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Transcript of ELECTROMAGNETIC SPECTRUM
Where do these waves can be use?
How do waves fit into the
HOW THEY'RE MADE?
Thursday, March 6, 2014
Vol XCIII, No. 311
INTRODUCTION TO EM Spectrum
Tour of Electromagnetic Spectrum
What is an EM spectrum?
The EM spectrum is the range of all types of EM
is the energy that travels and spreads out as it goes - the
that comes from the lamps in your house and the
that come from radio station are two types of
The other types of EM radiation that make up EM spectrum are
When we say "
", you might think of a wave on the sea.
that are vibrating.
So, what's vibrating when an
Electromagnetic Waves are vibrations of
need air in order to travel. They
need anything to be there at all.
What do you need to know about EM spectrum?
of the types of wave
that they're arranged in.
of each type of wave.
How each type of wave is
of each type of wave.
All electromagnetic waves can
cross a vacuum
All electromagnetic waves travel at the
speed of light
This means that they although they appear to be very different, in fact they're all made of the same kind of vibrations - but at
are made by various types of
, depending on the wavelength. They are also given off by
stars, sparks and lightning
, which is why you hear interferences on your radio in a thunderstorm.
Microwaves are basically extremely high frequency radio waves, andare made by various types of
, they're made by transmitter chip and an antenna, in a
they're made by a "magnetron".
Their wavelength is usually a
couple of centimeters
. Stars also give off microwaves.
Infrared waves are just below visible red light in the electromagnetic Spectrum. "
" means "
think infra-red waves as a heat, since they're given off by
, and you can feel them as warmth on your skin.
Infra-red waves are also given off by
Stars, lamps, flames
and anything else that's warm - Including
Lights waves are given off by
anything that's hot enough to glow.
This is how
work - an electric current heats the lamp filament to around 3,000 degrees, and it glows white-hot.
the surface of the
is around 5,600 degrees, and it gives off a great deal of light.
Ultra violet light is made by
for example, on
. It is given off by the Sun in large quantities. We call it "
" for short.
The photo shows a
in a chip shop.
very high frequency waves
, and carry a lot of energy. they will pass through most substances, and this makes them useful in medicine and industry to see inside things.
X-ray are given off by stars, and are strongly by some types of
works by firing a beam of electrons at a "target". If we fire the electrons with enough energy, X-rays will be produced.
Are given off by
and by some
extremely high frequency waves
, and carry a large amount of energy.
They pass through most materials, and are quite difficult to stop - you need lead or concrete in order to block them out.
The electromagnetic (EM) spectrum is the range of all types of EM
is energy that travels and spreads out as it goes – the
that comes from a lamp in your house and the
that come from a radio station are two types of electromagnetic radiation.
are the lowest frequencies in the electromagnetic spectrum, and are used mainly for
Radio waves are
, around 1~2 km in wavelength.
, around 100m in wavelength,used by other "AM" stations.
which stands for "
Very High Frequency
" and has wavelengths of around 2m. This is where you find stereo "FM" radio stations,such further up the VHF band are civilian aircraft and taxis.
stands for "
Ultra High Frequency
", and has wavelengths of less than a meter. It's used for Police radio communications, television transmissions and military aircraft radios - although military communications are now mostly digital and encrypted.
Microwaves are also used by fixed traffic
, and for
, which is used by
aircraft, ships and weather forcasters
cause water and fat molecules to vibrate, which makes the substances hot.
So we can use microwaves to
many types of food.
use microwaves, as they can be generated by a small antenna, which means that the phone doesn't need to be very big. The drawback is that, being small, they can't put out much power, and they also need a line of sight to the transmitter. This means that mobile phone companies need to have many transmitter towers if they're going to attract customers.
waves are called "IR" for short.
They are used for many tasks, for example,
for TVs and video recorders, and
use heat lamps to help heal sports injuries. IR is also used for short-range communications, for example between mobile phones, or for the Dolby Screentalk headset system used in some cinemas.
Because every object gives off IR waves, we can use them to "see in the dark".
for weapons sometimes use a sensitive IR detector.
Apart from remote controls, one of the most common modern uses for IR is in the field of security.
" (PIR) detectors are used in
systems, and to control the security lighting that many people have fitted outside their houses. These detect the Infra-Red emitted by people and animals.
Weather forecasters use satellite
pictures to see what's heading our way. Some of the images they use are taken using IR cameras, because they show cloud and rain patterns more clearly.
We use light to see things! As the
sends so much light towards our planet, we've evolved to make use of those particular wavelengths in order to sense our environment.
Light waves can also be made using a
. This works differently to a
, and produces "coherent" light.
Lasers are used in Compact Disc & DVD players, where the light is reflected from the tiny pits in the disc, and the pattern is detected and translated into sound or data.
Lasers are also used in laser
, and in
aircraft weapon aiming systems
When you mark your possessions with a
security marker pen
, the ink is invisible unless you shine a UV lamp at it.
Ultraviolet rays can be used to
. Hospitals use UV lamps to
sterilize surgical equipment
and the air in operating theaters.
Food and drug
companies also use UV lamps to sterilize their products.
Suitable doses of Ultraviolet rays cause the body to
produce vitamin D
, and this is used by doctors to treat vitamin D deficiency and some skin disorders
Uses for UV light include getting a
detecting forged bank notes
in shops, and hardening some types of
You also see
UV lamps in clubs
, where they make your clothes glow. This happens because substances in washing powder "fluoresce" when UV light strikes them - they absorb the UV and then re-radiate the energy at a longer wavelength. The lamps are sometimes called "
" because we can't see the UV coming from them.
are used by doctors to see inside people. The
are managed by a trained x-ray technician. They pass easily through soft tissues, but not so easily through bones. We send a beam of X-Rays through the patient and onto a piece of film, which goes dark where X-Rays hit it. This leaves white patches on the film where the bones were in the way.
X-Rays are also used in
airport security checks
, to see inside your luggage. They are also used by astronomers - many objects in the universe emit X-rays, which we can detect using suitable radio telescopes.
Lower energy X-Rays don't pass through tissues as easily, and can be used to scan soft areas such as the brain
Because Gamma rays
can kill living cells
, they are used to kill cancer cells without having to resort to difficult surgery.
This is called "
", and works because cancer cells can't repair themselves like healthy cells can when damaged by gamma rays. Getting the dose right is very important!
There's also targeted radiotherapy, where a radioactive substance is used to kill cancer cells - but it's a substance that'll be taken up by a specific part of the body, so the rest of the body only gets a low dose. An example would be using radioactive iodine to treat cancer in the thyroid gland.
Gamma rays kill microbes, and are used to sterilise food so that it will keep fresh for longer.
This is known as "irradiated" food.
Gamma rays are also used to sterilise medical equipment.
THE DANGERS OF EM SPECTRUM WAVES
of radio waves are believed to cause
Prolonged exposure to microwaves is known to cause "
" in your eyes, which is a clouding of the lens, preventing you from seeing clearly (if at all!) So
don't make a habit of pressing your face against
the microwave oven door to see if your food's ready!
Recent research indicates that microwaves from
can affect parts of your brain - after all, you're holding the transmitter right by your head. Other research is inconclusive, although there is a feeling that you're more
and your brain is still growing.
The danger to people from too much Infra-Red radiation is very simple -
Too much light can
damage the retina
in your eye.
This can happen when you look at something very bright, such as the Sun.
Although the damage can heal, if it's too bad it'll be permanent.
Ultra Violet Light
Large doses of UV can
the retina in your eyes, so it's important to check that your sunglasses will block UV light.
Large doses of UV cause
and even skin cancer. Fortunately, the ozone layer in the Earth's atmosphere screens us from most of the UV given off by the Sun. Think of a
as a radiation burn!
X-Rays can cause
cell damage and cancers
This is why Radiographers in hospitals stand behind a shield when they X-ray their patients. Although the dose is not enough to put the patient at risk, they take many images each day and could quickly build up a dangerous dose themselves.
Gamma rays cause
and can cause a variety of
in growing tissues, so unborn babies are especially vulnerable.
Roldan, Lean Dennis
Natsci 4 (Physics)