distance = speed x time

d = v t

Speed

of

sound

340 m/s

Speed

of

light

300,000,000 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

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 radio a.m.

DiffractionBending round obstacles

DiffractionLong wavelength, low frequency bends morethan short wavelength,

high frequency

Televisionaerial

decoder(vision)

tuner

amplifier

TV tube

decoder(sound)

amplifier

Loudspeaker

TelevisionLine build-up

moving backwards and forwards

Lines made by electron beam

across screen

The lines build up to make picture

TelevisionBrightness variation

Dark areas – few electrons

Light areas – many electrons

TelevisionImage retention

Eye retains image for short time

25 pictures per second

– pictures seen as moving smoothly

Colour televisionThree electron guns

One to hit red dots

One to hit blue dots

One to hit green dots

Colour televisionColour mixing

Red + Blue = MagentaBlue + Green = Cyan

Green + Red = YellowBlue+Green+Red = White

Colour televisionColour mixing

red blue

greenyellow cyanwhite

magenta

ReflectionAngle of incidence

iri = r

mirror

Angle of reflection=

Refraction

air glass

Total Internal Reflection

i r

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