Download EM Waves Summary Sheet File

Pupils should:
 Know that the family of Electromagnetic waves consists of:

Radio, Microwaves, Infrared, Visible Light, Ultraviolet, X-rays and Gamma Rays.
 Be able to describe the properties of all EM Waves:
 EM waves can travel through a vacuum; they do not need a material in which to travel.
 All EM waves travel at the same speed in vacuum i.e. 300,000,000 metres per second.
 EM waves change speed when they travel through a material i.e. light and infrared waves
slow down when they enter a dense material such as glass.
 The energy of an EM wave depends upon its frequency. The higher the frequency the greater
the energy of the wave.
Radio waves have the lowest frequency and therefore the least energy.
Gamma rays have the highest frequency and therefore the most energy.
 Know the uses of the following relatively low energy waves:
 Microwaves – Microwaves like radio waves are used in many types of communication such
as mobile phone technology, line of sight relay stations and satellite communication. Water
tends to absorb microwaves and can convert the microwave energy into heat energy (This is
the principle of the microwave oven).
 Infrared waves – Hot objects emit IR waves. They are also used in communication. Infrared
lasers shine these waves down fibre optic cables.
 Visible light – Light can also be used for communication purposes for example, CD and
DVD players use lasers to read the information contained on the discs.
 Know the uses of the following relatively high energy ionising radiation waves:

Ultraviolet – UV can burn the skin possibly resulting in skin cancers. They can be used to
cause materials to fluoresce and give off visible light.

X-Ray – X-rays have enough energy to penetrate soft tissue such as skin, muscle, fat and
connective tissue but they are absorbed by denser material such as bone. They are therefore
useful for taking pictures of the skeleton. However, these high-energy rays can damage or
even kill cells when a person is overexposed to them.

Gamma Rays – Gamma rays are extremely dangerous EM waves, they are highly
penetrating and they can also damage and kill cells if overexposed. However, if they are
used carefully they can be used to kill cancerous cells in the human body.
Ionising radiation like UV, X-rays and Gamma rays are very dangerous to us and should be
treated with caution, but they can be very useful to us when used in both medical and
industrial applications.
 Know that mirrors and other flat surfaces can reflect EM waves.
Angle of incidence = Angle of Reflection
 Know that EM waves can be refracted.
 When a ray enters a denser material it slows down and can refract towards the normal
to the surface.
 When a ray enters a less dense material it speeds up and can refract away the normal
to the surface.
 Know and explain that Total internal reflection occurs when a ray’s angle of incidence, within a
dense material, is greater than the critical angle. (Higher tier only)
 Know and explain that a ray can be trapped within a long optical fibre if it always strikes the
boundary at an angle greater than the critical angle. (Higher tier only)
 Use the wave equations:
V=fxλ
s=d
t
 Describe how Microwaves and Infrared can be used to transmit signals over long distance, including:
 Mobile phone communication (Microwaves)
 Geostationary (geosynchronous) satellite communication (Microwaves)
 Intercontinental optical fibre links (Infrared)
Pupils should consider the following when describing communication networks:
reliability of transmission of signals, time delays due to the long distances involved,
investment required to set up a network and flexibility of use (mobile satellite
communication used by news reporters compared to fixed installations required for
optical fibre transmissions)
 Discuss the claimed health risks associated with Mobile phone transmitters and Tetra masts.
 High power transmitters emit very intense electric and magnetic fields.
 This could be potentially dangerous to residents close to a transmitter.
 Lots of anecdotal evidence to suggest it is a real threat, which cause dizziness, nausea and
even certain types of cancer.
 No hard scientific evidence to show the link between the intense field and the claimed health
problems. However, it should be considered investigators might not be totally impartial!