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# WAVES

PHYSICS

FORM 5

Chapter 6

Waves

Compiled by In collaboration with

Cikgu Desikan Cikgu Khairul Anuar

SMK Changkat Beruas, Perak SMK Seri Mahkota, Kuantan

Chapter 6

Waves

Dear students,

You see, God helps only people who work hard. That principle is very
clear.

~A. P. J. Abdul Kalam

FORM 5 PHYSICS
Learning Objectives :

1. Understanding waves 5. Analysing interference of waves
2. Analysing reflection of waves 6. Analysing sound waves
3. Analysing refraction of waves 7. Analysing electromagnetic waves
4. Analysing diffraction of waves
2016 2007 2008 2009 2010 2011 2012 2013 2014 2015

Analysis of Past Year Questions

P1 6 6 6 8 7 6 4 7

A 1 1 1 2 1 1 - 1

P2 B - - - 1 - 1 - -
C 1 1 - - - - - 1

A - - 1 1 - 1 - -
P3
B - - - - 1 - 1 -

Chapter 6

Waves

Dear students,

Either you run the day or the day runs you.

Concept Map

Wavefront Waves Oscillating/ Vibrating system

Loss of energy
Propagation

Types of waves Displacement, y Damping
Amplitude, a
Longitudinal Transverse
Frequency, f
Example Wavefront, λ Resonance

Sound Water Light Electromagnetic Formula

Speed Graph
phenomena
Properties V=fλ

Pitch Reflection Refraction Spectrum y - t y - s

Loudness Diffraction Interference

6.1 Waves

What is waves ? How do waves transfer energy?

a disturbance or variation that transfers When energy is transferred by a wave
energy progressively from point to point in from a vibrating source to a distant

a medium receiver, there is no transfer of matter

between the two points.

Type :

• Sound
by vibrating mechanical bodies Example

such as a guitar strings or a
tuning fork

• Light
result of vibrations of electrons in

an atom

• Water
by a disturbance on a still water
surface When the string is shaken up and down, a

disturbance moves along the length of the

string. It is the disturbance that moves
along the length of the string, not parts of

the string itself.

4

Example

 Drop a stone in a quite pond.
 It will produce a wave that moves out from the center in expanding circles.

 It is the disturbance that moves, not the water.
 After the disturbance passes, the water is where it was before the wave was produced .

Wave moves outwards

Cork moves up and down as
the wave passes

source
The energy transferred from a ____________________(the stone) to a ___________
matter
(the cork) which does not involve the transfer of ___________(water).

The string and water is the medium through which wave energy travels.

5

What is Transverse Wave ?

A wave in which the vibration of particles in the medium is perpendicular to the direction of

propagation of the wave.

direction of wave
side to side propagation

movement

fixed

end

direction of vibration
of particles

The motion of the particles medium (spring) is at right angles to the direction in which the wave
travels.

Example

1. Water waves

2. Light waves

6

What is Longitudinal Wave ?

A longitudinal wave is a wave which the vibration of particles in the medium is parallel the
direction of propagation of the wave.

backwards and
forwards movement

direction of wave

propagation

fixed

end

rarefaction rarefaction

direction of vibration of
particles

The particles of the medium (spring) move along the direction of the wave. The wave that travels
along the spring consists of a series of compression and rarefaction.

Example

1. Sound waves

7

Direction Direction

Process of
the vibration of the vibration of
transferring
particles in the energy from one particles in the
medium is medium is parallel

perpendicular to location to to the direction of
the direction of another propagation of the

propagation of the wave.
wave.

Transverse Produced by an Longitudinal

Waves oscillating or Waves
vibrating motion
Example Example

Water waves

Sound waves
Light waves Does not involve
the transfer of

matter

8

What is a ripple tank?

The phenomenon of water waves can be

investigated using a ripple tank.
Lamphouse

The water waves are produced by a
vibrating bar on the water surface. To cell and
The tank is leveled so that the depth of rheostat

water in the tank is uniform to ensure water Down for circular
waves propagate with uniform speed waves
Straight wave Stroboscope
dipper
Rubber
Band

Eccentric Sponge

beach

Water

Plane waves

Wave pattern on
white screen

Circular waves
9

The water acts as a lens to produce a pattern of
crest light from lamp bright and dark regions on a piece of white

paper placed under the tank when light passes
through it.
trough
Water waves have crests and troughs.

water Crest
the highest position of the wave acts as a
convex lens

Trough

the lowest position acts as a concave lens.

Light rays from the lamp on top will focus onto

screen the white screen below.
dark bright dark bright dark

Bright lines correspond to the crests.

Dark lines correspond to the trough.

10

Wavefronts are lines joining Direction of propagation

all points vibrating at the Q S U V
same phase and of equal
distances from the source of

the waves. Plane Ripple tank

Dipper Water Wavefront

The wavefronts of both
transverse wave and

longitudinal wave are P R T U Crest
perpendicular to the
direction of propagation of Trough

the waves.

Wavefront

2. Circular wavefronts
1. Plane wavefronts

Q S U W
Direction
Direction of

of propagation
propagation
Direction

P R T V of propagation
11

Vibration/Oscillation Amplitude (a)
The movement from one
extreme position to the other The maximum

and back to the same displacement from its
position equilibrium position.

Amplitude relates to

loudness in sound and
Waves brightness in light.

SI unit: meter, m

Wavelength (λ)
The distance between two adjacent points of
the same phase on a wave.

λ λ

λ λ

The distance between two successive The distance between two successive
crests or two successive troughs compressions or two successive

rarefactions in a sound wave. 12

Period (T) Frequency, f

The time taken for an The number of waves produced in

oscillation to complete one one second.
cycle. 1

SI unit is second (s). f =
Waves T

SI unit is Hertz (Hz)

Wave Speed (v) Relationship
The speed of a wave is the The relationship between speed,

measurement of how fast a crest is wavelength and frequency
moving from a fixed point.
v=fλ

-1
SI unit is ms .

Displacement-distance graph Displacement-time graph

Displacement Displacement
λ T

a a T

Distance Time
a a
λ T

13

Exercise 6.1.1

1. Determine wave length and amplitude from 3. A whistle produces a sound at a frequency of
the graph given below. 400 Hz. If the speed of the sound is 600ms ,
-1
determine the wavelength of the sound
Displacement
18 cm wave.

λ = 1.5 m

Time
5 cm

λ = 12 cm
a = 2.5 cm 4.
12 cm

2. A slinky spring vibrated to generate
longitudinal waves.

40 cm
Determine wave length of water wave from

the diagram given above.

λ = 1.5 cm

20 cm
The wavelength of the waves is _________.

14

5. The figure shows the waveform of a slinky 6. Determine the frequency of the wave.
spring which vibrated at a frequency of 8 Hz.
Displacement/ m
Displacement/ m

6
10

2.0 distance/ m 1.0 Time/ms

-6
10

2000 Hz
Determine
a) amplitude 5 m
b) wavelength 1.0 m

c) wave speed 8 ms -1
7. The circular waves produced by a vibrating
sphere dipper with a frequency of 5 Hz.

What is the wave speed of the wave.

7.5 cms -1

4.5 cm

15

Damping
Graph
Damping process is a process of losing
energy in a vibrating/ oscillating system Displacement

in the form of heat.

The amplitude of an oscillating system will
gradually decrease and become zero when

the oscillation stops. Time

Causes

 To enable an oscillating system to go on
1. Loss of energy in the system to continuously, an external force must be
overcome frictional forces or air

resistance → applied to the system.
External damping .
 The external force supplies energy to the

forced
system. Such a motion is called a _________
2. Loss of energy due to the extension oscillation
________________.
and compression of the molecules in
the system →
Internal damping .  The frequency of a system which oscillates
freely without the action of an external force is

called the natural frequency .

16

Resonance

Resonance occurs when a system is made to oscillate at a frequency equal to its natural frequency
by an external force.
The resonating system oscillates at its maximum amplitude.

Good Effects

1. The tuner in a radio or television enables us to select the programmes we are interested. The

circuit in the tuner is adjusted until resonance is achieved, at the frequency transmitted by a
particular station selected. Hence a strong electrical signal is produced.

2. The loudness of music produced by musical instruments such as the trumpet and flute is the
result of resonance in the air.

1. A strong wind can cause a bridge to vibrate
at a frequency equal to its natural frequency.

The bridge will collapse as it vibrates with
maximum amplitude.

2. A soprano singer singing at
a frequency equal to the
natural frequency of

vibration of the glass.
Maximum vibration will cause the glass
Tacoma Bridge shattered into pieces.
17

Experiment in Barton’s pendulum

What happens when pendulum X is made to oscillate?

• When pendulum X is swung into oscillation, all the other

pendulums swing.
• Pendulum D swings with maximum amplitude.
• This is because, the length of the pendulum X = length of

the pendulum D.
• The frequency of oscillation of the pendulum X =

frequency of oscillation of the pendulum D.
• Resonance has occurred in pendulum D and caused it to
swing with maximum amplitude.

Exercise 6.1.2

1. The figure shows a simple pendulum with a mass of
40.0 g and a length, L of 20.0 cm. The pendulum

makes 20 complete oscillations in 18.80 seconds.
Relationship between period of oscillation, T of the
simple pendulum with its length, L is expressed in the

formula below as :

C A Highest L where g is gravitational
Lowest B Position T= π2
Position g acceleration.

18

a) Using the letters A,B and C from the figure, state
i. the equilibrium position

B

ii. the order of the positions of pendulum bob in a complete oscillation.

C → B → A → B → C / B → A → C → A → B / A → B → C → B →A

b) Calculate period of oscillation of the pendulum.

0.94 s

c) Calculate frequency of oscillation of the pendulum.

1.06 Hz

d) What happens to the frequency of the pendulum when pendulum bob with a mass of
50.0 g is used.

No change

19

e) Determine the frequency of the pendulum when the length of pendulum, L is increased to
80 cm.
0.563 Hz

f) After oscillating number of times, the pendulum finally stops. Why?

Mengalami pelembapan

g) Sketch a displacement- time graph to show the oscillations of the pendulum untul it stops.

Displacement

Time

h) State the types of energy of pendulum when it located

i. at B
Kinetic Energy

ii. at C

Gravitational Potential Energy

iii. between B and C

Kinetic Energy and Gravitational Potential Energy

20

6.2 Reflection of waves

• Reflection of waves occurs when a wave Lamphouse

strikes an obstacle.
• The wave undergoes a change in direction To cell and

of propagation when it is reflected. rheostat
• The value of frequency (f), wavelength Down for circular
waves
(λ) and speed (v) remain the same after Straight wave
reflection. dipper
Rubber
Law of Reflection: Band

Incident angle, i = Reflected angle, r Reflector Sponge

beach
Incident wave : Water

the wave before it strikes the
obstacle
Reflected wave: Complete the diagrams to show reflection of water

the wave which has undergone a waves.
change in direction of propagation white screen

after reflection. a) b)

i = angle of incident – the angle

between the direction of propagation
of incident wave and the normal

r = angle of reflection – the angle
between the direction of propagation

21

6.3 Refraction of waves

Refraction of waves After refraction, the wave has the same,

a phenomenon in which the direction of but a different speed, frequency and
propagation of a wave changes when direction of propagation.

passing from one medium to another Lamphouse
medium.

The change in the direction of wave occurs To cell and
when there is a change in the speed of the wave rheostat

at the boundary of two mediums. Down for circular
waves
The relationship between v and λ of a Straight wave
water wave in deep and shallow water: dipper
Rubber
v = f λ f is constant Band

Plastic
v is directly proportional to λ plate Sponge
beach
v v 1  v 2 Water

= k
f f 1 f 2

v 1 v 2 v > v 2
1
λ 1 λ 2 λ > λ 2
1
white screen
Shallow water
Deep water Deep water

Plastic plate 22

Shallow water

Depth↓ Frequency Normal Depth ↑

Deep Normal unchanged Shallow Deep
water water water

Wave
v ↓ Speed v ↑

Water waves changes Water waves

passes from passes from
deep water to shallow water to

shallow water deep water

λ ↓ Wavelength λ ↑
changes

refracted refracted away
toward the Angle of from the
normal Refraction normal
changes

23

Complete the diagrams which show refraction of water waves.

1) 4)

Deep Shallow Deep Deep Deep

2) Shallow
Shallow Deep

5)

Deep

3) Deep Deep

Shallow

Deep Shallow Deep
24

Exercise 6.3

1. A plane wave has a wavelength of 2 cm 2. The diagram shows a plane water wave
-1
and a velocity of 8 cm s as it moves over moving from one area P to another area Q
the surface of shallow water. When the of different depth.
plane wave moves into an area of greater
-1
depth, its velocity becomes 12 cm s . P Q
What is
a) the wavelength

b) the frequency of the wave in the area
of greater depth? 12 cm 12 cm
a) 3 cm

b) 4 Hz If the speed of water wave in P is 18 cms ,
-1
what is the speed of water wave in Q?

9 cms -1

25

6.4 Diffraction of waves

Diffraction Of Waves

A phenomenon in which waves spread out as they pass through a aperture/ gap or round a

small obstacle.

Frequency, wavelength and Factors that influence
speed of waves do not the effect of diffraction
change.

Changes in the

direction of
Saiz of
propagation and Characteristics of Saiz of gap or wavelength
obstacle
the pattern of the diffracted waves
waves.

The effect of diffraction is obvious if:
1. the size of the gap or obstacle is
The amplitude of the __________________________.
small enough
diffraction wave

decreases (its energy 2. the wavelength is _____________
large enough
decrease).
_________________________

The effect of diffraction is obvious if the shape of the diffracted waves more spread out or

more circular. 26

Pembelauan Gelombang Air Pemerhatian

(a) Celah lebar

The waves are bend only at the
Lampu
edges after passing through the gap.

The effect of diffraction is not obvious

ke bekalan kuasa
dan rheostat

Pencelup
sfera Stroboskop
Pencelup

Gelang satah
getah

(b) Celah sempit
Tebing
Obstacle spon Gelombang membulat dan kelihatan

Air berpunca dari celah kecil. Kesan

Skrin putih

27

(c) Large Obstacle (d) Small Obstacle

The waves only curved at the edge The waves only curved at the edge

which adjacent to the barrier after which adjacent to the barrier after
passing the obstacle. The effect of passing the obstacle. The effect of

diffraction is not obvious. diffraction is obvious.

***
As the size of the gap or obstacle is smaller, the effect of diffraction becomes obvious.

28

Diffraction of Light

a) Single Slit b) Pin hole

alternate

bright bands and dark bright and
bands of different width. dark ring

passing the pin

hole
Light

out behind
the slit

Laser beam

1. Light is diffracted if it passes through a

narrow slit comparable in size to its
0.1mm
wide slit wavelength.
2. However, the effect is not obvious as the

size of the slit increases.
3. This is because the wavelengths of light are
Laser beam
very short.

29

The effect of wavelength and the size of the gap on the pattern of diffraction of light

a) Wavelength b) Size of aperture/ gap

The wavelength of red light is greater than blue The size of the gap in the diagram (ii) smaller

light. than the size of the gap in the figure (i).

The effect diffraction is more obvious when the The effect diffraction is more obvious when the

wavelength is greater. size of gap is smaller.

30

Diffraction of Sound

Cleaner

Cleaner

A cleaner can hear the sound of a radio placed nearby a corner of a wall but he cannot see

1. The cleaner can hear the radio even behind obstacles.

2. Sounds from radio to spread around the corner of the wall because of the diffraction of sound
waves.
3. The waves will experience a diffraction when pass through a single aperture or round an

obstacle.
4. Sound waves are more easily diffracted compared to light waves.

-7
5. This is because the wavelength of sound is much larger than the wavelength of light (~ 10 m).

31

Piccolo

If a marching band is approaching on a cross street, which instruments will you hear first?

1. Low pitched bass drum has long wavelength.
2. High pitched piccolo has short wavelength.

3. High pitched sound tend to be more directional because they don’t diffract as much.
4. Therefore, sound from bass drum heard first.

32

6.5 Interference of waves

Interference of waves

A phenomenon of waves which occurs a result of superposition of waves.

33

How does interference occur?

• Wave interference occurs when
two waves meet while propagating Lamphouse

along the same medium.
• When the two waves are
superposed, interference will occur To cell and

either constructive interference or rheostat
destructive interference.
spherical
dippers
coherent sources

Coherent sources are sources that Rubber
Band
produce wave having the same
frequency and a constant phase
difference,  . Sponge
beach

Water

s

t white screen

34

Principle of superposition of Waves

When two waves interfered, the resulting displacement of the medium at any location is the

algebraic sum of the displacements of the individual waves.

Superposition of two waves originating from two coherent sources.

Constructive Interference

Superposition of two crests Superposition of two troughs

Resultant
Amplitude
Cork Cork

2a
a a

Resultant
Destructive Interference Amplitude

Superposition of a crest and a trough

Resultant
Amplitude
35

Interference of water waves

Interference pattern of water waves produced when two coherent waves superposed.

S 1

S 2

1. S and S are the sources of coherent waves.
1
2
2. Water wave interference pattern shown is the result of constructive interference and destructive
interference occurs.
3. For ease of discussion, the wavefront of the crests is represented by a full line while the

wavefront of the troughs is represented by a dotted line as shown in the diagram on the next
page.
36

Interference of Waves

Constructive Interference Destructive Interference

Constructive interference occurs when two Destructive interference occurs when two

waves at same phase (two crests or two waves at out of phase (crest of one wave with
troughs) coincide to produce a wave with the trough of the other wave) coincide, thus

crests and troughs of maximum amplitude canceling each other with the result that the
(+2a or -2a). resultant amplitude = 0.

Keys : Antinode
• Maximum crest wave (2 crests meet)
× Zero amplitude (trough meets crest) A point where constructive
о Maximum trough wave (2 troughs meet) interference occurs.

Node line Antinode line Node

A point where destructive
interference occurs.

Wavefront (troughs)

Wavefront (crests)

S 2 Waves sources S 1 37

Young’s Formula
Factors affecting the interference pattern

The relationship between λ, a, x and D
The interference pattern depend on the
Node line
x x Antinode line value of x. When x changes, the
interference pattern also changes .

λ α x

λ D

λ D x= x
a

λ
S 1 a S 2 ****Draw graphs 0

ax 1 D α x
λ = x α

D a

x x
a = distance between two coherent sources

λ = wavelength
x = distance between two consecutive node (or
antinode) lines
D = distance from the two sources to the point of 1
measurement of x
0 a 0 D
38

Skrin Interference of Lights

Dwi-celah Occurs when an incident light wave passes
through a double slit.

Celah x An interference pattern is produced as a result
of the superposition of two emerging light waves
from the double slit.

Sumber Young’s double-slit experiment

cahaya x
 Use monochromatic light (light wave with
only one wavelength)

 The double slit must be very narrow (about
Corak Interferens
0.5 mm) to produce a clear interference

Eksperimen dwicelah Young boleh digunakan pattern because the wavelength of light is
untuk mengukur panjang gelombang sesuatu very small.
sumber cahaya dengan menggunakan  When light from monochromatic source

persamaan: passes through a double slit, two sources of
coherent light are produced.
a = Distance between the two
ax slits on the double slit plate  The interference pattern consists of alternate
bright and dark fringes that can be seen on a
λ = D =Distance between the distant screen.
D double-slit plate and the
screen
λ = The wavelength of light  Bright fringes : Interferens membina
(depends on its color.)  Dark fringes : Interferens memusnah
x = Distance between two
consecutive bright fringes or
dark fringes.
39

Interference of Sound Wave 1. The two loud speakers are the sources of the
two coherent sound waves as they are
Occurs when two coherent sound waves
connected to the same audio signal generator.
interact on the basis of the principle of 2. A student will hear alternating loud and soft
superposition to produce a pattern of sounds as he walks along the straight path

alternating loud and soft sounds .
(XY) at a distance of D from the
loudspeakers.

3. The alternating loud and soft sounds is
caused by interference of the sound waves.
Loudspeaker
X
Interference
K
Audio signal L pattern
generator K

Audio signal generator L K = Loud sound

K
L = Soft sound
L

K

L

Loudspeakers K
Y Loud sound:
a= the distance between the two loudspeakers

Constructive Interference
ax D =Distance between the loudspeakers and the path _________________________
along which interference can be detected
λ = λ = The wavelength of sound waves is influenced by the Soft sound :
D frequency of the audio signal generator.
Destructive Interference
x = Distance between two consecutive positions where _________________________
loud sound is heard 40

Exercise 6.5

1. In the interference of two coherent sources 2. In a Young’s double slit experiment, the

of waves, the separation between two distance between the double slit and the
spherical dippers is 3 cm and the distance screen is 4.0 m and the separation of the

between two consecutive node lines is 4 cm two slits is 0.5 mm. Calculate the distance
measured at a distance of 15 cm from the between two consecutive bright fringes for
-7
two coherent sources of waves. Calculate violet light with a wavelength of 4.0 x 10 m.
the wavelength of the water waves 3.2 mm
originating from the sources.
0.8 cm

41

3. The wavelength of light can be determined 4. In an experiment on the interference of

with a double-slit plate. waves, two loudspeakers are placed at a
distance of 1.5 m from each other. They
are connected to an audio signal generator

to produce coherent sound waves at a
frequency of 0.5 kHz. Calculate

(a) the wavelength of the sound wave if
the speed of sound is 300 ms -1
(b) the distance between two consecutive

soft sounds at a perpendicular
14 mm
distance of 5 m from the source of the
The diagram shows the pattern of sound. a) 0.6 m
interference fringes obtained in a Young’s b) 2 m
double-slit experiment. The separation of

distance of the two slits is 0.25 mm and the
distance between the screen and the

double slit plate is 3.0 m.
Calculate the wavelength of light used in

the experiment.

1.67 x10 m
-7

42

6.6 Sound waves

1. Sound is a form of energy propagated How is sound produced by a vibrating
as waves that make our eardrums
objects ?
vibrate.

2. Sound waves are caused by  Sound waves are produced when a vibrating
vibrating objects. object causes the air molecules around it to

3. Sound waves are longitudinal waves. vibrate.
 When a tuning fork vibrates, layers of air

vibrate and the sound energy is propagated
through the air around it in the form of waves.

How the loudness relates to amplitude?  When the tuning fork moves forwards, the air
is compressed.
The loudness of the sound depends on its  When the tuning fork moves backwards, the

amplitude. air layers are pulled apart and cause a
If the amplitude is increased, the loudness rarefaction.
increases.  Therefore, a series of rarefactions and

compressions will produce sound.

How the pitch relates to frequency ?

direction
A high pitch sound corresponds to a high λ propagation
frequency and a low pitch sound Vibration

corresponds to a low frequency of vibration.

compression rarefaction

Tuning Fork
43

Relationship between amplitude and Relation between pitch and frequency of
loudness of sound sound

The audio signal generator is switched on and The audio signal is switched on and the

the frequency of the sound wave is adjusted to loudness is adjusted to a suitable level. The
a suitable level. The loudness of the sound is frequency of the sound is varied from low to

Observation of the shape of the sound wave Observation of the shape of the sound wave
displayed on the screen of oscilloscope. displayed on the screen of oscilloscope.

Amplitude of Loudness Wave form Frequency of Pitch of
Wave form sound wave sound
sound wave of sound

High High Low Low

Medium Medium Medium Medium

Low Low
High High
Write : Low / Medium / High

Write : Low / Medium / High
CRO

Audio signal
generator Microphone

Loudspeaker 44

Applications of reflection of sound waves

• Ultrasound waves is used to scan and capture the Sonogram

image of a fetus in a mother’s womb and the image of
internal organ in a body. R

• Transmitter P emits ultrasound downwards to the Transmitter, Detector
fetus. P
• Detector R receives the ultrasound (echoes) reflected Abdomen

by the various parts of the fetus.
• The soft tissues of the fetus absorb most of the

incident ultrasound, reflect very little.
• The bony parts will absorb very little, but reflect most Fetus
of the ultrasound.

• The reflected ultrasound will produce an image of
contrasting brightness.

Sonogram
Image

45

Sonar

• SONAR (Sound Navigation And Ranging) used to

locate underwater objects or to measure the depth of a
seabed. ship
• The ultrasonic waves (sound waves frequency>

20,000 Hz) used in this technique.
• The ultrasonic waves emitted from the transmitter and

reflected by objects on the seabed. Then reflected
• Time interval, t between emission and reception of the

ultrasonic wave signal measured using electronic Receiver Transmitter
devices.

• If the speed of the sound waves, v is known, the depth
of the seabed, d can be measured by using the
formula: seabed

vt d = depth of seabed
d= v = speed of sound wave in water

2 t = time interval

CRO used to determine the time
interval, t

46

A bat can navigate in darkness

• When ultrasonic waves emitted by the bat hit an
object, they are reflected back and received by the

bat.
• The time between the emission of the sound

waves and reception of the reflected waves
enables the bat to estimate the position of the
object accurately.

• This enables the bat to adjust its direction to avoid
knocking at the object.

Human echolocation lets blind man 'see‘!!!

Exercise 6.6

1. An ultrasonic wave is used to determine the depth of a seabed. A pulse of ultrasound is
generated and travels to the seabed and reflected by it. The time taken by a pulse of ultrasonic
-1
wave to travel to and fro the seabed is 0.28 s. It the speed of sound in the water is 1 500 ms ,
calculate the depth of the seabed.

210 m

47

6.7 Electromagnetic Waves

Electromagnetic spectrum

long medium short micro infra red light ultra X-rays gamma

waves waves waves VHF UHF waves violet rays

1000 m 1m 1mm 1 x 10 -3 1 x 10 -6 1 x 10 -9
mm mm mm

Increasing frequency
frequency ↓ frequency ↑

Increasing wavelength
wave length ↑ wave length ↓

• Electromagnetic spectrum is the full range of electromagnetic waves, arranged in decreasing
wavelength (longest to shortest).
• It consists of radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X – rays and

gamma rays.
• Radio waves have the longest wavelength but are of low frequency waves. They carry very little

energy.
• Gamma rays have the shortest wavelength but are of high frequency waves. They carry very
high energy.

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Electro- Magnetic Waves

It is produced when electric and magnetic field vibrate at right angle to each other. The direction
of propagation of the wave is perpendicular to both fields .

Electric field, E

Electric field

Direction of

propagation

Magnetic field
Magnetic field, B

Properties Of Electro-magnetic Waves

• They transfer energy from one point to another.
• They are transverse waves.

• They can travel through vacuum.
• They travel at the same speed through vacuum (speed of light , c = 3 x 10 ms )
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• They all show wave properties such as reflection, refraction, diffraction and interference.
• They obey the wave equation, v = fλ.

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Visible Light

• Visible light waves are the only electromagnetic waves we can see.

• Light can be seen as the colours of rainbow.
• Each colour has a different wavelength.
• Red has the longest wavelength and violet the shortest.

• When all the waves are seen together, they make white light.
• When white light shines through a prism, the white light is broken apart into the seven colours

of the visible light spectrum.
• Red, orange, yellow, green, blue, indigo and violet.

Applications Of Electro-magnetic Waves

Electromagnetic Sources Applications
wave

Gamma Rays Radioactive decay • Engineering – to detect leakages in
underground pipes
• Medicine – cancer treatment

• Food sterilisation

• Medicine

X- rays x-ray tube  X-ray photograph of the internal organs of
the body, e.g to locate bone fracture.
 Cancer treatment

• Engineering – to detect cracks in metal
• Checking of luggage at airports

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