electricity

• current 


  is the flow of electric charge units= ampere
• potential difference 


  (Voltage) is the driving force that pushes charge round the circuit
• Resistance 


  Anything in the circuit which slows the flow down

  Units = ohms
• circuit symbols 


  =

  
• Investigating Resistance


  1. Attach crocodile clip to wire at 0cm

  2. Attach second crocodile clip to wire, e.g. 10cm away

  3. Close switch, record current and potential difference

  4. Open switch, move second clip, e.g. another 10cm, close switch, record new length, current and potential difference

  5. Repeat for a number of different wire lengths
• Ammeter


  • Measures the current (in amps) flowing through the test wire
  • Must always be placed in series with whatever you're investigating
• Voltmeter


  • Measures the potential difference (or pd) across the test wire (in volts)
  • Must always be placed in parallel around whatever you're investigating, not around any other bit of the circuit
• Resistance is directly proportional to wire length


  The longer the wire, the greater the resistance
• Ohmic conductor


  • Has an I-V characteristic that's a straight line
• Non-linear components (e.g. filament lamp, diode)


  • Have a curved I-V characteristic
• To find a component's I-V characteristic

  1. Set up the test circuit

  2. Vary the variable resistor to alter the current flowing through the circuit and the potential difference across the component

  3. Take several pairs of readings from the ammeter and voltmeter

  4. Reverse the direction of the current

  5. Plot a graph of current against voltage for the component
• 1. I-V characteristics

  • Ohmic conductor
  • Filament lamp
  • Diode
• Ohmic conductor


  The current through it is directly proportional to the potential difference, so the I-V characteristic is a straight line
• Filament lamp


  As the current increases, the temperature of the filament increases, so the resistance increases. This means less current can flow per unit pd, so the I-V characteristic gets shallower and curves
• Diode


  Current will only flow through it in one direction. It has very high resistance in the reverse direction.
• Thermistor 


  Is a temperature dependent resistor

  -resistance decreases as temperature increases
• LDR (light- dependent resistor)


  bright light = resistance falls

  darkness = resistance is high
• series circuit

  • current is the same everywhere
  • total resistance adds up over components
  • cell potential difference adds up
  • total potential difference is shared
• Parallel circuit


  Potential difference is the same across all components

  Current is shared between branches

  adding a resistor in parallel reduces total resistance
• Adding Resistors in Series

  1. Find at least four identical resistors

  2. Build the circuit shown using one resistor

  3. Measure the potential difference of the battery

  4. Measure the current through the circuit

  5. Calculate the resistance of the circuit using R=V/I

  6. Add another resistor in series

  7. Measure the current and calculate the overall resistance

  8. Repeat until all resistors are added

  9. Plot a graph of number of resistors against total resistance
• Adding resistors in series


  • Increases the total resistance of the circuit (adding a resistor decreases the total current through the circuit)
• Adding more resistors


  • The larger the resistance of the whole circuit
• Adding resistors in parallel


  • The total current through the circuit has the smaller the overall resistance of the circuit
• Neutral wire 


  BLUE

  completes the circuit when the appliance is operating normally current flows through the live and neutral wires it is around 0V
• live wire 


  BROWN

  the live wire provides the alternating potential difference at about 230V from the main supply
• Earth wire


  GREEN AND YELLOW

  protecting the wiring and for safety

  0volts
• The national grid 


  A giant system of cables and transformers that covers the uk and connects power stations to consumers
• charges 


  Like charges repel

  opposite charges attract