GCSE Physics

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Author:
ghoran
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184217
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GCSE Physics
Updated:
2012-11-18 12:18:23
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  1. how does a smoke detector work 
    a smoke detector uses the radiation from americium-241 oxide . the substance emitts alpha radiation . the alpha radiation ionises molecules in the air inside smoke detectors and this allows electric current to flow . however particles of smoke will absorb the radiation . this stops the electric current and causes the alarm to switch on 
  2. why does a smoke detector use alpha radiation rather than  beta or gamma radiation 
    betas and gammas are not effected by the smoke and they dont have a strong enough ionisng power to be detected , beta and gamma could also be dangerous to humans ,
  3. explain how the somke detector works in brief 
    as long as the electric current flows the alarm is quiet , the smoke stops the alphas so no ionisng and no current 
  4. what is tracing 
    very tiny amounts of radioactive substances can be detected by the radiation they emit . so a tiny amount of a radioistope mixed with the substance canb act like a tag or label , to show what's happening to the substance 
  5. how canb tracing help trace leaks
    tiny amounts of radioistopes can be added to fluid in pipes to trace leaks underground . the area around the leak will be come radioactive , which can be discovered using a geiger muller tube and counter 
  6. how can tracing be used in medicine 
    for example ,  doctor might suspect that a patient has a blocked kidney . a small amount of I which is radioactive , is injected into the patient . Both kidneys should extract the iodine from the bloodstream in 5 minutes and then pass it into the urine . A geiger counter is held over each kidney and the readings show whether the iodine stays in the kidney or whether it passes out 
  7. what would an unblocked kideny with iodine look like on a graph
    • with count rate on the y axis instead 
  8. what would a blocked kidney with idoine look line on a graph 
  9. how are gamma rays used in medicine 
    high doses of radiation can kill cells : they are used to kill cancer cells , which are more easily killed than healthy cells . Gamma radiation having the highest penetrating power is used to kill cancer cells . the radioistope of cobalt 60Co , is generally used as the source of gamma radition 
  10. how is radiation used in steralisation 
    • steralisation is achieved by killing microorganisms with gamma radiation (gamma radiation is used because of its penetrating power) . examples of this use of gamma radiation include the steralisation of 
    • 1) foods . bacteria , moulds and insects can be killed in foods , even after they are pacakged . this makes the shell life longer , but may also alter the taste
    • 2) hospital equioment , especially plastic syringes that would be destroyed by heat 
  11. what is half life 
    the time it takes for the count rate from a sample containing the isotope to fall to half its initial level 
  12. during radioactive deacy , nuclei disintergrate at 
    random at a rate which is unaffected by chemical chnage or temperature 
  13. if one half life has elapsed what fraction of the parent isotope is remaining and what fraction of parent radioistope is decayed 
    • radioistope remaining = 1/2
    • radioistope decayed = 1/2
  14. if 2 half life has elapsed what fraction of the parent isotope is remaining and what fraction of parent radioistope is decayed 
    • radioistope remaining = 1/4
    • radioisotope deacyed = 3/4
  15. if 3 half life has elapsed what fraction of the parent isotope is remaining and what fraction of parent radioistope is decayed 
    • remaining = 1/8
    • decayed = 7/8
  16. if 4 half life has elapsed what fraction of the parent isotope is remaining and what fraction of parent radioistope is decayed 
    • remaining = 1/16
    • decayed = 15/16
  17. what is curve for cout rate and time (for radioactive decay)
  18. the nost appropriate radioistope for a particular use depends on
    • the type of radiation emitted 
    • the half life
    • the important factors to conisder are :-
    • how far the radioactivity has to travel to the detector 
    • the material the radiation has to tavel through
    • the hald life 
  19. the longer the half life the
    longer the radioactivity will remain 
  20. complete the table 

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