Physics: Radiation For Life

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  • Physics: radiation for life
    • static electricity
      • static is caused by friction
      • electrons negative
      • lack of electrons means positive charge
      • opposites attract
    • more on static electricity
      • disadvantages: attracts dust, clothes cling, shocks from metal
      • dangerous if sparks near gases
      • earthing allows charge to take easy route
      • insulators stop charge reaching you
    • uses of static electricity
      • paint sprayers opposite charge to car
      • dust precipitators, dust attracted to metal plaes
      • defibrillators,electricity makes heart contract
    • charge in circuits
      • current - flow of electrical charge, amps
      • voltages - driving force, volts
      • resistamnce- slows current, ohms
      • broken circuit = no current
    • plugs and fuses
      • live wire - brown - voltage
      • neutral wire - blue - completes circuit
      • earth wire - brown and yellow - safety
      • anything with non conductive case is double insulated
      • fuses melt at high currents
      • circuit breaks can be reset
      • power = voltage x current
    • resistance
      • variable resistors can be changed
      • resistance increase, current decrease
      • longer wires have more resistance
      • thinner wires have more resistance
      • resistance = voltage / current
    • ultrasound treatment and scans
      • sound is longitudinal
      • made of compression and rare factions
      • compressions are high pressure, rarefactions are low pressure
      • wavelength - crest to crest
      • frequency - complete wavers per second, hertz
      • amplitude - middle line to crest, how loud
      • ultrasound above 2000Hz: kidney stones, body scanning
      • x rays cant see soft tissue and can cause damage
    • radioactive decay
      • alpha beta gamma
      • alpha particle is helium nucleus
      • mass and atomic numbers should balance on both sides of nuclear equations
    • radioactivity and half life
      • as more unstable nuclei decay, radioactivity decrease
      • activity never reaches zero
      • time taken for half the radioactive nuclei now present to decay
      • work out half life in steps
    • ionising radiation
      • nuclear radiation and x rays are ionising radiation
      • ionisation occurs because particles lose or gain electrons
      • beta makes atoms negative
      • alpha makes atoms positive
      • low doses of this mutates and multiplies cells causing cancer
      • alpha more dangerous inside body
      • gamma and beta more dangerous outside body
      • x rays and gamma rays are electromagnetic waves
    • medical uses of radiation
      • gamma rays focused at tumour
      • tracers in medicine with short half lives
      • alpha radiation cannot pass through skin and would not be detected
      • gamma rays sterilise instruments
    • uses of radiation and background radiation
      • to find leaks in pipes similar to medical tracers
      • a weak alpha source is blocked by smoke particles in a smoke detector
      • background radiation comes from: unstable isotopes, cosmic rays, human activity
    • radioactive dating
      • if a half life is known, radioactive isotopes left can be read
      • carbon 14 is used for dating
    • nuclear power
      • nuclear fission splits atoms releasing heat
      • extra neutrons make uranium 235 unstable
      • uranium 236 can then divide rapidly
      • control rods limit the rate of fission by absorbing neutrons
    • nuclear fusion
      • joining of atomic nuclei
      • doesnt leave much waster
      • hard to control or build reactors
      • cold fusion would allow us to generate electricity cheaply

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