P6 21st Century Science- Uses of EM waves

Brief information of the uses of EM waves. Here's a reminder of the order of the waves and a way to remember them:

Randy- Radiowaves

Men- Microwaves

In- Infrared

Velvet- Visible light

Underwear- Ultra-violet light

eXcite- X-rays

Girls- Gamma rays

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These (along with microwaves) are good at transmitting information over long distances, as they don't get absorbed by the Earth's atmosphere as much as other waves in the EM spectrum.

Radiowaves are used for TV and FM radio transmissions, and for this use, they have very short wavelengths compared to most radio waves (although in comparison, Microwaves used for mobile phone communications have very long wavelengths compared to most microwaves, but are still tiny compared to radiowaves).

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Microwaves and satellite communications

Microwaves are used for communications to and from satellites, including satellite TV and phones. This again is because they easily pass through the atmosphere.

For satellite TV, the signal is transmitted from a transmitter into space, where it is then absorbed by the satellite receiver dish that is orbiting thousands of kilometers above the ground. The b then transmits the signal back to Earth in a different direction, where it is received by a satellite dish on the ground.

The dishes are made of metal. This is because metal reflects microwaves well, and so the dish is able to focus waves onto the receiver, as opposed to absorbing them.

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Microwave ovens

Microwaves in microwave ovens have a different wavelength than those used for satellite communications. These microwaves are absorbed by the water molecules in the food. Before being absorbed by the water molecules, they penetrate a few centimeters into the food. This increases the molecule's kinetic energy. The extra energy is then conducted or convected to other parts of the food.

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These are used by Radiographers in hospitals to take images of people's bones, to see if they have been broken or fractured.

X-rays are easily able to pass through the flesh, however they can't through denser materials such as bone or metal as easily. The image is produced due to the varying amounts of X-ray that is absorbed or not absorbed.

On the image, the brighter bits are where fewer X-rays got through, which is a negative image. In the beginning the plate is all white.

X-ray imaging is also used in airports to check the contents of passenger luggage.

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Infrared and visible light

Both infrared and visible light are used in Optical fibres. They are both great for transmitting information along opitical fibres because the signal doesn't weaken that much as it travels along.

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