BLOCK 3 WAVES
Topic 3.1 General Properties of Waves
By Zainul Arfeen
Wave motion
A wave transmits energy from one place to another.
For example, energy can be carried by a water wave
generated by a boat out at sea to the shore, or by a sound
wave from the loudspeaker to an audience’s ears.
The most common waves found in daily life are
water waves, sound waves and electromagnetic waves.
A Wave
 Waves transfer energy from one place to
another
 The disturbance moves along the wave not the
particles
A wave in the sea:
• disturbance is molecules of water going up and down
• medium = water
There are two types of waves:
Transverse wave
Longitudinal wave
Transverse wave
A transvers wave is a wave in which the vibrations of the
particles are perpendicular to the direction of travel of
the wave.
Transverse wave can illustrate by vibrating ropes and
springs as shows below.
In order to produce transverse wave by using rope, one end of the
rope should be attached and from the other end the rope must move
up and down as shown below.
So the vibration of the rope is perpendicular to the direction of wave
travels.
Note that the waves are carrying energy from one
place to another but the water particles are not
transferred.
previous
next
ENERGY
speed
VIBRATIONS
The speed is how fast the disturbance travels
(how fast the energy is transferred)
speed
ENERGY
speed
Notice that both waves have the same speed bu
different wavelengths and frequencies. The wav
equation can explain this mathematically.
To produce transverse wave by using spring one student
can hold spring while another student can move spring left
and right as shown below. So the vibration of the spring is
perpendicular to the direction of wave travels.
Examples of transverse wave: water wave and all the
electromagnetic waves.
(radio waves, microwaves, infra-red, visible light, ultra-violet,
X-rays and gamma-rays).
Amplitude
 maximum disturbance caused by a wave
 measured from the middle to a Crest or trough
 symbol: a
 units: m
Wavelength
 The length of one complete wave
 peak to peak/crest to crest/trough to trough
 Symbol: λ
 Units: m
Transverse Wave
 The disturbance is perpendicular to the direction of
movement
 Example Light
Amplitude
The amplitude of a wave is the maximum displacement of the wave
from its rest position.
Wavelength (λ)
The wavelength of a wave is the distance between two successive crests
or troughs. Or the distance of one complete wave.
Which of the points is exactly one wavelength
away from point A?Answer is E
A
B
E
C
F
G
D
The next 5 tasks will test to see if you have
understood the idea of wavelength
1 Match the highlighted letter to one which is e
one wavelength away from it.
A B C D E F G H I J K L M N O P Q R S T U V WX
2 Match the highlighted letter to one which is e
one wavelength away from it.
A B C D E F G H I J K L M N O P Q R S T U V WX
3 Match the highlighted letter to one which is e
one wavelength away from it.
A B C D E F G H I J K L M N O P Q R S T U V WX
4 Match the highlighted letter to one which is e
one wavelength away from it.
A B C D E F G H I J K L M N O P Q R S T U V WX
5 Match the highlighted letter to one which is e
one wavelength away from it.
A B C D E F G H I J K L M N O P Q R S T U V WX
Frequency
 Number of waves per second
 Either passing one point or generated
 Symbol: f
 Units: Hz (s-1)
Count the number of complete
vibrations
in ten
Frequency
= 1 Hertz
seconds and then work out the frequency of this wave
Frequency = 1.4 Hertz
Ten second timer
Frequency = 0.5 Hertz
Period
 This is the duration of a wave
 How long it takes for one wave to occur
 Symbol: T
 Units: s
Frequency and speed of the
Frequency
wave
The frequency of a wave is the number of complete waves
produce in one second. It is measured in Hertz (Hz).
𝟏
Frequency can be calculated by using the formula: 𝑭 =
𝑻
Speed of the wave
The speed of a wave is the distance travelled by any point
on the wave in one second.
The speed of the wave can be calculated by using the wave
equation:
Speed = frequency × wavelength, V = f λ
Wave equation
Wave speed, wavelength and frequency are
related by the wave equation
The Wave Equation
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
V
f

Example Question
Diagram below shows how the displacement of water wave
varies with time. The wavelength of the wave is 8.0 cm.
(a) State the amplitude of the wave.
Ans: 2 mm
(b) Calculate the frequency of the wave.
𝟏
𝟏
Ans: 𝑭 =
𝑭=
= 2Hz
𝑻
𝟎.𝟓𝟎
(c) Calculate the speed of the wave.
Ans: V = f λ = 2 × 8 = 16 cm/s
Example Question
A radio station broadcasts on a wavelength of 250m. The
speed of radio waves is 3 × 108 m/s. calculate the frequency
of the wave.
Ans: V = f λ
f = V/ λ = 3 × 108/250 = 1200 000 Hz
or 1200 kHz.
Longitudinal wave
A longitudinal wave is a wave in which the vibrations
of the particles are parallel to the direction of travel
of the wave.
Longitudinal wave can illustrate by vibrating springs as
shows below.
To produce longitudinal wave by using spring, one student can hold
spring while another student can move spring forward and backward
as shown below. So the vibration of the spring is parallel to the
direction of wave travels.
Example of longitudinal wave: Sound waves.
Compression
Compression is the region where the particles are close together
and has high pressure.
Rarefaction
Rarefaction is the region where the particles are further apart and
has low pressure.
Ripple Tank
A ripple tank is a shallow glass-bottomed tank containing
small amount of water. A light shining downwards trough
the water cast shadow of the ripples on the floor below,
showing up the pattern that they make.
A spherical dipper can produce a different patter of
ripples. The dipper just touches the surface of the water.
As it vibrate up and down, equally spaced circular ripples
spread out across the surface of the water as shown below.
Ripple tank can also be used to demonstrate the reflection
and refraction of water wave.
One way of making ripples on the surface of the water in a
ripple tank is to have a wooden bar that just touches the
surface of the water. The bar vibrates up and down at a
steady rate. This sends equally spaced straight ripples
across the surface of the water as shown below.
Reflection
Reflection of wave
Reflection of the water wave can be demonstrated by
putting metal barrier on one side of ripple tank. When the
straight ripples (‘plane waves’) strikes the flat surface of the
barrier, the ripples bounce off (reflected) as shown below.
The ripples are reflected by the metal barrier so that angle
of incidence is equals to angle of reflection.
Water waves
are reflected
by the barrier
Barrier
The lines in the diagram shown above are called wavefronts.
The separation of the wavefronts is equals to wavelength of
the ripples.
Line joining points of same phase is called Wavefronts.
OR
A line joining all the crests or troughs is called the
wavefronts.
Refraction
Refraction of wave
Refraction of the water wave can be demonstrated by
immersing the glass plate into the ripple tank to make the
water shallower in that part of the tank. When the straight
ripples produce by the tank moves from the deep region to
shallow region, it changes the speed
Ripple tank
model
The waves slow down
when they reach the
shallow water
Deep water
The wavelength gets
shorter
But the frequency
stays the same
Shallow water
Can you understand
what is happening
here? HINT remember
the wave equation
Water waves
Deep water
Shallow water
If the waves reach the
shallow water at an
angle the waves still
slow down.
The waves also
change direction.
We call this effect
refraction.
When the wave is travelling from deep region
to shallow region it refracts, because the
speed of the wave decreases. So the
wavelength of the wave also decreases but the
frequency of the wave remains constant.
R
T
C
O
F
A
ID
N
I
• Diffraction is the spreading out of waves at
edges and gaps.
• All types of waves can be diffracted.
• The amount of diffraction is affected by the
size of the gap and the wavelength.
Diffraction of water waves
Small amount of
spreading (diffraction)
The wavelength of the
waves is much smaller
than the size of the gap
The wavelength is the
same size as the gap
so there is very good
spreading (diffraction)
For Edges
Long wavelengths diffract more than short
wavelengths.
For Gaps
The wavelength should be the same size
as the gap to get good diffraction.
Diffraction of sound waves
Speed of sound in air = 330m/s
Typical frequency = 440Hertz
Work out the wavelength of these sound waves
Speed = wavelength x frequency
Wavelength = speed/frequency
Wavelength = 330/440
= 0.75metres
About the same size as the width of a door
Diffraction of light waves
To get spreading (diffraction) of the light
the gap it passes through has to be very
small-because the wavelength of light is
very small
Diffraction of
radio waves
This transmitter is producing
radio waves
This house is in the
shadow of some hills
The aerial is on a pole
to try and improve the
reception of radio waves.
Will the people living here
be more likely to receive
long wave or short wave
radio programmes?
Short radio waves are hardly
diffracted over the top of the hill.
Short wave radio signals do not
reach the aerial
Long wavelength radio waves can be
diffracted over the top of the hill.
The hill acts rather like an edge
causing diffraction
Long wavelength radio waves
are received by the aerial
Questions on
diffraction
You are having difficulty with the signal strength on your
short wave radio because…
Helpful words/phrases to use: long wavelength
short wavelength, diffracted, gap, edge.
Copy and complete the diagrams to illustrate your
answer.
B
A
C
D
Which of these show how rays are
(a) reflected?
(b) diffracted at a gap?
(c) refracted?
(d) diffracted at an edge?
Which of these show how waves are
(a) reflected?
(b) diffracted at a gap?
(c) refracted?
(d) diffracted at an edge?