Physics P4

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ELECTROSTATICS

  • The chance of getting an electric shock can be reduced by : 1) correct earthing. 2) standing on insulating mats. 3) wearing shoes with insulating soles. 4) bonding fuel tanker to aircraft
  • Electrostatic effects are caused by the transfer of electrons
  • A positively charged object lacks electrons
  • A negatively charged object has extra electrons
  • Like charges repel
  • Unlike charges attract
  • Uses of electrostatics include : defribrillators, paint and crop sprayers, dust precipitators, and photocopiers
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USING ELECTRICITY SAFELY

  • In a three pin plug : 1) live wire is at high voltage. 2) neutral wire completes the circuit. 3) earth wire is connected to the case to prevent it becoming live.
  • Double insulated appliances do not need an earth wire
  • power = voltage x current
  • The fuse (or circuit breaker) is in the live wire. If the current is greater than the rating, the fuse will melt (or circuit breaker break), breaking the circuit
  • resistance = voltage / current
  • Longer wires have more resistance
  • Thinner wires have more resistance
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ULTRASOUND

  • Medical uses include : 1) scans to see inside the body without surgery. 2) measuring the rate of blood flow. 3) breaking up kidney stones
  • Ultrasound is above 20,000 Hz which is a higher frequency than humans can hear
  • Longitudinal waves - e.g. sound and ultrasound
  • Transverse waves - e.g. light
  • Wavelength is the distance occupied by one complete wave
  • Frequency is the number of complete waves in one second
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NUCLEAR RADIATION

  • Gamma rays are given out from the nucleus of certain radioactive materials
  • X-Rays are made by firing high speed electrons at a metal target
  • Nuclear radiation is emitted from the nucleii of radioisotopes : 1) alpha particle is a helium nucleus. 2) beta particle is a fast-moving electron. 3) gamma radiation is a short wavelength electromagnetic wave
  • Fission is the splitting up of a large nucleus
  • Fusion is the joining together of smaller nucleii
  • Both release a lot of energy
  • Fission is currently used to generate electricity
  • Fission leads to a chain reaction which must be carefully controlled
  • Medical uses include : 1) diagnosis, as a tracer. 2) sterilising equipment. 3) treating cancers
  • Other used include : 1) smoke detectors. 2) industrial tracers. 3) dating rocks and archaeological finds
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