Electricity in the Home

• Work is done when charge flows through a circuit

  $Energy \;transferred =$$Power \times Time$ $E=$$Pt$

  • Energy transferred (E) in joules (J)
  • Power (P) in watts (W)
  • Time (t) in seconds (s)
• $E=$$QV$

  • Energy transferred (E) in joules (J)
  • Charge flow (Q) in coulombs (C)
  • Potential difference (V) in volts (V)
• $P=$$VI$

  • Power (P) in watts (W)
  • Potential difference (V) in volts (V)
  • Current (I) in amperes (A)
• $P=$$I^2R$

  • Power (P) in watts (W)
  • Current (I) in amperes (A)
  • Resistance (R) in ohm (Ω)
• Energy is distributed by the national grid which is made up of cables and transformers
• Step up transformers

  • Increase potential and decrease current
  • The low current means that the wires are not transferring thermal energy to the surroundings
  • This is to increase efficiency
• Step down transformers

  • Increase current decrease voltage
  • Decrease the voltage for the safety of the consumers
• Mains electricity is an AC supply ; In the United Kingdom the domestic electricity supply has a frequency of 50 Hz and is about 230 V
• AC is alternating current ; current continuously varies, from positive to negative (charge changes direction)
• DC is direct current ; the movement of charge in one direction only. Cells and batteries supply direct current
• $V_sI_s=$$V_pI_p$​

  • Potential difference across secondary coil (V)
  • Current through secondary coil (A)
  • Potential difference across primary coil (V)
  • Current through primary coil (A)

  
• Neutral Wire

  • Blue, at 0V
  • Completes the circuit
• Live wire

  • Brown, at 230V
  • Carries the alternating potential difference from the supply.
  • This may be dangerous even if mains circuit is off, as current may still be flowing through it
• Earth wire

  o Green and Yellow stripes, at 0V

  o It only carries a current if there is a fault

  o Safety wire to stop the appliance becoming live

  o It is connected to the earth and to the casing

  o If the live wire touches the metal casing of the appliance, it will become live (you’ll get a serious electric shock if you touch it, as current flows through you to the ground)
• Earth wire

  • Green and Yellow stripes, at 0V. It only carries a current if there is a fault
  • Safety wire to stop the appliance becoming live
  • It is connected to the earth and to the casing
  • If the live wire touches the metal casing of the appliance, it will become live (you’ll get a serious electric shock if you touch it, as current flows through you to the ground)