electricity (pape1 phys)

• Electrical circuit


  A closed loop that contains a power source such as a cell and something for the electrons to flow through like a wire
• Circuit diagram


  • Represents an electrical circuit
• Main circuit components


  • Cell/battery
  • Filament lamp
  • Switch
• Cell


  A simple version of a battery, which is made up of two or more cells
• Filament lamp


  A small light bulb
• Switch


  Can be closed allowing current to continue flowing around the circuit or open which would disrupt the circuit
• v = ir


  Potential difference or voltage equals current times resistance
• As voltage increases


  Current increases proportionally
• As voltage decreases


  Current decreases proportionally
• Circuits with only wires or resistors

  • Resistance stays constant
  • Resulting in straight line graphs of current vs potential difference
• Larger resistor

  Line on current vs potential difference graph is less steep
• Current (I)

  A measure of the flow of electrons around the circuit, similar to the flow of water through a pipe, measured in amperes (amps)
• Smaller resistor

  Line on current vs potential difference graph is steeper
• Higher currents can cause wires to heat up, so lines on graphs don't always look perfectly straight
• Filament lamps


  • Contain a very thin metal filament
  • As current flows, filament heats up and resistance increases
  • Resulting in a curve on the current vs potential difference graph that gets less steep at higher voltages
• Diodes


  • Only allow current to flow in one direction
  • Have a very high resistance in the reverse direction
• Potential difference (V)


  The force driving the flow of electrons, provided by the cell or battery, also known as voltage, measured in volts
• Diodes only show current when the potential difference is positive
• Resistance (R)


  Everything that resists or opposes the flow of electrons, similar to a partial blockage in a pipe, measured in ohms
• National grid


  Giant network of transformers and wires that spreads across the country to distribute electricity
• Sources of electricity generation in the UK

  • Fossil fuels
  • Nuclear fission
• How power stations generate electricity

  1. Generate heat

  2. Convert thermal energy into electrical energy
• Electricity demand


  Peaks in the late afternoon and evening
• Spare capacity


  Power stations need to have lots of spare capacity to cope with surges in demand
• Power stations often run at well below their maximum power output regardless of the time of day
• Power


  Voltage times current
• High current flowing through a wire generates lots of heat due to resistance, causing energy loss
• Step-up transformers


  Increase the voltage to around 400,000 volts before sending electricity across the country
• Electrons flow from the negative terminal to the positive terminal of a cell or battery
• Conventional current is said to flow from the positive terminal to the negative terminal, even though it's opposite to the actual electron flow
• Step-down transformers


  Lower the voltage back down to around 230 volts before it reaches its destination
• High voltages are dangerous and would blow appliances in our houses
• series circuits

  • total p.d is shared between all components
  • current is the same as all components
  • total resistance= sum of resistance
• parallel circuits

  • p.d for each branch= p. for all cells/batteries
  • current is split between the branches
  • adding mire resistors in parallel reduces total R
• neutral wire - blue

  live wire - brown

  earth wire- yellow and green