Mains Electricity

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Mains Electricity

  • Hazards-  long cables are trip hazards, forks in toasters, using adapters to power high crrent appliances (house fires), fingers in sockets, 3-pin plugs in bathrooms (water + electricity cause electric shocks- bathroom 3-pin plugs illegal in the UK)
  • Circuit Breakers- work on electromagnetism
    • electromagnet strengthens when live wire's current increases
    • plunger attracted, reset switch activated
    • gap in current exposed - NO CURRENT CAN FLOW
  • Fuses-  long piece of wire which melt at a certain current - UK fuses are 3A, 5A, 13A
    • 230V in UK, 120V US
    • Calculating fuses:- Current= Power/ Voltage
    • - choose fuse slightly higher than operating current
    • APPLIANCES USED FOR HEATING HAVE HIGHER FUSES
  • Residual Current Device-  compares urrent in live and neutral. If current in live is bigger (current flowing through a human) RCDs pivot switch to "off"
  • Mains electricity - alternating current (current changing direction in wire)
  • Batteries- direct current (current flows in one direction round circuit)
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Radioactivity

  • Alpha:-
    • 2 protons, 2 neutrons (helium nucleus) - heaviest , +ve charge
    • stopped by paper, air, skin
    • most ionising, least penetrating
    • alpha decay- atomic no. decreases by 2, mass no. decreases by 4

smoke detectors- americium-241 particles collide w/ air particles knocking electrons free- these electrons then used to create current

  • Beta:-
    • high energy ekectron
    • - -ve charge
    • stopped by aluminium
    • beta decay- atomic no. increases by 1, mass no. stays same
    • tracers- certain chemicals concentrate in diseased/damaged parts of body, radiation concentrates with it. External radiation detectors detect radiation emitted (this + computers build up image of inside the body 
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Waves

  • Waves carry energy, NOT matter
  • Longitudinal waves move in same direction as energy transfer (sound)
  • Transverse waves move perpendicular to direction of energy transfer (light)
  • Equations:-
    • Frequency= 1/ Time period
    • Wave Speed= Frequency x Wavelength
  • All waves can be reflected, refracted and diffracted.       Can be used to carry information.
  • Electromagnetic waves - all travel at 330m/s
  • Analogue and Digital Signals:-
    • analogue signals can vary in frequency, amplitude, or both.
    • digital signals  are a series of pulses consisting of just two states: ON (1) or OFF (0). There are no values in between.
    • ADVANTAGE OF DIGITAL SIGNALS:- carry more info per second, maintin their quality over long distances (better than analogue)
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