Introduction to Waves Auto slide change for this page, WAIT…..

Introduction to WavesIntroduction to Waves

Auto slide change for this page, WAIT…..

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 APART A

Definition of waveDefinition 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 wavesBasic 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 BPART B TYPES OF WAVESTYPES OF WAVESWaves Waves are classified into different types according to their natures :

T ra ns ve rs e w a ve s L o ng itud ina l w a ve s

Mechanical w aves

T ra ns ve rs e w a ve s

Elec tromagnetic w aves

WA V E S

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.

clickAnd ...

Click forexamples

Water waves, sound, vibration of spring, etc.

1.1 Transverse WavesTransverse 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 WavesLongitudinal Waves

• A wave in which the motions of the matter particles are in the same direction as the wave propagation.

ExamplesSound, 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 EquationThe Wave EquationThe wave velocity is the displacement traveled by the wave in one second ……....

The wave velocity (v) is related to frequency and wavelength by --

v = ƒv = ƒThe Wave Equation

PART CPART C

Click to explore

Using the Wave EquationUsing the Wave EquationExample :

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 ofContents

By using the wave

equation, v = ƒ 3.0 = ƒ(0.6) i.e ƒ = 5.0 Hz

• Transmission of energyTransmission of energy• ReflectionReflection• RefractionRefraction• DiffractionDiffraction• Interference Interference

Click to see Click to see

PART DPART 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 WavesReflection of Waves

A travelling wave is reflectedreflected when it hits a barrier.

This phenomenon can easily be observed when a travelling waterwave hits a reflector in the ripple tank.

Reflection of WavesReflection of Waves

Reflectedwaves

Reflectedwaves

Reflector

Refraction of WavesRefraction of Waves

- The speed of a water wave increases with depth. This change in speed is accompanied by refraction 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 WavesDiffraction 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 WavesInterference of WavesWhen two or more waves propagating in the same medium meet at the same point, interference 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

Effects of Interference