Topic 10: Electricity

• Series Circuit:

  • dim light
  • same current throughout
  • voltage shared between components
  • increased resistance (sum)
• Parallel Circuit:

  • bright light
  • same voltage throughout
  • current splits between junctions
  • decreased resistance (no sum)
• Potential Difference (Voltage) - driving force that pushes the charge around and is measured by a voltmeter in volts (V)
• Current - flow of electric charge and is measured by an ammeter in amps/amperes (A)
• Resistance - anything that slows the flow, is measured in ohms (Ω) and can be controlled/caused by a (variable) resistor
• Fixed Resistor - In its graph, V=I as long as the temperature and resistance doesn't change (remains constant)

  
• Filament Lamp - curves as the bulb is heating up, therefore the resistance increases so its not proportional to the current

  
• Diode - allows current to only flow through one direction so there is no current backwards

  
• LDR (Light-Dependent Resistor) - there is a negative correlation between light intensity and resistance so its used for phones/street lamps

  
• Thermistor - has a negative correlation between resistance and temperature so its used for kettles/cooling systems

  
• Particle vibrations create heat and resistance:

  • electrons collide with vibrating ions and slow down
  • energy transferred to ions which then vibrate faster and create heat
  • electrons work against resistance so thermal energy dissipates
  • low resistance wires or super cooling can reduce heat loss
  • can be an advantage (toaster) and disadvantage (chargers)
• Alternating Current - AC has changing potential difference, 50Hz and 230V (mains supply)

  
• Direct Current - either positive or negative, charge always flowing in the same direction, cells/batteries and current flows from positive to negative

  
• Fuses - a very thin piece of wire that melts when heated up
• Fuses break circuits so no more current can flow for safety:

  • simple (advantage)
  • cheap (advantage)
  • permanently broken after a single surge to not damage the appliance (disadvantage)
• Neutral Wire - completes the circuit by carrying away current, 0V

  Live Wire - carries AC current, 230V

  Earth Wire - provides alternate pathway for current to flow away, doesn't normally carry a current, stops appliance casing from becoming live (electrical shocks), 0V

  
• Earthing - if a live wire touches a metal case, a large current flows from the live wire to the earth wire which breaks the fuse and carries the current into the soil