2.1 Electricity

• current is the flow of an electrical charge
• potential difference is the work done per unit charge flowing through a component in a circuit
• resistance is the measure of how difficult it is for a current to flow through a component
• the greater the resistance the smaller the current that flows
• charge flow = current X time
• the size of the current is the rate of flow of charge
• potential difference = current X resistance
• ohmic conductors have a constant resistancce
• LDR is short for light dependent resistor, it is a resistor that changes resistance depending on the amount of light
• the resistance of a thermistor depends on temperature
• in a circuit series, components are connected in a line, thats set to end
• series circuit:

  potential difference is shared

  current i the same everywhere

  resistance adds up
• parallel circuits

  each component is separately connected

  potential difference is the same among all components

  current is shared between branches

  adding a resistor in parallel circuits reduces the total resistance
• if you have two resistors in parallel their total resistance is less than the resistance of the smallest two resistors
• mains supply is ac

  battery supply is dc
• in ac supplies, the current is constantly changing

  ac are produced by alternating voltages

  means positive and negative ends keep alternating
• uk mains supply is 230V

  frequency is 50 Hz
• batteries and cells deliver dc

  current flowing in the same direction

  created by direct voltage
• Live wire

  the live wire provides the alternating potential difference (230V) from the mains supply
• Neutral wire - blue

  completes the circuit

  when the appliance is operating normal, current flows through the live and neutral wires, it is around 0V
• earth wire - green and yellow

  stops the appliances from becoming live

  usually does not carry a current

  only when there is a fault
• energy transferred = power X time
• potential difference is energy transferred per charge
• energy transferred = charge flow X potential difference
• power = potential difference = current
• the national grid is a giant web of wires that covers the entire UK
• the national grid uses a high Pd and a low current

  this is transmit lots of energy
• potential difference is changed by a transformer

  step up transformer - pd increased

  step down transformer - pd decreased
• static electricity is all about charges which are not free to move, when they finally move it causes a spark or a shock
• electric fields

  created around any electrically charged object

  the closer the stronger

  the further away the weaker

  they go from positive to negative