Introduction Introduction

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The basicsPart A : Definition - Definition of Vibration and waves. - Basic Properties of waves. - Terminology of waves.

Part B : Types of Waves and Terminology. - Mechanical waves : - Transverse and Longitudinal waves.

Part C : The Wave Equation.Part D : Common Characteristic of WavePart E : Revision

PART APART A10.110.1 What are waves? page232

DDefinition efinition A periodic disturbance which travels through a

medium from one point in space to the others.

OR A wiggle in space and time is a wave.

What carries waves? A medium, a medium is the material through which a wave travels. A medium can be a gas, liquid, or solid.

What causes waves?Waves are created when a source of energy causes a medium to vibrate.

PART APART ADefinition of VibrationDefinition of Vibration

A vibration is a repeated back and forth, up and down, from side to side, to and fro, in and out motion in time. OR

A wiggle in time.

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….

Amplitude(A) Definition:

The amplitude is the distance from the midpoint to the crest (or to the trough) of the wave.

Wavelength (λ)Definition:

The wavelength is the distance from the top of one crest to the top of the next one.

ORThe distance between successive identical parts of the wave.

ORThe distance from successive crest to crest or trough to trough

Unit: meters

Frequency(f)Definition:

The frequency is the number of to and fro vibrations per second.

One vibration per second is 1Hz; two vibrations per second is 2 Hz, and so on.

Unit: Hertz (Hz) defined to be one cycle / wave per sec.

Higher frequencies are measured in kilohertz(kHz), and still higher frequencies in megahertz(MHz).

Time period(T)Definition:

The period (T) of a wave or vibration is the is the time it takes for a complete vibration --- for a complete cycle.

It is related to frequency by

T = 1/ƒ Unit : s

Definition: The wave velocity is the displacement traveled by the wave in one second ……....

The speed of periodic wave motion (v) is related to the frequency and wavelength of the waves by --

Wave speed = wavelength/ periodWave speed= wavelength x frequency

Wave speed = wavelength/ periodWave speed= wavelength x frequency

The Wave Equation

PART CPART C

Click to explore

10.2 Wave Speed page233

v = ƒv = ƒ

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

Longitudinal Longitudinal WavesWaves

Transverse Transverse WavesWaves

TYPES OF WAVESTYPES OF WAVESWaves Waves are classified into two different types according to their natures, how they move means their direction of vibration :

10.3 Transverse WavesTransverse Waves page234page234

Water waves, pulse in a stretched string.

Examples

Definition: A wave in which the medium vibrates in a direction perpendicular (transverse) to the direction in which the wave travels. (page 249)

10.3 Longitudinal WavesLongitudinal Waves page 234page 234

A wave in which the medium vibrates in a direction parallel (longitudinal) to the direction in which the wave travels.

ExamplesSound, or a spring oscillating up and down, etc.

10.4 Sound Waves page235Sound is the propagation of vibrations through a

material medium--- a solid, a liquid or a gas.

Molecules in the air vibrate about some average position creating the compressions and rarefactions.

Sound cannot travel in a vacuum (no medium).

We call the frequency of sound the pitch.

Speed of Sound Depends on the material of the

vibrating medium Sound can vibrate water, wood

(speaker enclosures, pianos), metal, plastic, etc.

Sound speed in dry air is 330 meters/second at 0o C

Faster in warm air, slower in cold Water 4 times faster, steel 15

times faster The human ear can normally hear

pitches from sound ranging from about 20Hz to about 20,000Hz.

Sound waves of frequencies lower than 20Hz are called infrasonic waves.

Sound waves of frequencies higher than 20,000Hz are called ultrasonic waves.

After this lecture, you should be ableto answer the following questions :

Now you have learned the basicconcepts of WavesWaves.

Are you ready ?

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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.

If you miss any of this questions,

go back to the lessonby clicking this

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Now we come to the conclusion of introducing waves.

You should be able to tell the nature of waves, and identifydifferent 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 LECTURETHE END OF LECTURE

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 ves L o ng itud ina l w a ves

Mechanical w aves

T ra ns ve rs e w a ves

Elec tromagnetic w aves

WA V E S

1. Mechanical WavesA material medium is necessary for the

transmission for mechanical waves. Mechanical waves cannot travel through vacuum.

Click forexamples

Water waves,

Sound

Vibration of spring