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41 Cards in this Set
- Front
- Back
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What is light? |
One of the family of radiations called the electromagnetic spectrum |
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How does a beam of electromagnetic radiation transfer emerge? |
In 'packets' called photons |
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What is the link between the frequency of electromagnetic radiation and the energy tanferred by photons? |
The higher the frequency of electromagnetic radiation, the more energy is transferred by each photon |
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List the electromagnetic radiations in order of frequency |
Radio waves, microwaves, infrared, visible light, ultraviolet, X rays, gamma rays |
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What speed done the types of electromagnetic radiation travel at? |
They all travel at exactly the same speed through space (a vacuum) of 300 000 km/s |
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How do u measure the intensity of a beam of electromagnetic radiation? |
The energy arriving at a square meter of surface each second |
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What does the energy transferred to an absorber by a beam of electromagnetic radiation depend on? |
Both the number of photons arriving and energy of each proton |
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What is the link between the intensity of of a beam of electromagnetic radiation and distance? |
The intensity of a beam of electromagnetic radiation decreases with distance from the source |
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What do some electromagnetic radiations have enough energy to do? |
Ultraviolet radiation, X rays and gamma rays have enough energy to change atoms or molecules, which can initiate chemical reactionx |
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What can cause ionisation? |
High energy ultraviolet radiation, X rays and gamma rays |
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What can electromagnetic radiations that are ionising do? |
Have a high enough photon energy to remove an electron from an atom or molecule |
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What can the heating effect of absorbed radiation do? |
Damage living cells |
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What happens to some microwaves? |
They are strongly absorbed by water molecules and so can be used to heat objects containing water |
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What do the metal cases and door screens of microwave ovens do? |
Reflect and absorb microwave radiation and protect users from the radiation |
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What do radioactive materials do? |
Emit ionising gamma radiation all the time |
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What happens with increased exposure to ionising radiation? |
The damage to living cells increases leading to cancer or cell death |
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What does the ozone layer do? |
Absorb ultraviolet radiation emitted by the sun, producing chemical changes in that part of the atmosphere |
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What does the ozone layer protect? |
It protects living organisms from some of the harmful effects of UV radiation |
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What can absorb some of the UV radiation from the sun? |
Clothing and sun screens |
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What can physical barriers do to ionising radiation? |
Absorb some of it |
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What do all objects do? |
Emit electromagnetic radiation with a principle frequency that increases with temperature |
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What is the earth surrounded by? |
An atmosphere which allows some of the electromagnetic radiation emitted by the sun to pass through |
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What does radiation from the sun do to the earth? |
It warms the earth's surface when it is absorbed |
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What happens to radiation emitted by the earth? |
It has a lower principle frequency than that emitted by the sun It is absorbed or reflected back by some gases in the atmosphere, this keeps the earth warmer than it would otherwise be and is called the greenhouse effect |
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What is one of the main greenhouse gases in the earth's atmosphere? |
Carbon dioxide which is present in very small amounts |
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What are other greenhouse gases? |
Methane and water in very small amounts |
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What is the rise in atmospheric carbon dioxide largely the result of? |
Burning increases amounts of fossil fuels as an a energy source Cutting down or burning forests to clear land |
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What do computer climate models provide evidence of? |
That human activities are causing global warming |
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What 3 things can global warming result in? |
1.) It being impossible to continue growing some food crops in particular regions because of climate change 2.) More extreme weather events due to increased convection and larger amounts of water vapour in the hotter atmosphere 3.) Flooding of low lying land due due to rising sea levels, caused by melting continental ice and expansion of water in oceans |
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The electromagnetic radiation of some frequencies can be used for transmitting information since: |
1.) Some radio waves and microwaves are not strongly absorbed by the atmosphere so can be used to carry information for radio and TV programmes 2.) Light and infrared radiation can be used to carry information along optical fibres because the radiation travels large distances through glass without being significantly absorbed |
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Why is some information superimposed on to an electromagnetic carrier wave? |
To create a signal |
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What is an analogue signal? |
A signal which can vary continuously |
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What is a digital signal? |
A signal that can usually only make 2 discrete values |
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How can sound and images be transmitted? |
Digitally, with a digital signal |
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What is digital code made up of in digital transmission? |
Just two symbols '0' and '1' |
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How can coded information be carried? |
By switching the electromagnetic carrier wave off and on to create short bursts of waves (pulses) where '0' is no pulse and '1' is a pulse |
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What happens when waves are received? |
The pulses are decoded to produce a copy of the original sound wave or image |
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What is the advantage of digital signals over analogue signals? |
If the original signal is affected by noise it can be recovered more easily |
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What is the amount of information needed to store and image or sound is measured in? |
Bytes (B) |
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What is the link between information stored and quality of sound? |
Generally the more information stored the higher the quality of sound or image |
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What is an advantage if using digital signals? |
The informations can be stored and processed by comoutors |
