distance speed x time dvt Speed of sound

distance = speed x time d=vt

Speed of sound

340 m/s

Speed of light

300, 000 m/s

transmitter

transmitter sends signals

receiver

receiver replays signals

microphone energy change

microphone Sound electrical

loudspeaker energy change

loudspeaker electrical sound

frequency Number of waves per second

Wavelength l Amplitude

High frequency

Low frequency

High amplitude

Low amplitude

wave speed v

speed = frequency x wavelength v=fl

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 radio a. m.

Diffraction Bending round obstacles

Diffraction Long wavelength, low frequency bends more than short wavelength, high frequency

Television aerial tuner decoder (vision) decoder (sound) amplifier TV tube Loudspeaker

Television Line build-up Lines made by electron beam moving backwards and forwards across screen The lines build up to make picture

Television Brightness variation Light areas – many electrons Dark areas – few electrons

Television Image retention 25 pictures per second Eye retains image for short time – 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 magenta yellow white green blue cyan

Reflection Angle of = incidence reflection i=r i mirror r

Refraction air glass

Total Internal Reflection Above a certain angle (the critical angle), the light is reflected. i r

Optical Fibres Used to carry telephone signals. Signal travels at 200, 000 m/s i r

Optical Fibres Advantages (compared to wires) Cheaper, lighter, carry more signals little energy loss i r

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