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 ...

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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

Click for

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