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Radiation and the universe (summary of AQA module)

Radiation and the universe (summary of AQA module)

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Radiation and the universe (summary of AQA module)

  1. 1. Radiation and the universe summary<br />12 February, 2011<br />
  2. 2. The electromagnet spectrum<br />Electromagnetic waves are electrical and magnetic disturbances that transfer energy from one place to another. <br />Their wavelengths can vary from very long(radio waves) to very short (gamma waves). <br />They travel at 300 000 000 metres per second. <br />The order of the spectrum is: radio, microwaves, infra red, visible, ultra violet, X rays and gamma waves<br />1<br />
  3. 3. Gamma rays and x rays<br />Gamma rays and x rays are very short, high energy and highly penetrating waves.<br />They can be absorbed by denser atoms such as calcium in bones and metals.<br />X rays are used to take radiographs of the body in hospitals.<br />Gamma rays are used to sterilize surgical equipment, kill bacteria in food and kill cancer cells.<br />2<br />
  4. 4. Light and ultra violet waves<br />White light consists of all the colours of the visible spectrum. The colours can be separated by dispersion in a prism.<br />Ultra violet waves are shorter than visible waves and like light can be absorbed, reflected or transmitted through substances.<br />Ultraviolet rays damage the human skin and eyes.<br />3<br />
  5. 5. Infra red, microwaves and radio waves.<br />Infra red waves are emitted from hot objects and are used in scanners, optical fibres and remote hand sets.<br />Microwaves are used in heating food (ovens) and communications (mobile phones).<br />Radio waves are used in communications – the longer waves diffract better so can be transmitted over longer distances.<br />4<br />
  6. 6. Communications<br />5<br />Radio waves are extensively used for communications. Different frequencies have different uses including: radio, FM radio, TV, mobile phones and satellite links.<br />Higher frequency waves carry more information but have a short range because they are absorbed by the atmosphere and don’t diffract (bend around corners)much.<br />The ionosphere reflect the longer waves.<br />Optical fibres carry information in the glass fibre as it reflects along the thin fibre.<br />
  7. 7. Analogue signals<br />Analogue signals are wave signals that vary continuously in amplitude and frequency. Example is a microphone. <br />The signal is transmitted in a carrier wave from a transmitter to a receiver.<br />Analogue waves are subject to interference so they often carry a lot of noise and distortion.<br />6<br />
  8. 8. Digital signals<br />A digital signal is a series of pulses. The voltage of the pulse is either high (1) or low (0). Each pulse is called a bit.<br />Digital signals are also set by carrier waves to a receiver. However the receiver can clean the noise from the pulses so there is no interference. <br />Digital signal carry more pulses per second than analogue.<br />These are used in mobile phones, radio and computers.<br />7<br />
  9. 9. Nuclear radiation<br />Many of the larger, heavier atoms are unstable and release radiation to become more stable.<br />The radiation can be detected by a Geiger counter and photographic film.<br />Radioactive decay is a random event for a particular atom but occurs regularly when large numbers of atoms are present.<br />The radiation released is dangerous as the high energy particles or waves can destroy or modify cells causing cancer.<br />8<br />
  10. 10. Alpha particles<br />Alpha particles are helium nuclei – they have a mass of 4 atomic mass units and a charge of +2.<br />These particles are released from the nucleus of an unstable atom.<br />They have a short range in air (about 10 cm) and are absorbed by paper.<br />They are very dangerous inside living cells.<br />8<br />
  11. 11. Beta particles<br />Beta particles are electrons which have been emitted from the nucleus of an unstable atom. <br />They have a very small mass and a charge of -1.<br />These particles can penetrate paper but are absorbed by thin metal sheets. (1cm aluminium).<br />They are dangerous from outside the living cell.<br />10<br />
  12. 12. Gamma radiation<br />Gamma rays are very short wave, high frequency electromagnetic radiation.<br />They have no mass and no charge.<br />They are highly penetrating and can only be stopped by thick lead sheet or very thick concrete.<br />There range in air is unlimited.<br />They easily penetrate living cells from outside the body.<br />11<br />
  13. 13. Half life of a radioactive substance<br />Radioactive atoms decay at random, however when there are large number of the atom present the average rate of decay can be predicted.<br />The half life of a radioactive substance is the time it takes for half of the active unstable particles to decay.<br />The number of radioactive particles decreases in the sequence 1: ½:1/4: 1/8 and so on for every subsequent half life. <br />The level of radiation is measured ona a Gieger counter.<br />12<br />
  14. 14. Radioactivity at work<br />Some uses of radioactive particles are:<br />(1) Thickness monitoring – using a beta particle source attached to detector which applies varied pressure to rollers.<br />(2) Radioactive tracers – short half life gamma sources are injected into a patient to track the flow of fluids in the body.<br />(3) Radioactive dating – the amount of radioactive carbon or uranium in material can be used to track the age of past living tissue and rocks respectively. <br />13<br />
  15. 15. The expanding universe<br />The Doppler effect shows that objects in front of a moving source would see light waves shortened (blue shifted) while those behind the source see the waves lengthened ( red shifted).<br />Light from distant galaxies is always red shifted which suggests that they are all moving away from our galaxy.<br />This indicates that the universe is expanding and has been doing this for about 13 billion years.<br />14<br />
  16. 16. The Big Bang<br />The fact that the universe is expanding suggests that all matter was created at one point at one time (singularity) – this was the Big Bang.<br />Since that time all matter in all the galaxies has been moving apart.<br />At the start of the universe a huge amount of energy was released – this energy is still observable today in the form of background microwave radiation.<br />It is still uncertain as to whether the universe will continue to expand or will eventually collapse under gravity.<br />15<br />
  17. 17. Looking into space<br />The Earth’s atmosphere absorbs all electromagnetic waves expect light, radio waves and some ultra violet rays.<br />For the above reason observing space from the Earth only give a partial view of the universe.<br />Images fro satellites like the Hubble telescope give a true detailed image of the electromagnetic radiation from all the universe.<br />Telescopes and radio telescopes work from the Earth’s surface provided there is no interference for these waves.<br />16<br />

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