cables and transformers

• Earth wire - safety - prevents shock and fire, 0v unless there is a problem

  
• Neutral wire - at or close to 0v

  
• Live wire - AC, alternatives between high +ve and -ve voltage ( 230V). Wire and pins are metal because metals are good conductors. This is because they have delocalised electrons. Plug cases and other insulators are plastic because they do not conduct electricity.

  
• Batteries voltage depends on battery size, does not change direction
• Direct current graph for a battery

  
• Direct current graph for a dynamo

  
• Alternating current maintains electricity. 230, 50Hz. Alternates between high and low voltage and changes direction.

  
• Transformers change potential difference
• Step up transformers increase the potential difference and decrease the current so it is more efficient. ( less thermal energy is wasted from resistance in the wire )
• Step down transformers decrease the voltage and increase the current so the voltage is 230V for the home so it is at safe levels.
• Power lines and substations are potentially dangerous as an electric shock can kill someone who gets too close to such a high voltage supply.
• Work done is energy transferred
• Work is done when charge flows in a circuit
• Power is the rate at which work is done
• Current is the rate of flow of charge around a circuit
• Electrons are the charge