Wave Model of Wave Model of Radiation RevisionRadiation Revision

WavesWaves

Waves are disturbances that transfer Waves are disturbances that transfer energy in the direction of the wave energy in the direction of the wave without transferring matter.without transferring matter.

The frequency is the number of waves The frequency is the number of waves per second.per second.

Wavelength is the distance between the Wavelength is the distance between the same point on 2 adjacent disturbances.same point on 2 adjacent disturbances.

Amplitude is the distance between the Amplitude is the distance between the crest or trough and the undisturbed crest or trough and the undisturbed position.position.

Speed = frequency x wavelength.Speed = frequency x wavelength.

Longitudinal and Longitudinal and Transverse WavesTransverse Waves Longitudinal WaveLongitudinal Wave

– Particles vibrate in same direction Particles vibrate in same direction that the wave moves.that the wave moves.

Transverse Wave Transverse Wave – Particles vibrate at 90 degrees to Particles vibrate at 90 degrees to

the direction that the wave moves.the direction that the wave moves.

Wave DiagramsWave Diagrams

Waves in water can be shown Waves in water can be shown using diagrams.using diagrams.

ReflectionReflection

Ripples can also bounce off a barrier, and they can be made to change direction.

RefractionRefraction

When waves enter a different When waves enter a different depth they change speed – and depth they change speed – and direction.direction.

Light as a waveLight as a wave

Because light acts in a similar Because light acts in a similar way to water it is considered a way to water it is considered a wave also.wave also.

Light can be reflected and Light can be reflected and refracted also.refracted also.

Diagrams for light waves are Diagrams for light waves are different.different.

The Electromagnetic The Electromagnetic SpectrumSpectrum All types of EM waves travel at the All types of EM waves travel at the

same speed.same speed. EM waves can travel through a EM waves can travel through a

vacuum unlike sound waves.vacuum unlike sound waves. Different colours have different Different colours have different

wavelengths and frequencies.wavelengths and frequencies. Different wavelengths have different Different wavelengths have different

uses due to their differences in uses due to their differences in reflection, absorption and transmission reflection, absorption and transmission by different materials.by different materials.

The EM SpectrumThe EM Spectrum

Uses of EM RadiationUses of EM Radiation

Gamma and X rays penetrate human Gamma and X rays penetrate human flesh and are used for medical purposes.flesh and are used for medical purposes.

Microwaves penetrate the atmosphere Microwaves penetrate the atmosphere and are used for mobiles and other and are used for mobiles and other devices that use satellites.devices that use satellites.

Satellite dishes and microwave ovens Satellite dishes and microwave ovens are made of metal because they reflect are made of metal because they reflect microwaves.microwaves.

Radiowaves do not penetrate the Radiowaves do not penetrate the atmosphere as well but can be reflected atmosphere as well but can be reflected off the ionosphere over long distances.off the ionosphere over long distances.

Amplitude and Amplitude and Frequency ModulationFrequency Modulation Waves can carry information by Waves can carry information by

varying in amplitude or frequency.varying in amplitude or frequency. Because the signal various the same Because the signal various the same

way as the information, it is called way as the information, it is called analogue.analogue.

When the radio waves meet a metal When the radio waves meet a metal aerial they produce electrical waves aerial they produce electrical waves which enter the receiver.which enter the receiver.

The receiver reproduces the original The receiver reproduces the original signal from the pattern of variation.signal from the pattern of variation.

AM and FM ModulationAM and FM Modulation

Digital SignalsDigital Signals

Signals can be carried by IR or light waves Signals can be carried by IR or light waves through optical fibres.through optical fibres.

Other information can be transmitted Other information can be transmitted digitally.digitally.

Sound is converted to a digital signal made Sound is converted to a digital signal made from 0s and 1s.from 0s and 1s.

The coded information controls the bursts of The coded information controls the bursts of waves (pulses).waves (pulses).

0 = no pulse, 1= pulse.0 = no pulse, 1= pulse. When the waves are received the pulses are When the waves are received the pulses are

decoded to produce the original information.decoded to produce the original information.

Digital QualityDigital Quality

Radio signals become weaker as they Radio signals become weaker as they travel and pick up random signals travel and pick up random signals called noise.called noise.

Amplification also amplifies the noise Amplification also amplifies the noise so the quality deteriorates.so the quality deteriorates.

Digital signals are not as affected by Digital signals are not as affected by noise as they are either on or off.noise as they are either on or off.

Digital signals therefore maintain their Digital signals therefore maintain their quality.quality.

Digital RadioDigital Radio