Introduction to Waves
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Part A : Definition
- Definition of waves.
- Basic Properties of waves.
Part B : Types of Waves
and Terminology.
- Mechanical waves :
Transverse and Longitudinal waves.
- Electromagnetic waves.
- Terminology of waves.
Part C : The Wave Equation.
Part D : Common Characteristic of Waves.
Part E : Revision
The basics
PART A
Definition of wave
• A periodic disturbance which travels
through a medium from one point in
space to the others.
Wave motion means the propagation of waves through a medium.
Wave motion appears in almost every branch of Physics.
Basic properties of waves :
• Energy is transferred from one place to another in a
wave motion.
• Motion of the medium (particles of the medium) is
usually periodically vibratory.
• Only the shape or form of wave travels, not the
medium.
Remember to
take notes
PART B
TYPES OF WAVES Waves are classified into different types
according to their natures :
Transverse waves Longitudinal waves
Mechanical waves
Transverse waves
Electromagnetic waves
WAVES
1. Mechanical Waves
• A material medium is necessary for the transmission for
mechanical waves. Mechanical waves cannot travel through
vacuum.
• Due to elastic forces on adjacent layers of medium, disturbance is
transmitted from one layer to the next through the medium.
according to the direction of vibration, waves are also
classified into :
(a) Transverse wave;
(b) Longitudinal waves.
click And ...
Click for
examples
Water waves, sound, vibration of spring, etc.
1.1 Transverse Waves
• The waveform appears in the shape of sine curve.
• A wave in which the motions of the matter particles are
perpendicular to the direction of propagation of the wave itself.
Water waves, pulse in a stretched
string,transverse wave demonstrator.
Examples
1.2 Longitudinal Waves • A wave in which the motions of the matter particles are in the
same direction as the wave propagation.
Examples Sound, or a spring oscillating up and down, etc.Show
magnetic longitudinal demonstrator
2. Electromagnetic Waves • Material medium is not essential for propagation. e/m
waves travel through vacuum.
• Disturbance of electric and magnetic fields travelling
through space.
• All electromagnetic waves are transverse waves.
X-rays, radio waves, micro-waves,etc. examples
Terminology of a Wave
• Amplitude
• Wavelength ()
• Frequency (f)
• Period (T)
• Wave velocity (v)
A wave is usually described by the following terms :
Each term will be explained….
• The amplitude is the maximum displacement of the medium
from its equilibrium position.
• The wavelength () is the minimum distance between two
points which are in phase.
• The frequency (ƒ) is the number of complete oscillations
made in one second.
Unit : Hz
• The period (T) is the time taken for one complete oscillation.
It is related to frequency by T = 1/ƒ
Unit : s Table of
Contents
The Wave Equation
The wave velocity is the displacement traveled by the wave in
one second ……....
The wave velocity (v) is related to
frequency and wavelength by --
v = ƒ The Wave Equation
PART C
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Using the Wave Equation
Example :
A travelling wave of wavelength 0.6m moves at a speed of 3.0 m/s.
What is the period of this wave ?
Click to see the answer
Then the period of this wave is ??? Period T = 1/ƒ
T = 1/5.0 or 0.2 s
Now you know = 0.6 m, v = 3.0 m/s
Can you find the frequency of this wave……
Table of
Contents
By using the wave
equation,
v = ƒ
3.0 = ƒ(0.6)
i.e ƒ = 5.0 Hz
• Transmission of energy
• Reflection
• Refraction
• Diffraction
• Interference
Click to see Click to see
PART D
Let’s take water waves as an example to
study the characteristics of waves….
The behavior of water waves demonstrates
all these characteristics……..
characteristics
Reflection of Waves
A travelling wave is reflected when it hits a barrier.
This phenomenon can easily be observed when a travelling water
wave hits a reflector in the ripple tank.
Reflection of Waves
Reflected
waves
Reflector
Refraction of Waves
- The speed of a water wave increases with depth. This change
in speed is accompanied by refraction.
This effect is a consequence of the wave equation, v = ƒ.
Since ƒ is constant, a decrease in v produces a decrease in .
Diffraction of Waves
When a travelling water wave hits an obstacle, the wavefronts
spreads out round the edge and becomes curved.
This phenomenon refers to diffraction.
The wavelength of the wave is not changed in diffraction.
Interference of Waves
When two or more waves propagating in the same medium meet at the
same point, interference is said to occur.
A stable interference pattern can be observed when two water
waves of same frequency meet one another in a ripple tank.
+ = Click for
example
We have seen that mechanical waves (water waves in our example)
well demonstrate these characteristics.
Electromagnetic waves show all these characteristics as well.
It is known that light demonstrates all these five characteristics of
waves, do you think that light exists in the form of wave ?
it is an electromagnetic
wave.
Think
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answer
All kinds of waves demonstrate these 5 characteristics.
Yes --
PART E
After this lecture, you should be able
to answer the following questions :
Now you have learned the basic
concepts of Waves.
Are you ready ?
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End the slide show
1. What is the difference between mechanical and electromagnetic
waves ?
2. Can you give some examples of electromagnetic waves ?
3. What is the direction of the particle motion in a transverse
wave ?
4. Is sound a transverse or longitudinal wave ?
More questions
5. Is it correct that water waves do not transmit energy from one
point to another ?
If you do not have all 5 questions answered correctly,
click here and back to part B again if necessary ---->>
1. In a wave diagram, can you identify the following terms ?
(a) wavelength
(b) amplitude.
2. Write down the wave equation.
3. What are the 5 common characteristics of waves ?
If you miss any
of this questions,
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Now we come to the conclusion of introducing waves.
You should be able to tell the nature of waves, and identify
different types of waves after this lecture.
The study of waves is important in Physics.
From the motion of water to the structure of atoms,
study of waves applies almost in every category.
THE END OF LECTURE