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The visible spectrum of light is only a small part of a much larger spectrum containing many other wavelengths which we can't see. This spectrum is called the ELECTROMAGNETIC SPECTRUM!

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All Electromagnetic Waves have these properties:

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All Electromagnetic Waves have these properties:

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1- They are all transverse (electromagnetic waves)
2- They can all travel through a vacuum
3- They all travel at the same speed (3 x 108 m/s) in vacuum (and air)

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Electromagnetic waves have these properties in common with all types of waves:

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Electromagnetic waves have these properties in common with all types of waves:

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1- They all move energy from one place to another
2- They can be reflected and refracted
3- They all obey the wave equation (see below)

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Though we can't physically see with our eyes the full scale of the spectrum, we know how it's wavelengths go from long to short, frequency low to high and energy low to high. (left to right)

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To remember the order of the colours in the visible part of the spectrum you can use this memory aid:
Rats and                                    Radio
Mice                                           Micro
In                                             Infrared
Venice                                      Visible
Use                                    Ultra-violet
Xtra                                            X-rays
Gondolas                               Gamma

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Uses:

They kill living cells and so are used to kill cancerous growths - Radiotherapy

Used in the sterilisation of medical equipment

In the food industry, fresh fruit is treated with gamma rays to prolong its shelf life

Dangers:

Gamma rays can cause cancer

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Uses:

Medical Diagnosis - X-ray photographs to identify broken bones

Medial Therapy - The shortest wavelength X-rays are the most penetrating and they can be used to kill cancer cells

Dangers:

X-rays can damage cells and cause cancer

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Uses:

To identify forgeries of bank notes

UV rays can be used for skin treatments in hospital

UV rays kill bacteria _ UV lamps used in kitchens to sterilise crockery and in water chillers

Dangers:

Exposure to large amounts of UV radiation can damage eyes and cause skin cancer (minimised by using high SPF sunscreen and reducing time in sun)

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They have the longest wavelength in the E-M spectrum.
Range: a few cm to several km
Uses:

Transmission of TV programmes

Transmission of local radio programmes, police ad ambulance messages etc.

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Uses:

Fast food cooking - microwaves pass easily through food and are absorbed by water molecules.

Radar - Detects positions of ships, aircraft or missiles (travels faster than ultrasound)

Satellite communication eg GPS

Dangers:

Since our bodies contain a large volume of water if exposed to  a large dose of microwaves, internal organs could be damaged as water in our cells is heated up.

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All hot objects emit infra-red (I-R). The higher the temperature of an object, the more I-R it emits.
Uses:

Heating - Toaster, grills and cookers

Remote control for TV

Burglar alarms go off when they detect I-R

Night vision equipment uses I-R to detect the radiation given off by living creatures or engines

Astronomers use I-R photos to obtain information about the temperature of stars

Dangers:

Too much I-R can damage cells and result in burns.

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Uses:

Vision and photography

Optical fibre communication systems

Photosynthesis - occurs in green plants, where light energy is converted into chemical energy