ScienceElectromagnetic Radiation

Light is one of the family of radiations called theelectromagnetic spectrum. Some types of electromagneticradiation are used to transmit information such as computerdata, telephone calls and TV signals.

The electromagnetic spectrumThe pattern produced when whitelight shines through a prism is calledthe visible spectrumspectrum: Aseries of similar waves, arranged inorder of wavelength or frequency..

The prism separates the mixture ofcolours in white light into thedifferent colours red, orange, yellow,green, indigo and violet. Refraction from a prism

In fact, visible light is only part of theelectromagnetic spectrumelectromagneti

c spectrum: Thedifferent types of

electromagnetic radiation, arranged in order of

frequency or wavelength.. It’s the part we can see.

The electromagnetic spectrum and its uses

Frequency Type of

electromagnet

icradiati

onTypical use

Wavel

ength

highest gamma radiation killing cancer

cells

X-raysmedicalimages of

shortest

bones

ultravioletradiation

visible light

sunbeds

seeing

infrared radiation

optical fibre

communication

microwa ves cooking

lowest radio waves

television longestsignals

Photons and ionisationElectromagnetic radiation comes in tiny ‘packets’ called photons.

The photons deliver different quantities of energy, with radiophotons delivering the smallest amount, and gamma

photonsdelivering the greatest amount of

energy.

If the photons have enough energy, they can break moleculesinto bits called ions. This is called

ionisation. These types ofradiation are called ionising radiation.

In the electromagnetic spectrumelectromagnetic spectrum:The different types of electromagnetic radiation, arranged inorder of frequency or wavelengt

h. only the three types ofradiation, which ha

ve the photons with most energy, are ionising.These are ultraviolet, X-rays and gamm

a rays.

Damaging to health - higher o

nlyT

h

e

i

o

n

s

p

r

o

d

u

c

e

d

w

h

e

n

i

o

ni

si

n

g

r

a

di

a

ti

o

n

b

r

e

a

k

s

u

p

m

ol

e

c

u

l

e

scan take part in other

chemical reactions. If these chemicalreactions are in cells of your body, the cells can die or becomecancerous. This is the reason that ionising radiation can bedamaging to health.

Energy and intensityThe intensity of electromagnetic radiation is the energy arrivingeach second. This depends on two things: the energy in eachphoton, and the number of photons arriving each second.

To have the same intensity, a beam of red light would need tentimes as many photons as a beam of ultraviolet, and a beam ofmicrowaves would need a million times as many.

Energy of 1 ultraviolet photon = Energy of 10 redphotons = Energy of 1 000 000 microwave photons

Absorption of radiation - higher onlyAll forms of electromagnetic radiation deliver energy. This willheat the material that absorbs the radiation. The amount ofheating depends on the intensity of the radiation, and also thelength of time the radiation is absorbed for.

Electromagnetic radiationAn object which gives out electromagnetic radiation is called asource of radiation.

Something which is affected by the radiation is a detector.

Lower intensity of radiationFurther from the source, the detector receives a lower intensityof radiation.

Intensity of beam

As the photons spread out from the source, they are more thinlyspread out when they reach the detector.

Ionising radiationIonising radiation can break molecules into smaller fragments.These charged particles are called ions. As a result, ionisingradiation damages substances and materials, including those inthe cells of living things. The ions themselves can take part inchemical reactions, spreading the damage.

Ionising radiation includes:

ultraviolet radiation, which is found in sunlightX-rays, which are used in medical imaging machinesgamma rays, which are produced by some radioactivematerials

Non-ionising radiationNot all types of electromagnetic radiation are ionising. Radiowaves, light and microwaves are among them.

MicrowavesMicrowaves are used to heat materials such as food. The

molecules in the material absorb the energy delivered by themicrowaves. This makes them vibrate faster, so the materialheats up.

The heating effect increases if:

the intensity of the microwave beam is increasedthe microwave beam is directed onto the material forlonger

So you need to cook food for longer in a less powerfulmicrowave oven. This is why they have power ratings, and foodlabels recommend different cooking times depending on this.

Transmitting informationInfraredinfrared radiation: Electromagnetic radiation emittedfrom a hot object. light, microwavesmicrowaves:Electromagnetic radiation with a frequency between that ofvisible light and radio waves. and radio wavesradio waves: Lowfrequency electromagnetic radiation used to transmit informationsuch as television and radio programmes. are all used totransmit information such as computer data, telephone calls andTV signals.

Infrared lightInformation such as computer data and telephone calls can beconverted into infrared signals and transmitted by optical fibres.Optical fibres are able to carry more information than an ordinarycable of the same thickness. In addition the signals they carry donot weaken so much over long distances. Television remotecontrols use infrared light to transmit coded signals to thetelevision set in order to, for example, change channels or adjustthe volume.

Microwaves

Microwave radiation can be used totransmit signals such as mobilephone calls. Microwave transmittersand receivers on buildings andmasts communicate with the mobiletelephones which are in their range.

Certain microwave radiationwavelengths pass through theEarth’s atmosphere and can beused to transmit information to and

Mobile phone base station from satellites in orbit.

Radio wavesRadio waves are used to

transmit television and

radioprogrammes. Longer wavelength radio waves are reflected froman electrically charged layer of the upper atmosphere. Thismeans they can reach receivers that are not in the line of sightbecause of the curvature of the Earth’s surface.

Microwaves and radio waves in the atmosphere

Now try a Test Bite - foundation.

Now try a Test Bite - higher.

Back to Revision Bite