WAVES IN ACTION
The Electromagnetic
Spectrum
What Is The Electromagnetic Spectrum?
• We are all familiar with LIGHT• Light is part of the EM spectrum –
it is an electromagnetic wave.• There are several different types of
EM waves.• The EM spectrum is a way of
classifying all the types of waves according to wavelength
What are Electromagnetic Waves?
• Electromagnetic waves are just like any other wave, with one exception:
• They are the only type of wave that can travel through a vacuum
• They are transverse waves• They all travel at the same speed:
300,000,000 m/s (3x108 m/s)
The Electromagnetic Spectrum
Radio Waves
• Created by oscillations (vibrations) of electrons in a conductor.
• Very long wavelength (few km to few cm) – low frequency – so low energy waves.
• Used to transmit radio and TV signals.• Travel in straight lines, but can be
bounced off the upper atmosphere, so can travel around the world.
The Electromagnetic Spectrum
MICROWAVES
• Wavelength from cm to .0001 m• Used for cooking food• Microwaves make water molecules
vibrate, which causes food to get very hot very quickly.
• Penetrate only a few cm, the heat is then carried inside by conduction
MICROWAVES
• Microwaves are also used for communication.
• Mobile telephones use microwaves.• They are also used to communicate
with satellites as they can pass through the upper atmosphere
• They also do not spread out much, so they are easy to use with a dish.
The Electromagnetic Spectrum
INFRA-RED
• Wavelength from mm to 0.000001m.• Most familiar use is for cooking and
heating, like electric grills and heaters.
• Infra red waves are easily absorbed at the surface of things, making them hot, then heat is carried inside by conduction.
INFRA-RED
• Everything gives out Infra-red• This allows cameras to use IR instead
of visible light for night-vision.• They are also used for thermo-
imaging cameras, to find people buried in earthquakes. They will be being used in New York.
• They are also used for remote controls
The Electromagnetic Spectrum
VISIBLE LIGHT
• This is the EM wave we are most familiar with.
• Different colours have different wavelengths, from red (longest) to violet (shortest).
THE VISIBLE SPECTRUM
RED ORANGE YELLOW GREEN
BLUE INDIGO VIOLET
The full spectrum is:
These can be remembered using:Richard Of York Gave Battle In Vain!
The Electromagnetic Spectrum
ULTRA VIOLET
• Shorter wavelength – 0.000001m to 0.000000001m, frequency higher.
• Carry more energy, and can penetrate top layers of skin, damaging the lower layers
• This can cause sun burn, and possibly skin cancer of a long period of time.
• The eyes are very sensitive to UV, so sunglasses should always be worn in bright sunshine.
• Most UV radiation from the sun is filtered by the ozone layer.
Ultra Violet
• UV can be used to sterilise things, as bacteria can be killed by UV.
• UV is also used for anti-counterfeit purposes in bank notes.
• UV tubes are used in entertainment venues – they make white clothes glow
The Electromagnetic Spectrum
X-RAYS
• Discovered accidentally by Wilheim Röntgen in 1895
• Very short wavelength (0.00000001m to 0.000000000001m) – so a very high frequency.
• Very energetic – can pass through your body.• Produced by firing electrons at a metal target
X-Rays
• Their ability to pass through soft tissue, but not bone, makes them very useful in medicine.
• They are completely stopped by metals, making them useful for security scanning at airports.
X-Rays
• Because they carry a lot of energy they can easily damage or kill cells.
• This can lead to cancer if over-exposure occurs.• Very small amounts are used in hospitals and are
relatively safe, however the operator will stand behind a lead screen to stop unnecessary exposure
• X-rays are also used to treat cancer by killing cancerous cells.
The Electromagnetic Spectrum
GAMMA RAYS
• Extremely short wavelength (0.0000000001 to 0.000000000000001 m)
• Extremely high frequency, so carry a large amount of energy.
• Gamma rays arise from the nuclei of unstable atoms.
GAMMA RAYS
• Very harmful to living things – they can easily kill or damage cells leading to cancer.
• They are used to sterilise hospital equipment as bacteria are killed instantly on exposure
• They can also be used to kill bacteria in food. This is known as irradiation.
GAMMA RAYS
• A very important application of gamma rays is the treatment of cancer.
• More effective than X-rays because they carry more energy.
• Careful focussing of gamma rays avoids damage to healthy cells.
Tracers
• Particles which give out gamma rays can be used for “tracers”.
• A small amount of radioactive material is injected into the patient
• The movement of radiation can be monitored from outside the body.
• This allows doctors to pick up problems, such as poor blood circulation, as well as detecting tumours.
RISKS and BENEFITS
• X-Rays and Gamma rays are both used in medicine.
• Their benefits are they destroy cancer, and avoid surgery, as well as use for diagnostic purposes.
• They can also cause cancer, and may cause sickness if exposures are too large.
THE COMPLETE ELECTROMAGNETIC SPECTRUM
Long ShortWAVELENGTH
FREQUENCYLow High
ENERGYLow High
IMPORTANT NOTES
I. All EM waves travel at the same speed
II. Different parts of the EM spectrum have different properties
III. The higher the frequency of EM radiation, the higher the energy it carries.
