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.
wavelength piano analogy
Caution: don't get too hung up on this keyboard idea - sound waves are NOT part of the electromagnetic spectrum

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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?

Wavelength from ~ 1m to ~ 1km Wavelength around a few cm Wavelength around 0.01 mm Wavelength 400 to 700 nm Wavelength around 1 nm Wavelength around 0.01 nm Wavelength around 100 nm

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.

 

Created by Andy Darvill for GCSE Physics
Main site: www.darvill.clara.net

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