|
| What
is the Electromagnetic Spectrum? |
Scientists
have found that many types of wave can be arranged together
like the notes on a piano keyboard, to form a scale.
The 'low
notes' have a low frequency and a long wavelength.
The 'high
notes' have a high frequency and a short wavelength. |
|
When we say
"wave", you might think of a wave on the sea. There, it's
nice and obvious what's going on - the surface of the sea is vibrating
up and down. With a sound wave, it's the air particles that are
vibrating. So what's vibrating when an electromagnetic wave passes
by? That's not so easy. Electromagnetic waves are vibrations of
magnetic and electric fields. So they don't need air in order to
travel. They don't need anything to be there at all.
| What
do I need to know about it? |
For your GCSEs, You'll need to know:-
- The
names of the types of wave
- The
order that they're arranged
in.
- The
uses of each type of wave.
- How
each type of wave is made.
- The
dangers of each type of wave.
- All
electromagnetic waves can cross a
vacuum.
- All
electromagnetic waves travel at the speed
of light.
|
 Tips
-
The red words in this
web site are the key ones.
- Where
do the waves come from? You can almost always
get a mark for saying "stars"
- they give off the lot!
- Generally,
the higher the frequency, the more the danger.
|
|
| How
do the waves fit into the electromagnetic spectrum? |
All
of these are "electromagnetic waves".
This means that although they appear to be very different, in fact
they're all made of the same kind of vibrations - but at different
frequencies.
Use
the buttons at the top of the page to find out about the waves
| How
do I remember all this? |
Try:
Rabbits
Mate
In
Very
Unusual
eXpensive
Gardens
|
meaning:
Radio
Microwaves
Infra-Red
Visible light
Ultra-violet
X-rays
Gamma rays |
|
| What
do "wavelength" and "frequency" mean? |
Wavelength
means pretty much what it says - the length of one wave.
More
precisely, it means the distance from the peak of one wave
to the peak on the next wave.
Strictly speaking, "the distance
from any point on a wave to the same point on the next cycle of
the wave". The peaks are just handy places to measure from.
It
may be measured in:
| kilometres |
km |
1,000 metres |
| metres |
m |
Awww,
come on, you know how big a metre is! |
| centimetres |
cm |
A hundredth
of a metre. But you know this already. |
| millimetres |
mm |
1/1000th
of a metre. Those tiny lines on your ruler! |
| nanometres |
nm |
1/1000,000,000th
of a metre. Or, if you prefer, a millionth of a millimetre.
Small! |
Frequency is a word used in Maths to mean "how often something happens".
With waves, it's "how many waves per second"
It may be measured in:
| Hertz |
Hz |
1 Hz means
1 wave per second |
| kilohertz |
kHz |
1 kHz is
1,000 waves per second |
| megahertz |
MHz |
1 MHz is
1 million waves per second.
Your favourite FM radio station probably broadcasts around 100
MHz |
| gigahertz |
GHz |
1 GHz is
1,000 million waves per second. Microwaves are around a few
GHz. |
|
