Uses of EM radiation Flashcards
(35 cards)
How do long wave radio waves travel far distances?
They bend around the curved surface of the Earth, including round hills, tunnels, etc.
How can radio waves be used?
Broadcasting TV and radio signals
Transmitting satellite signals
Wifi wireless connections
Why must you be in direct sight of TV and fm radio transmitters to get a signal?
The signal doesn’t bend around hills or travel far through buildings.
Why can short wave radio signals (like long wave) be received at long distances from the transmitter?
They are reflected from the ionosphere - an electrically charged layer in the earths upper atmosphere.
Why are some very short wave radio waves be used for satellite communications?
They can pass through the ionosphere.
What are the uses of microwaves?
Carry tv and satellite signals.
Mobile phone signals.
Cooking in microwave ovens.
For satellite communication, what type of microwaves do you need?
Microwaves that can pass easily through the earths watery atmosphere.
How does satellite tv work?
The signal from a transmitter is transmitted into space, where it’s picked up by the satellite receiver dish orbiting above the earth. The satellite transmits the signal back to earth in a different direction where it’s recorded by a satellite dish on the ground.
Why is there a slight time delay between the signal being sent and received from satellite tv?
The long distances the signal has to travel.
Why do microwave ovens use different microwave wavelengths from satellites?
In conmunications, the microwaves used need to pass through the earths watery atmosphere.
In microwave ovens, the microwaves need to be absorbed by water molecules in food to be able to heat it up - so they use a different wavelength to those in satellite communications.
How does microwaves heat food up in microwave ovens?
The microwaves penetrate up to a few centimetres into the food before being absorbed by water molecules. The energy from the absorbed microwaves causes the food to heat up. The heat energy is then conducted or convected to other parts of the food.
How is infrared used?
Thermal imaging on CCTV cameras and night vision equipment Optic fibre cables Grills and toasters Remote controls Security systems by infrared sensors
Why is thermal imaging used in daytime too?
It can pass through fog.
How can infrared be used to monitor temperature?
All warm objects off heat as IR radiation. So infrared can be used to monitor temperatures - heat loss through a houses uninsulated roof can be detected using infrared sensors.
Infrared is also detected using night vision equipment. The equipment turns it into an electrical signal which is displayed on a screen as a picture. This can be used to detect people at night.
How do optical fibres use infrared to transmit data?
Optic fibres carry data over long distances as pulses of infrared radiation.
They work by bouncing waves off the sides of a thin inner core of glass or plastic. The wave enters one end of the fibre and is reflected repeatedly until it emerges at the other end.
How is visible light used?
Vision
Photography
How can visible light allow us to see the EUrion pattern?
The EUrion pattern can be seen when illuminated because it reflects certain wavelengths of visible light. These wavelengths can be detected using our eyes or photographic equipment.
Why can we seem objects?
They’re illuminated - they give out or reflect light.
How do our eyes use visible light to see?
When light enters the eye, it gets refracted through the lens and focused onto the retune at the back of the eye. The retina sends messages to the brain via the optic nerve which then interprets it.
How does photography use visible light?
Cameras use a lens to focus visible light onto a light sensitive film or electronic sensor.
How is ultraviolet radiation used?
Detect forged bank notes
Security marking
Disinfect water and sewage
What is fluorescence?
A property of certain chemicals, where ultraviolet radiation is absorbed and then visible light is emitted.
How can UV detect forged banknotes?
Banks print special markings in fluorescent ink on bank notes to detect forgeries. Under a UV light, genuine notes will display the fluorescent markings but fake notes are printed in cheap paper that’s slightly fluorescent so under UV light they’ll glow all over and there won’t be any markings.
What are fluorescent lamps?
Lamps which works by fluorescence. They produce UV radiation, which is absorbed by a coating inside the bulb and re emitted as visible light. They are used in security lights.
