2. Electromagnetic Spectrum
 A continuous spectrum of waves.
 Includes the visible spectrum.
 All waves have the following properties:
 they all transfer energy
 they are all transverse waves
 they all travel at the speed of light (300 000 000 m/s)
 they can all be reflected, refracted and diffracted.
 Wavelengths vary continuously from one end of the
spectrum to the other.

4. Different waves
 Radio waves
 Longest wavelength
 Used by long- , medium- and short-wave radio
 Microwaves
 Used for cooking food, communications and radar
 Infra-red (IR)
 Emitted by all objects; (hotter = more IR)
 Used for heat sensitive cameras, remote controls etc
 Can be harmful if in large doses

5. Different waves
 Visible light
 Visible to the human eye
 Ultraviolet light
 Harmful to human eyes and can damage the skin
 Causes certain chemicals to fluoresce: used as
security marker
 X-rays
 Used to take radiographs in medicine and at airports
for security checks
 Overexposure can cause cancer

6. Different waves
 Gamma rays
 Highly penetrating: can cause
damage to living cells
 Used to sterilise medical
instruments and kill micro-
organisms in food, (keeps it
fresher longer)
 Used to treat cancer in
radiotherapy

7. Communication
Digital Signals Analogue signals
 Uses a sequence of  Electrical voltages or
numbers, (1 and 0) currents that vary
 Called Binary Code continuously
 Electrical impulses sent  Will often require an
down telephone lines amplifier

8. Communication
 There are several advantages in using digital
transmission:
 All signals weaken and need to be amplified.
 Amplified digital signals create clean accurate copies
of the original
 When analogue signals are amplified, accompanying
noise is also amplified: the signal can get “cluttered”