distance = speed x time d = v t
Speed of sound
340 m/s
Speed of light
300,000,000 m/s
transmitter
sends signals
receiver
replays signals
microphone energy change
microphone Sound electrical
loudspeaker energy change
loudspeaker electrical sound
frequency Number of waves per second
Amplitude Wavelength
High frequency
Low frequency
High amplitude
Low amplitude
wave speed v
speed = frequency x wavelength v = f
Radio waves Same speed as light
Aerial Detects radio waves
Tuner Selects one frequency
Decoder Separates the audio signal from the carrier wave
Amplifier Increases amplitude of signal
Electricity supply Provides energy to amplifier
Loudspeaker Changes electrical signal to sound
Radio Transmission Radio frequency wave combined with audio frequency wave
Radio Transmission This is called amplitude modulaton
Amplitude modulation audio radioa.m.
Diffraction Bending round obstacles
Diffraction Long wavelength, low frequency bends more than short wavelength, high frequency
Television aerial decoder (vision) tuner amplifier TV tube decoder (sound) amplifier Loudspeaker
Television Line build-up moving backwards and forwards Lines made by electron beam across screen The lines build up to make picture
Television Brightness variation Dark areas – few electrons Light areas – many electrons
Television Image retention Eye retains image for short time 25 pictures per second – pictures seen as moving smoothly
Colour television Three electron guns One to hit red dots One to hit blue dots One to hit green dots
Colour television Colour mixing Red + Blue = Magenta Blue + Green = Cyan Green + Red = Yellow Blue+Green+Red = White
Colour television Colour mixing red blue green yellowcyan white magenta
Reflection Angle of incidence i r i = r mirror Angle of reflection =
Refraction airglass
Total Internal Reflection ir Above a certain angle (the critical angle), the light is reflected.
Optical Fibres i Used to carry telephone signals. Signal travels at 200,000,000 m/s r
Optical Fibres i Advantages (compared to wires) r Cheaper, lighter, carry more signals little energy loss
Satellites The higher the satellite The longer its period (time for one revolution round the Earth)
Satellites Geostationary satellite Takes 24 hours to make one revolution (stays above same point on Earth’s surface)
Curved Reflectors Large area collects more energy concentrates signal on detector
Curved Reflectors Curved reflector Receiver at the focus
Curved Reflectors Curved reflector transmitter at the focus