Flashcards
Electromagnetic Waves
Flashcards do conjunto (13)
- 1Electromagnetic WavesPhysics 1b 3.1 - 3.3
- 2What is the electromagnetic spectrum?
- 3What speed do EM waves travel at in a vacuum?3 x 10^8 m/s
- 4What is the correlation between frequency and wavelengths of EM waves?Waves with a higher frequency have shorter wavelengths.
- 5What are radio waves used for?Long-wave radio waves (1 - 10km) can be transmitted from London and received half way around the world because long wavelengths diffract around the curved surface of the Earth. This means that radio signals can be received even if the receiver isn't in line of sight of the transmitter.
- 6How do radio waves used for TV and FM radio work?They have very short wavelengths (10cm - 10m), to get reception you must be in the direct line of sight of the transmitter - the signal does not easily diffract. Short-wave radio signals (10m-100m) can be received at long distances from the transmitter. This is because, they are reflected from the ionosphere - an electrically charged layer in the Earth's atmosphere. Medium-wave radio signals are also reflected from the ionosphere depending on atmospheric conditions. and the time of day.
- 7What use do microwaves have?Communications to and from satellites uses microwaves, such as mobiles and television. They can pass easily through the Earth's watery atmosphere unlike radio waves.
- 8How does satellite television work?The signal from a transmitter is transmitted into space, where it is picked up by a satellite's receiver dish orbiting thousands of kilometres above the Earth. The satellite transmits the signal back to Earth in a different direction where it is received by a satellite dish on Earth.
- 9How do mobile phone calls work?They travel as microwaves from your mobile to the nearest transmitter, some microwaves are absorbed by water molecules and heat them up. If the water in question happens to be in your cells, this can have a damaging effect. The microwaves are used by remote-sensing satellites - to see through the clouds and monitor oils spills, track the movement of icebergs and see how much rainforest has been cut down.
- 10Give two waves that infrared waves are used.1) in remote controls
2) optical fibres - 11How do remote controls work?By emitting different patterns of infrared waves to send different commands to an appliance (eg. your television).
- 12How do optical fibres use infrared waves?They can carry data over long distances, they use both infrared and visible light to transmit this information. The signal is carried in pulses of light and infrared radiation, it is then reflected off the sides of a very narrow core from one end of the fibre to the other.
- 13How do cameras work?They use a lens to focus the visible light reflected from an object onto light-sensitive film or an electronic sensor (CCDs). The lens aperture controls how much light enters the camera, the shutter speed determines how long the film or sensor is exposed to the light. By varying the aperture and shutter speed, a photographer can capture as much or as little light as they want in their photograph.
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- FlashCards sobre Electromagnetic Waves, criado por Lauren Adams em 13-05-2016.
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- Lauren Adams
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