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44 Cards in this Set
- Front
- Back
What are the properties of laser light? |
Narrow, intense beams and monochromatic |
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Why are lasers monochromatic? |
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? |
All the waves are in phase |
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What is meant by lasers being coherent? |
The waves have a fixed phase difference |
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Do lasers have low or high divergence? What does this mean? |
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? |
A laser is shone onto the CD and is reflected from the shiny bottom surface as it spins |
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Give 5 examples of uses infrared has |
Cooking: Grills and toasters |
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Why are radiowaves and microwaves good at transferring information over long distances? |
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? |
1km-10km |
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Why can long-wave radio waves be transmitted from one place and recieved halfway round the world? |
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) |
10cm-10m |
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Why must you be in direct sight of the transmitter to recieve TV and FM radio transmissions? |
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? |
10m-100m |
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Why can short-wave radio signals be recieved at long distances? |
Because of their reflection in the ionosphere |
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What is diffraction? |
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? |
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? |
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? |
It changes speed |
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What is refraction? |
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? |
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? |
Short wave (10m-100m) and medium wave (300m) |
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What does the amount a wave is refracted in the ionosphere depend on? |
Its frequency and the angle of elevation |
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Why is refraction sometimes a negative thing? |
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? |
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) |
Multiplexing = this is when many different signals are compressed and transmitted as a single wave. |
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Give one advantage and two disadvantages of DAB radio |
Adv = Less interference |
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What waves electromagnetic wave is used for communication to and from satellites? |
Microwaves |
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What must the wavelengths two properties be to be used for communication to and from satellites? |
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 |
A signal from the transmitter is transmitted into space |
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Why could a mobile mast be dangeous? |
The absorption of microwaves in water molecules causes cells to be burnt or killed |
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What is the difference between analogue and digital signals? |
Analogue is a variable signal and can take on any value of a certain range |
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What are the two advantages of digital signals to analogue signals? |
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 |
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Why does spending time in the sun increase the risk of skin cancer? |
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? |
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? |
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? |
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? |
Shocks waves travel through the earth |
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How are seismic waves recorded? |
Seismographs |
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What do P-waves travel through? |
Solids and liquids |
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What do S-waves travel through? |
Only solids |
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Which seismic waves are faster? |
P-waves |
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Are P-waves longitudinal or transverse? |
Longitudinal because the vibrations occur <-> |
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Are S-waves longitudinal or transverse? |
Transverse because the vibrations occur up and down |
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How do seismic waves tell us about the Earth's structure? |
P-waves refract = density change = mantle and core |