Science Electromagnetic Radiation Light is one of the family of radiations called the electromagnetic spectrum. Some types of electromagnetic radiation are used to transmit information such as computer data, telephone calls and TV signals.
The electromagnetic spectrum The pattern produced when white light shines through a prism is called the visible spectrumspectrum: A series of similar waves, arranged in order of wavelength or frequency.. The prism separates the mixture of colours in white light into the different colours red, orange, yellow, Refraction from a green, indigo and violet. differe tic In fact, visible light nt radiation is only part of the types , electromagnetic of arrange spectrumelectroma electro d in gnetic spectrum: magne order of The
prism
frequency or wavelength.. It’s the part we can see.
The electromagnetic spectrum and its uses Typica Wa ength l use vel
electromradiatio Frequency agnetic n Type of gamm on cells medical highest a killing images of radiati cancer X-rays
shortest
bones
sunbeds
ultraviolet radiation visible light infrar ed
seeing radiatio n optical
microwaves radio waves
lowest e signals s
Photo ns and ionisa tion Electro magneti c radiatio n comes in tiny ‘packet s’ called photons . The photons deliver differen t quantiti
o f e n e r g y , w i t h r a d i o p h o
to ns de liv eri ng th e s m all es t a m ou nt, an d ga
mma photons deliveri ng the greates t amount of energy. If the photons have enough energy, they can break molecul es into bits called ions.
fibre communication cookin g televi sion lo ng es t
T h i s i s c a l l e d i o n i s
ati on . Th es e ty pe s of ra di ati on ar e ca lle d io
ni s T p si e h n ct e g r di u ra ff m di el er at e e ct io nt r n o ty mp In a th g e e n s el et of e ic ct s el r p e o e ct m ct a r ro g u m n ma et : g ic
n e t i c r a d i a t i o n , a r r
anged in order of frequen cy or wavele ngth. only the three types of radiatio n, which have the photons with most energy, are
ionising . These are ultravi olet, Xrays and gamma rays.
Damag ing to health higher only The ions produc ed when ionising radiatio n breaks up molecul es can
t a k e p a r t i n o t h e r c h e m i c a l r e a c t
io ns . If th es e ch e mi ca l re ac tio ns ar e in ce lls of yo ur bo dy , th e ce lls
can die or become cancero us. This is the reason that ionising radiatio n can be
damaging to
health.
Energy and intensity The intensity of electromagnetic radiation is the energy arriving each second. This depends on two things: the energy in each photon, and the number of photons arriving each second. To have the same intensity, a beam of red light would need ten times as many photons as a beam of ultraviolet, and a beam of microwaves would need a million times as many. Energy of 1 ultraviolet photon = Energy of 10 red photons = Energy of 1 000 000 microwave photons
Absorption of radiation - higher only All forms of electromagnetic radiation deliver energy. This will heat the material that absorbs the radiation. The amount of heating depends on the intensity of the radiation, and also the length of time the radiation is absorbed for.
Electromagnetic radiation An object which gives out electromagnetic radiation is called a source of radiation. Something which is affected by the radiation is a detector.
Lower intensity of radiation Further from the source, the detector receives a lower intensity
of radiation.
Intensity of beam
As the photons spread out from the source, they are more thinly spread out when they reach the detector.
Ionising radiation Ionising radiation can break molecules into smaller fragments. These charged particles are called ions. As a result, ionising radiation damages substances and materials, including those in the cells of living things. The ions themselves can take part in chemical reactions, spreading the damage. Ionising radiation includes:
ultraviolet radiation, which is found in sunlight X-rays, which are used in medical imaging machines gamma rays, which are produced by some radioactive materials Non-ionising radiation Not all types of electromagnetic radiation are ionising. Radio waves, light and microwaves are among them.
Microwaves
Microwaves are used to heat materials such as food. The
molecules in the material absorb the energy delivered by the microwaves. This makes them vibrate faster, so the material heats up. The heating effect increases if:
the intensity of the microwave beam is increased the microwave beam is directed onto the material for longer So you need to cook food for longer in a less powerful microwave oven. This is why they have power ratings, and food labels recommend different cooking times depending on this.
Transmitting information Infraredinfrared radiation: Electromagnetic radiation emitted from a hot object. light, microwavesmicrowaves: Electromagnetic radiation with a frequency between that of visible light and radio waves. and radio wavesradio waves: Low frequency electromagnetic radiation used to transmit information such as television and radio programmes. are all used to transmit information such as computer data, telephone calls and TV signals.
Infrared light Information such as computer data and telephone calls can be converted into infrared signals and transmitted by optical fibres. Optical fibres are able to carry more information than an ordinary cable of the same thickness. In addition the signals they carry do not weaken so much over long distances. Television remote controls use infrared light to transmit coded signals to the television set in order to, for example, change channels or adjust the volume.