P10 electricity

• Ammeter


  How it is connected in a circuit
• ammeter meausres current in amperes,A
• Electric current


  What causes it in metals
• Electric current


  Units of measurement
• Electron flow


  Direction in a circuit
• Conventional current


  Direction in a circuit
• Equation linking charge, time and current


  Charge (C) = current (A) x time (s)
• Source of potential difference in a closed circuit


  There will be a current in the circuit
• Resistance increases in a circuit


  Current decreases
• Resistance decreases in a circuit


  Current increases
• Changing resistance in a circuit

  Putting different resistors in the circuit or by using a variable resistor
• Equation linking resistance, potential difference and current

  Potential difference (V) = current (A) x resistance (ohms)
• Resistors connected in series

  Net resistance increases
• Resistors connected in series

  Current pathway becomes harder to flow through
• Resistors connected in parallel

  Net resistance decreases
• Resistors connected in parallel

  There are now more paths for the current
• Light intensity increases for an LDR


  Resistance decreases
• Temperature increases for a thermistor


  Resistance decreases
• Current in a resistor

  There is an energy transfer which heats the resistor
• Current against electrical resistance

  Electrical energy is dissipated as thermal energy in the surroundings
• Thermal energy in circuits

  Collisions between electrons and the ions in the lattice
• Power


  The energy transferred per second
• Equation linking energy transferred, power and time taken

  Power (W) = energy transferred (J) / time taken (s)
• Power transfer in any circuit device

  Related to the potential difference across it and the current in it
• Equation linking power, potential difference and current


  Power (W) = current (A) x potential difference (V)
• Equation linking current, power and resistance


  Power (W) = current squared (A^2) x resistance (ohm)
• Direct current


  Movement of charge in one direction only
• Sources of direct current

  • Cells and batteries
• Alternating current


  Current where the movement of charge changes direction
• The domestic supply in the UK is alternating current
• Frequency of UK domestic electricity supply

  50 Hz
• Potential difference of UK domestic electricity supply

  About 230 V
• Live wire function


  Connects the appliance to the generators at the power station
• Neutral wire function


  It is the return path to the power station
• Earth wire function


  For safety
• Potential difference of live wire

  230 V
• Potential difference of neutral wire

  0 V
• Potential difference of earth wire

  0 V
• Where switches and fuses should be connected

  Live wire
• How fuses work


  If the current is too high, the wire inside the fuse will melt, breaking the circuit