelengths and then multiply by 2.
The wave speed of the string does not depend on the frequency or the wavelength. The wave speed
depends on the taughtness of the string and the mass / cm.
Reflection of Waves
Draw all diagrams.
When a wave hits a boundary with a different material e.g., glass, the wave could simply be
transmitted through the material, the energy of the wave could be absorbed by the material (if that
happens, then the wave may not pass through the material at all) or the wave may simply be
reflected off the surface of the material. The surface of a material can transmit, absorb or reflect a
wave. Which of these happens depends both on the material and the wavelength of the wave.
In certain case, waves can change direction when they pass from one material to another. This is
called refraction.
Light reflecting off the surface of a mirror.
Draw diagram.
, The incident ray is a ray of light striking the surface of the mirror. The arrow shows the direction of
the ray. Start by drawing the normal (a dotted line at right angles to the surface of the mirror). Then
measure the angle between the incident ray and the normal. This is called the angle of incidence.
Draw a reflected ray. The angle of reflection equals the angle of incidence.
Draw diagrams.
Required Practical: Reflection and Refraction
Equipment: ray, box, lens and slit. This produces a narrow ray of light. Ray boxes get hot so it’s
important to switch them off when they are not being used. This practical could also be done using a
laser but that can be more dangerous so a ray box is safe.
Draw diagrams.
First take a piece of A3 paper and draw a straight line down the centre using a ruler. Then use a
protractor to draw a line at right angles. This is the normal. Now place a glass block against the first
line so that the normal is near the centre. Now draw around the glass block. At this point, turn out
all the lights in the room. Next use the ray box to direct a ray of light so it hits the block at the
normal. This is the incident ray. The angle between the incident ray and the normal is the angle of
incidence. Now adjust the ray box to change the angle of incidence. At a certain angle, we can see a
ray reflect from the surface of the block. We can also see another ray leaving the block from the
opposite side. This is the transmitted ray. Now mark the path of the incident ray and reflected ray
with crosses and the transmitted ray.
Now turn on the room lights and switch off the ray box. Finally, remove the glass block. Now draw in
both the incident ray and the reflected ray. Next draw in the transmitted ray so it meets the position
of the block. Draw a line to show the path of the transmitted ray through the glass block. Now use a
protractor to measure the important angles. Both the angle of incidence and angle of reflection need
to be measured, then the angle of refraction (the angle between the normal and the path of the
transmitted ray through the block).
Now do the whole experiment again but use a block made from a different material e.g., a plastic
such as Perspex.
What you should find out is that the angles of incidence and reflection are the same for both glass
and Perspex because the angles of incidence and reflection do not depend on the material.
However, the angle of refraction will be different with Perspex than with glass because the angle of
refraction is different for different materials.
Sound Waves
Sound is a longitudinal wave. When sound waves move through air, the air particles vibrate from
side to side. These vibrations can pass from one medium to another e.g., air to a solid.
Sound waves can travel through solids causing vibrations in the solid. Sound waves can only move
through a medium e.g., air or solid as the waves move by particles vibrating. Sound waves cannot
pass through a vacuum as there are no particles. Just like light, sound waves can be reflected. A
reflected sound wave is called an echo.
Within the ear, sound waves cause the ear drum and other parts to vibrate which causes the
sensation of sound. The conversion of sound waves to vibrations of solids works over a limited
frequency range. This restricts the limits of human hearing. Partly because of that, normal human
All waves are either transverse or longitudinal.
All waves transfer energy from one place to another. Ripples transfer kinetic energy. Sound waves
transfer sound energy.
Draw diagram.
Oscillations are the movements where the wave is moving up and down.
In transverse waves e.g., ripples on the surface of water, the oscillations are perpendicular to the
direction of energy transfer. In transverse waves, the oscillations are up and down but the direction
of energy is sideways. Not all transverse waves require a medium.
Compressions are regions where the air particles are close together.
In between compressions are rarefactions where the air particles are spaced out.
In longitudinal waves e.g., sound waves traveling in air, the oscillations are parallel to the direction
of energy transfer. All longitudinal waves require a medium to travel in e.g., air, a liquid or a solid.
It is the wave that travels not the medium.
Properties of Waves
Draw diagrams.
The amplitude of a wave is the maximum displacement of a point on a wave away from its
undisturbed position.
The wavelength of a wave is the distance from a point on one wave to the equivalent point on the
adjacent wave. The symbol for wavelength is the Greek letter lambda (λ). The wavelength on a
longitudinal wave is the distance from one compression to the next compression or rarefaction to
the next rarefaction.
The frequency of a wave is the number of waves passing a point each second. The unit is Hertz (Hz).
1 Hz = 1 wave per second.
The period is the time (in seconds) for one wave to pass a point.
Period (s)= 1 / frequency (Hz) T = 1 / f
Question: A wave has a frequency of 100 Hz. Calculate the period of the wave.
Answer: T =
T = 0.01 sec
The Wave Equation
The wave speed is the speed at which the energy is transferred (or the waves moves) through the
medium.
V=fxλ
Wave speed (m/s) = frequency x wavelength
,Question: A wave has a frequency of 165 Hz and a wavelength of 2 m. Calculate the speed of the
wave.
Answer: v = 165 x 2
V = 330 m/s
Question: A wave has a frequency of 10 000 Hz and a wavelength of 2 cm. Calculate the speed of the
wave.
Answer: 2 cm = 0.02 m
V = 10 000 x 0.02
V = 200 m/s
Question: A wave has a speed of 500 m/s and a frequency of 200 Hz. Calculate the wavelength.
Answer: λ = v / f
λ =
Λ = 2.5 m
Draw diagram.
Method to measure the speed of sound waves in the air:
Separated by a distance of 500 m, Person a is holding a pair of cymbals and Person B is a timer.
Person B starts timing when she sees Person A clash the cymbals together. Person B then stops the
timing when she hears the sound of the cymbals clashing. The speed of the sound waves then can be
calculated by dividing the distance travelled by the time taken.
Problems with the experiment: every person has a different reaction time. It takes a fraction of a
second between seeing the cymbals and starting the timer as well as hearing the sound and stopping
the timer. This error can be reduced by having a large number of observers with timers. We take all
their results and discard any anomalies and then calculate a mean value. The time between seeing
the cymbals clash and hearing the sound is very short making it difficult to press the time at the
correct times. This can be reduced by increasing the distance between the two people. The longer
the distance the longer the time. That makes it easier to start and stop the time at the correct times.
Required Practical: Ripple Tank
Draw diagram.
A ripple tank is used to observe the features of water waves. A ripple tank is a shallow tray of water.
In the water is a vibrating bar. The bar is connected to a power pack. When the bar vibrates, it
creates waves across the surface of the water. Above the ripple tank is the lamp and below the tank
is a sheet of white paper. When light shines through the water, it produces an image of waves on the
paper. We use this set up to measure the wavelength, frequency and speed of the water waves. Th
easiest way to do this is to record the waves using a mobile phone, it allows us to play back the
recording at different speeds or to freeze the image completely.
,To measure the wavelength, place a ruler on the paper. Then freeze the image of the waves. Now
measure the distance between one wave and 10 waves further (total of 10 wavelengths). To one
wavelength, divide this by ten.
To find the frequency, place a timer next to the paper and count the number of waves passing a
point in a second. It is more accurate to count the number of waves in 10 seconds and then divide by
10. This is easier if recorded and then watched in slow motion. Remember to record the time as well
as the waves.
We already know the wavelength and the frequency of the waves; we can use the wave equation to
determine the speed. Another way to determine the wave speed is to select a wave and measure
the time it takes to move the length of the tank. Calculate the speed by dividing the distance
travelled by the time taken. Might get slightly different results using these two methods because of
measurement errors e.g., timing.
Required Practical: Waves in a Solid
Draw diagram.
String with one end attached to a vibration generator. At the other end of the string is a hanging
mass which keeps the string taut. The vibration generator is attached to a signal generator (which
allows us to change the frequency of vibration of the string). When the power is turned on, the
string vibrates. At a certain frequency, we get a standing wave. This is due to an effect called
resonance. Standing waves are found in stringed musical instruments such as a guitar. The
wavelength of the standing wave is measured using a ruler. We need to measure the total length of
the standing wave from the wooden bridge to the vibration generator. This can be used to calculate
the speed of the wave using the wave equation. The frequency is read from the signal generator.
Draw diagram.
If the frequency is increased, at a certain frequency the standing waves change to 3 half
wavelengths. To calculate the wavelength of this, we need to divide the total length by the number
of half wavelengths and then multiply by 2.
The wave speed of the string does not depend on the frequency or the wavelength. The wave speed
depends on the taughtness of the string and the mass / cm.
Reflection of Waves
Draw all diagrams.
When a wave hits a boundary with a different material e.g., glass, the wave could simply be
transmitted through the material, the energy of the wave could be absorbed by the material (if that
happens, then the wave may not pass through the material at all) or the wave may simply be
reflected off the surface of the material. The surface of a material can transmit, absorb or reflect a
wave. Which of these happens depends both on the material and the wavelength of the wave.
In certain case, waves can change direction when they pass from one material to another. This is
called refraction.
Light reflecting off the surface of a mirror.
Draw diagram.
, The incident ray is a ray of light striking the surface of the mirror. The arrow shows the direction of
the ray. Start by drawing the normal (a dotted line at right angles to the surface of the mirror). Then
measure the angle between the incident ray and the normal. This is called the angle of incidence.
Draw a reflected ray. The angle of reflection equals the angle of incidence.
Draw diagrams.
Required Practical: Reflection and Refraction
Equipment: ray, box, lens and slit. This produces a narrow ray of light. Ray boxes get hot so it’s
important to switch them off when they are not being used. This practical could also be done using a
laser but that can be more dangerous so a ray box is safe.
Draw diagrams.
First take a piece of A3 paper and draw a straight line down the centre using a ruler. Then use a
protractor to draw a line at right angles. This is the normal. Now place a glass block against the first
line so that the normal is near the centre. Now draw around the glass block. At this point, turn out
all the lights in the room. Next use the ray box to direct a ray of light so it hits the block at the
normal. This is the incident ray. The angle between the incident ray and the normal is the angle of
incidence. Now adjust the ray box to change the angle of incidence. At a certain angle, we can see a
ray reflect from the surface of the block. We can also see another ray leaving the block from the
opposite side. This is the transmitted ray. Now mark the path of the incident ray and reflected ray
with crosses and the transmitted ray.
Now turn on the room lights and switch off the ray box. Finally, remove the glass block. Now draw in
both the incident ray and the reflected ray. Next draw in the transmitted ray so it meets the position
of the block. Draw a line to show the path of the transmitted ray through the glass block. Now use a
protractor to measure the important angles. Both the angle of incidence and angle of reflection need
to be measured, then the angle of refraction (the angle between the normal and the path of the
transmitted ray through the block).
Now do the whole experiment again but use a block made from a different material e.g., a plastic
such as Perspex.
What you should find out is that the angles of incidence and reflection are the same for both glass
and Perspex because the angles of incidence and reflection do not depend on the material.
However, the angle of refraction will be different with Perspex than with glass because the angle of
refraction is different for different materials.
Sound Waves
Sound is a longitudinal wave. When sound waves move through air, the air particles vibrate from
side to side. These vibrations can pass from one medium to another e.g., air to a solid.
Sound waves can travel through solids causing vibrations in the solid. Sound waves can only move
through a medium e.g., air or solid as the waves move by particles vibrating. Sound waves cannot
pass through a vacuum as there are no particles. Just like light, sound waves can be reflected. A
reflected sound wave is called an echo.
Within the ear, sound waves cause the ear drum and other parts to vibrate which causes the
sensation of sound. The conversion of sound waves to vibrations of solids works over a limited
frequency range. This restricts the limits of human hearing. Partly because of that, normal human
