4.1 – PROPERTIES OF WAVES

4.1 – Features of a Wave

To study optics, some starting vocabulary is neededWave

A disturbance or movement that transfers energy through matter or space, without causing any permanent displacement

EnergyThe capacity to apply a force over a distance, or

the ability to perform workForce

A push or a pull on an object

The dotted line represents the equilibrium or rest positionRemember from

section 1.3An equilibrium is a

balance in a system between opposing forces or quantities, like concentration of height

4.1 – Features of a Wave

Notice the new terms:Crest

The highest point in a wave

TroughThe lowest point in a

wave

4.1 – Features of a Wave

One of the most important properties of waves is its amplitudeAmplitude

The height of a crest or the depth of a trough, measured from the equilibrium position

4.1 – Features of a Wave

Another important property of waves is its wavelengthWavelength

The distance from one crest to the next, or one trough to the next

Also the distance to complete one crest and one trough

4.1 – Features of a Wave

Another important property of waves is its frequencyFrequency

The number of repetitive motions that occur in a given time

4.1 – Features of a Wave

AmplitudeThe units of amplitude depend on what kind

of wave it isSound decibels (dB)Light volts per meter (V/m)

WavelengthMeasured in metres (millimetres,

micrometres, etc.)Frequency

Measured in:Hertz (Hz)

The number of cycles per second

4.1 – Features of a Wave

Frequency and wavelength have an inverse relationshipInverse relationship (inversely proportional)

When one value increases as the other decreases As the wavelength increases, the frequency

decreases

4.1 – Features of a Wave

4.1 – Features of a WaveFrequency, wavelength and amplitude

relate to properties we recognizeFrequency and wavelength

The colour of visible light Red 400 – 484 THz Blue 668 – 789 THz

The pitch of sound C4 (middle C) 261.6 Hz C5 523.3 Hz

4.1 – Features of a WaveFrequency, wavelength and amplitude

relate to properties we recognizeAmplitude

A higher amplitude means the wave carries more energy How bright a light is

The higher the amplitude, the brighter the light

The volume of sound Softest sound you can hear 0 dB Breathing 10 dB Typical library 40 dB Typical conversation 50 – 60 dB Busy street 90 dB Typical concert 120 – 150 dB Eardrum rupture >175 dB

Most types of waves require something to travel throughMedium

The matter (a solid, liquid, gas or combination of these) that a wave travels through Sound waves medium is air Ocean waves medium is water

Not all waves require a mediumLight travels the fastest through a vacuum

Different types of waves interact differently with a medium (section 4.2)Sound speeds up as the medium gets denserLight slows down as the medium gets denser

4.1 – Two Types of Waves

4.1 – Two Types of Waves

Cherenkov radiationWhen light travels

through water, it does so at 75% of its maximum speed

Electrons in the water can therefore travel faster than the slowed-down light, producing this blue glow

Type 1Transverse wave

A wave in which the matter of the medium moves up and down, at 90 degrees to the direction of wave travel

ExamplesFlicking a rope up and down Light waves“The Wave”

Think about it – the wave moves left or right, but you move up and down

4.1 – Two Types of Waves

4.1 – Two Types of Waves

Type 2Compression wave

A wave in which the medium moves back and forth along the same direction that the wave travels

ExampleSound

Air compresses and expands, pushing sound energy through the air

4.1 – Two Types of Waves

Earthquakes feature both types of wavesP waves (primary waves)

Compression wavesCan travel through any mediumTravel the fastest, so they arrive first

S waves (secondary waves)Transverse wavesCan only travel through solidsTravel slower than P waves, so they arrive

second

Pg 142 – Active Noise Cancellation

Multiple waves can overlapWhen they do, their amplitudes add together

Amplitudes above the equilibrium are positiveAmplitudes below the equilibrium are negative

We can use thisNoise cancelling headphones have a

microphone and a signal processorThe microphone measures the background noiseThe signal processor analyzes the signal and

identifies the positive sound wave The sound that is heard, but will be blocked

Pg 142 – Active Noise CancellationThe headphone speakers then produce

another sound wave that has the complete opposite shape of the positive waveThis is called the negative wave

The positive and the negative waves cancel each other out

4.1 – Properties of Waves

Homework break #1Reading Check

Pg 138, #1-5

4.1 – PROPERTIES OF WAVES