electricity

• Current


  The rate of flow of charge at a point in the circuit, measured in amperes (A)
• Potential difference


  The work done per unit charge in moving between two points in a circuit, measured in volts (V)
• Resistance


  The measure of how hard it is for current to flow through a component, measured in ohms (Ω)
• Ohmic conductor


  • Current is directly proportional to voltage (constant resistance)

  
• Non-ohmic conductor


  • Resistance changes as voltage and current change

  
• Thermistor


  A resistor whose resistance decreases as temperature increases
• Light dependent resistor


  A resistor whose resistance decreases as light intensity increases
• Series circuit


  1. Components connected end to end in one loop

  2. Same current flows through every component

  3. Potential difference is shared across each component
• Parallel circuit


  1. Components connected to power supply in separate branches

  2. Current is shared between each branch

  3. Potential difference is the same across every branch
• Damaged insulation can cause electric shock or fire hazard
• Overheating of cables can melt insulation and cause fire
• Damp conditions can conduct current and cause electric shock
• Fuse


  A thin piece of wire that overheats and melts if current is too high, protecting the circuit
• Circuit breaker


  An automatic electromagnet switch that breaks the circuit if current rises over a certain value
• Earth wire


  Creates a safe route for current to flow through in case of short circuit, preventing electric shocks
• Double insulation


  Appliances have plastic casings or are designed so earth wire cannot touch metal casing, preventing electric shock
• Energy


  Measured in joules (J), transferred from chemical energy in battery to electrical energy used by circuit components and then to surroundings
• Power


  Measured in watts (W), the rate of energy transfer
• Direct current


  Current only flows in one direction
• Alternating current

  Current continuously changes direction
• Charge


  Measured in coulombs (C), there are positive and negative charges that attract and repel
• Atoms


  • Composed of protons (+1), electrons (-1), and neutrons (0)
• Conductors


  Allow electrons to flow through them
• Insulators


  Impede the flow of electrons
• Charging by friction


  Electrons transfer from one insulator to another, creating positive and negative charges
• Consequences of static electricity


  • Lightning
  • Charged balloon on wall
  • Comb picking up bits of paper
• Static charges pose risk of electric shock
• Static charges can ignite fuel and cause fire or explosion
• Earthing


  Offering electrons an alternative pathway to the earth to prevent too much electrostatic charge building up
• Uses of electrostatic charges


  • Inkjet printer
  • Photocopier