P4

P4

1. equations

   • resistance=voltage/current
   • power=voltage X current

2. static electricity

   • problems
     • industrail
       • flour factories, flour passes through a pipe and becomes charged. a spark can cause an explosion
         • metal strap attached to a metal vat which is earthed
       • petrol tankers, charge can build up due to friction on tyres or petrol through a pipe, a spark can cause an explosion
         • metal strap earths the tanker.
       • re-fuelling aeroplanes, friction between the pipe and fuel causes charge to build up, spark can cause explosion
         • pipe nozzle is connected to a earth strap
     • everyday
       • dirt and dust attracted to t.v
       • clothes cling to skin
     • antistatic devices
       • sprays, liquids and dusters can be made of conducting material
       • dryer sheets use oil to prevent charge build up on tumble dryers
   • Uses
     • spray painting, paint particles become charged due to friction and repel eachother. object is opposite charge so they stick together
       • reduces waste paint
       • object has even coat
       • paint covers awkward spots
     • electrostatic dust precipitators, metal grid is negative which causes dust to become negative, dust is then attracted to positive plates
     • defibrillator
       • two charged paddles are put in contact with a patient's chest and a charge is passed through causing the heart to contract
       • care is taken not to shock the operator

3. wire, current and resistance

4. waves

   • ultra sound
     • longditudinal wave with a high frequency that humans can't hear
     • used to check up on the development of babies
     • breaks up kidney stones by vibrating them.
     • used to measure the speed of blood through a blood vessel
     • better than X-rays as it doesn't harm tissue
   • nuclear radiation
     • alpha beta gamma
     • radioactivity of an object is measured by nuclear decays or counts per minute. radioactivity decreases with time
     • ionising radiation causes cancer
     • radioactivity is caused by unstable atoms
     • smoke alarms
       • uses alpha radiation
       • alpha radiation hits air particles, these become charged and complete a circuit. smoke stops this happening as alpha radiation is absorbed by the smoke, the alarm sounds
     • tracers
       • uses gamma radiation
       • a radioisotope that emits gamma radiation is put into a pipe, a detector is the passed along the surface of the ground and tracks the radiation. and increase in activity suggest leak.
       • also used to find a route of a pipe, track disposal of waste,check uptake of fertiliser in plants
   • half life
     • can be used to age objects like bones
     • is the time taken for half of a radioactive substance to decay
       • short half life
       • long half life

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