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OCR P2
OCR 21st Century Science P2
| Question | Answer | |||
|---|---|---|---|---|
| In a general model of radiation: one object (a []) emits [] | source--radiation--; the radiation travels [] from the source and can be []ed, []ed, []ed (or a [] of these) by [] it encounters | outwards--reflected, transmitted or absorbed--combination--materials--; radiation may affect an object (a []) some distance away, when it is [] | detector--absorbed. | |
| Light is one of a family of [] called the [] [] | radiations--electromagnetic spectrum--. | |||
| A beam of electromagnetic radiation transfers energy in 'packets' called | photons. | |||
| The higher the frequency of an electromagnetic radiation, the more [] is transferred in each [] | energy--photon--. | |||
| The electromagnetic radiation (in order of frequency): | radio waves, microwaves, infrared, (^red)visible light(^violet), ultraviolet, X-rays, gamma rays. The bracketted items denote that the visible light spectrum goes from [] to [] | red to violet. | ||
| All types of electromagnetic radiation travel at exactly the same [] through a vacuum in space | speed - [] km/s | 300,000, | ||
| Intensity of electromagnetic radiation |on a unit area| = | number of photons per second x energy of each photon, hence the e[] arriving at a square metre of surface each second is a useful measure of intensity | energy--. | ||
| The energy transferred to an absorber by a beam of electromagnetic radiation depends on both the [] of photons and each photon's [] | number--energy--. | |||
| intensity ∝ | 1/distance², the distance being between the [] and the [] | source--detector--, this is as the area that the energy is spread over is proportional to the | distance; the larger the area, the less the [] per unit area, hence the less the [] | energy--intesity--. |
| As intensity ∝ | 1/distance², as distance (from the source to the detector) increases, the intensity | decreases. The reason is fractionally due to the fact that there is partial [] of radiation by the [] it travels through | absorption--medium--, and the absorbed amount increases with the [] that the radiation travels | distance--. |
| Some electromagnetic radiations (ultraviolet radiation, X-rays, gamma rays) have enough [] to change [] or [] | energy--atoms or molecules--, which can intiate | chemical reactions. | ||
| High energy ultraviolet raidation, X-rays and gamma rays can cause | ionisation. | |||
| Which electromagnetic radiations have enough energy to change atoms or molecules? | ultraviolet, X-rays, gamma rays. | |||
| The electromagnetic radiations which are ionising are those with high enough [] energy to [] an [] from an atom or molecule | photon--remove--electron--: this is known as | ionisation. | ||
| The h[] effect of [] radiation can damage [] cells | heating--absorbed--living--. | |||
| All forms of electromagnetic radiation deliver e[] | energy; this will [] the material that absorbs the radiation | heat--. The amount of heating is proportional to the [] of the radiation and the [] of [] the radiation is absorbed for | intensity--length--time--. | |
| Some poeple have concerns about health risk from low [] [] radiation | intensity microwave--, for example from m[] [] []sets and m[], | mobile phone handsets and masts, but the evidence for this is | disputed. | |
| Some m[] are strongly absorbed by water molecules and so can be used to [] objects containing water | microwaves--heat--. | |||
| The metal cases and door screens of microwave ovens [] or [] microwaves radition and so protects users from the radiation | reflect--absorb--. | |||
| Some materials (i.e. radioactive materials) emit [] [] radiation [] of the time | ionising gamma--all--. | |||
| With increased exposure to ionising radiation, [] to [] cells increases, | damage--living--, enventually leading to [] or [] death | cancer--cell--. | ||
| The [] layer absorbs ultraviolet radiation emitted by the [] | ozone--Sun--, producing [] changes in that part of the [] | chemical--atmosphere--. | ||
| As the ozone layer absorbs some ultraviolet radiation emitted by the Sun, it protects living organisms from some of the radiation's [] effects | harmful--. | |||
| Sun-screens and clothing can be used to [] some of the ultraviolet radiation from the Sun | absorb. | |||
| Physical barriers [] some ionising radiation | absorb--, for example: X-rays are absorbed by [] materials | dense--so can be used to show shadow pictures of []s in our body or of objects in aircraft passengers' [] | bones--luggage--, and radiographers are protected from radiation by [] materials such as [] and [] | dense--lead--concrete--. |
| All object emit [] radiation with a [] frequency that increases with [] | electromagnetic--principal--temperature--. | |||
| The Earth is surrounded by an [] which allows some of the [] radiation emitted by the [] to pass through | atmosphere--electromagnetic--Sun--. | |||
| The radiation emitted by the Earth, which has a []er p[] f[] than that emitted by the Sun | lower principal frequency--, is [] or [] back by some [] in the atmosphere | absorbed--reflected--gases--; this keeps the Earth []er than it would otherwise be and this is called the [] [] | warmer--greenhouse effect--. | |
| One of the main g[] gases in the Earth's [] is carbon dioxide | gases--atmosphere--, which is present in very [] amounts | small--. | ||
| Apart from carbon dioxide, other greenhouse gases include m[] which is present in very [] amounts, and [] v[] | methane--small--water vapour--. | |||
| The amount of carbon dioxide in the atmosphere is controlled by the | carbon cycle. Processes that remove carbon dioxide from the air: [] by plants, [] in the oceans | photosynthesis--dissolving--. Processes that return carbon dioxide to the air: [] by plants, animals and microbes; c[] (i.e. [] wood and fossil fuels such as coal, oil and gas) | respiration--combustion--burning--; carbon dioxide is also given out by t[] d[] of limestone, like in the manufacture of iron, steel and cement | thermal decomposition--. |
| For thousands of years, the processes in the carbon cycle were c[] | constant, so the percentage of carbon dioxide in the atmosphere did not | change. | ||
| Over the past 200 years, the percentage of carbon dioxide in the atmosphere has [] steadily because humans are: [] more and more fossil fuels as [] sources | increased--burning--energy--; and [] large areas of forest to [] land, meaning that there is less [] removing carbon dioxide from teh air | burning--clear--photosynthesis--. | ||
| Computer generated [] models, based on diffent amounts of [] [] in the atmosphere, have produced the same changes as have been [] in the real world | climate--carbon dioxide--observed--. The computer climate models provide [] that [] activities are causing global warming | evidence--human--. | ||
| Due to global warming, it may become impossible to continue growing some food crops in particular regions because of | climate change. | |||
| Global warming may result in more e[] weather events | extreme--, due to increased c[] and larger amounts of [] [] in the []er atmosphere | convection--water vapour--hotter--. | ||
| One consequence of global warming could be the [] of low lying lands due to rising [] levels | flooding--sea--, caused by []ing c[] [] and expansion of [] in the oceans | melting continental ice--water--. | ||
| The electromagnetic radiation of some frequencies can be used for transmitting i[] | information, since: (a)some [] waves and []s are not strongly [] by the atmosphere | radio--microwaves--absorbed--, so can be used to carry [] for radio and TV programmes | information-- (b)l[] and [] radiation can be used to carry information along [] fibres because the radiation travels large distances through [] without being significantly [] | light--infrared--optical--glass--absorbed--. |
| Information can be superimposed onto an [] c[] wave, to create a [] | electromagnetic carrier wave--signal--. | |||
| A signal that can vary continuosly is called an | analogue signal. | |||
| A signal that can only take a small number of discrete values (usually two) is called a | digital signal. | |||
| Sound and images can be transmitted d[] (as a [] signal) | digitally--digital--. | |||
| In digital transmission, the digital code is made up from just two symbols - '[]' and '[]' | 0--1--. The coded information can be carried by switching the [] [] wave [] and [] to produce short burst of [] (p[]) where '0' = no [] and '1' = [] | electromagnetic carrier--on--off--waves--pulses--pulse--pulse--. | ||
| When the aforementioned waves are received, the p[] are [] to produce a [] of the original sound wave or image | pulses--decoded--copy--. | |||
| An important advantage of [] signals over [] signals is that if the original signal has been affected by noise it can be recovered more easily | digital--analogue--. This is because the noise is usually lower in [] than the [] states of the digital signal | amplitude--'on'--, hence the electronics in the amplifiers can [] the noise and it doesn't get [] along | ignore--passed--. As a result digital signals maintain their q[] better than analogue signals | quality--. |
| The amount of information needed to store an image or sound is measured in [] ([]) | bytes (B). | |||
| Generally, the more information stored, the higher the [] of the sound or image | quality--. | |||
| An advantage of using digital signals is that it can s[] and p[] by computers | stored--processed--. |
Created by:
Toluo
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