Uses of EM waves

Uses of Radio waves

Radio and TV stations

Bluetooth

Long-wave radio waves

can diffract around Earth’s curved surface and hills and tunnels

so radio signals are received when receiver isn’t in line of sight of transmitter

Short-wave radio waves

reflected from ionosphere (electrically charged layer)

How does Bluetooth use short-wave radio waves?

send data between devices

Radio waves for FM radio and TV…

short-waves so must be in line of sight of receiver

Uses of microwaves

Satellite TV and phones- easily passes through watery atmosphere

Microwaves

How do satellites use microwaves?

1. Transmitter transmits signal into space

2. Satellite dish orbiting earth receives signal and transmits it in a different direction

3. It is then received by a satellite dish on earth but there is a time delay due to long distance

How do microwaves heat food?

1. Microwaves penetrate into food and transfer energy to water molecules

2. the rest of the food is heated by conduction or convection as the internal energy increases the rest of the particles heat up

Uses of IR

IR cameras

Toasters

Electric heaters

How do IR cameras work?

1. Detect IR and turns it into electrical signal

2. More IR means stronger electrical signal so object appears brighter

How is IR used in toasters?

1. IR doesn’t penetrate deep into bread

2. so inside is heated by conduction

How do electric heaters work?

1. Long wire inside heater emits IR when current flows through it

2. IR transfers energy to thermal energy stores of objects

How is visible light used in fibre optic cables?

Light is reflected back and forth by solid glass or plastic walls until end of fibre

How do fluorescent lights use UV?

UV is absorbed and re-emitted as visible light by phosphor

How do security pens use UV?

ink will glow under UV light

How is UV used for suntans?

UV lamps produce UV which gives artificial suntans

How are X-rays geneated?

1. X-rays can pass through less dense materials like flesh so these appear black

2. they cannot pass through bones so these appear white

How are x-ray and gamma waves used to destroy cancerous cells?

small doses are directed at cancerous cells from all direction

too much may destroy other living cells

How are gamma rays used in medical tracers?

gamma source is injected into patient and path is traced