electricity

• current 


  rate of flow of charge
• units of current 


  ampres (A) or amps
• charge equation


  Q= It
• current is measured using...

  ammeter, connected in series
• potential difference / voltage 


  the work done per unit charge
• units of p.d 


  volts (V)
• p.d equation 


  V = W / Q
• p.d is measured using...

  voltmeter, connected in parallel
• resistance 


  the hinderance to the rate of flow of charge
• for a given p.d, the higher the resistance...


  the lower the current
• good conductors have...


  low electrical resistance
• resistance equation


  R = V / I
• units of resistance 


  ohms
• a higher resistance means ...


  smaller current
• a lower resistance means ...


  a larger current
• ohms law states...

  for a conductor at constant temperature, the current is directly proportional to the p.d
• ohms law equation 


  V = IR
• an electrical component obeys ohms law if...

  • the graph of I - V is a straight line through the origin
  • a resistor obeys ohms law
  • filament lamp does not obey ohms law
• I-V characteristics - as the p.d is increased ...


  the current also increases (ohms law)
• for an ohmic conductor ... (I-V graph)

  the I-V graph is a straight line through origin
• for semiconductor diode... (I-V graph)


  the I-V graph is a horizontal line that goes sharply upwards
• for filament lamp ... (I-V graph)

  the I-V graph has a 'S' shaped curve
• ohmic conductor

  • the current is directly proportional to the p.d
  • demonstrated through the straight line through origin
• semiconductor diode

  • diode used in a circuit to allow current to flow only in a specific direction
  • When the current is in the direction of the arrowhead symbol, this is forward bias. This is shown by the sharp increase in potential difference and current on the right side of the graph
  • When the diode is switched around, it does not conduct and is called reverse bias. This is shown by a zero reading of current or potential difference on the left side of the graph