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44 Cards in this Set
- Front
- Back
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What are the properties of laser light? |
Narrow, intense beams and monochromatic
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Why are lasers monochromatic?
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All the waves in a laser beam are at the same frequency
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Why do lasers produce an intense beam of light?
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All the waves are in phase
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What is meant by lasers being coherent?
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The waves have a fixed phase difference
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Do lasers have low or high divergence? What does this mean?
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They have low divergence which means the beam is narrow and stays narrow even at long distances
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How are lasers used in CD players?
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A laser is shone onto the CD and is reflected from the shiny bottom surface as it spins
The beam is reflected from lands and pits differently and this difference is picked up by a light sensor They are then turned into electrical signals |
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Give 5 examples of uses infrared has
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Cooking: Grills and toasters
Security systems Remote Controls Optical fibres (instead of visible light) Transmisson of data over short distance |
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Why are radiowaves and microwaves good at transferring information over long distances?
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They don't get absorbed by the Earth's atmosphere as much as waves in the middle of the EM spectrum or at high-frequency end.
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What is the wavelengths of long-wave radio?
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1km-10km
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Why can long-wave radio waves be transmitted from one place and recieved halfway round the world?
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They diffract around the curved surface of the Earth
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What is the wavelength of TV and FM radio transmissions? (Very short)
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10cm-10m
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Why must you be in direct sight of the transmitter to recieve TV and FM radio transmissions?
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The signal doesn't bend around hills or travel far through buildings because there is little diffraction
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What is the wavelength of short-wave radio signals?
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10m-100m
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Why can short-wave radio signals be recieved at long distances?
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Because of their reflection in the ionosphere
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What is diffraction?
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When waves spread out at the edges when they pass through a gap or past an object
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What does the amount of diffraction depend on?
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The wavelength of the wave relative to the size of the gap or obstacle
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Why can longer wavelengths encourter a lot of diffraction?
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They are large compared with the gap or obstacles so they can bend round corners and obstacles
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What happens when a wave meets a boundary of a different density?
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It changes speed
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What is refraction?
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When waves change speed when they pass across the boundary between two substances with different densities causing them to change direction
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What causes refraction in the atmosphere?
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When radio waves travel faster through ionised parts of the atmosphere than non-ionised parts
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What waves are refracted most in the ionosphere? What does this mean for the waves?
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Short wave (10m-100m) and medium wave (300m)
This means they can be recieved a long way from the transmitter |
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What does the amount a wave is refracted in the ionosphere depend on?
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Its frequency and the angle of elevation
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Why is refraction sometimes a negative thing?
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It can bend the wave away from the reciever dish, disrupting the signal
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Why do analogue signals often suffer from interference?
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Because there is a limited number of radio wave frequenices that can transmit a good analogue signal so radio stations use waves of similar frequencies
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How does DAB work? (Digital Audio Broadcasting)
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Multiplexing = this is when many different signals are compressed and transmitted as a single wave.
The DAB radio set then picks up the signal and decodes it |
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Give one advantage and two disadvantages of DAB radio
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Adv = Less interference
Dis = Not many DAB transmitters in the UK and the sound quality is often not as good because of the compression |
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What waves electromagnetic wave is used for communication to and from satellites?
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Microwaves
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What must the wavelengths two properties be to be used for communication to and from satellites?
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Pass easily through the Earth's watery atmosphere without too much absorption
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Describe a satellite TV signal path from the transmitter to the reciever
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A signal from the transmitter is transmitted into space
It is picked up by a satellite reciever dish orbiting Earth The satellite transmits the signal back to Earth in a different direction where its recieved by a satellite dish on the ground |
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Why could a mobile mast be dangeous?
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The absorption of microwaves in water molecules causes cells to be burnt or killed
May damage health |
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What is the difference between analogue and digital signals?
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Analogue is a variable signal and can take on any value of a certain range
Digital can only take on two values = on/off, 1/0 |
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What are the two advantages of digital signals to analogue signals?
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Both signals must be amplified however when amplifying analogue the noise is amplified too but with digital its easier to remove or ignore = high quality signal
Digital can transmit several signals at same time = multiplexing |
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Why does spending time in the sun increase the risk of skin cancer?
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The sun's rays include UV radiation which damages DNA in your cells
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Why does darker skin give some protection against UV rays?
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It absorbs more UV radiation preventing the damaging radiation reaching the more vulnerable tissue deeper in the body
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How does the ozone layer protect us from UV?
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The ozone layer absorbs some of the UV rays from the sun, reducing the amount of UV reaching the Earth's surface
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What effect do CFC's have on the ozone?
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Cause depletion of the ozone layer because they react with ozone molecules and break them up
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What is produced when a earthquake occurs?
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Shocks waves travel through the earth
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How are seismic waves recorded?
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Seismographs
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What do P-waves travel through?
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Solids and liquids
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What do S-waves travel through?
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Only solids
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Which seismic waves are faster?
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P-waves
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Are P-waves longitudinal or transverse?
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Longitudinal because the vibrations occur <->
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Are S-waves longitudinal or transverse?
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Transverse because the vibrations occur up and down
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How do seismic waves tell us about the Earth's structure?
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P-waves refract = density change = mantle and core
S-waves not detected in outer core = liquid P-waves travel faster through middle fo the core = solid inner core S-waves travel through mantle = solid |
