# Electromagnetic spectrum facts.

## Electromagnetic spectrum facts

• Waves carry vibrations through a medium.
• They transfer the energy locked up in the vibrations.
• Waves have a measurable speed, wavelength and frequency.
• Waves meeting a boundary between mediums may be reflected, refracted or absorbed - often a mixture of all three.
• Waves passing through a gap may be diffracted (spread) - the spreading is only noticeable if the gap is similar to the wavelength.
• Electromagnetic waves carry transverse vibrations in electrical and magnetic fields, not vibrating particles.
• E-m waves don't need matter to travel through - they can travel through empty space (a vacuum).
• In a vacuum, all e-m waves travel at (approximately) 300 million metres per second (3 x 108m/s) - the fastest speed in the universe.
• When e-m waves travel through matter (for example, light through air or glass), they travel a bit slower than this but rarely less than half as fast as in vacuum.
• Waves of different frequencies travel at different speeds in transparent matter - so a mixture of waves can be separated out by diffraction. For example, white light is split up into a mixture of colours when it goes through a prism.

## The electromagnetic spectrum table

This table is nearly all you need to know about the e-m spectrum on one page.

The electromagnetic spectrum

Print or copy it out if you want a permanent summary.

Check your syllabus to see if there are particular examples or applications you need to know about in detail. This summary should give you some useful background ideas and information.

## Amplitude, Wavelength, Frequency, and Speed

The amplitude (a) is the total distance betweeen the crest of a wave and the centre line. It's a distance, so can be measured in metres, centimetres, millimetres or ...