Day 113


  • Rate at which charge flows through a surface I=Q/t, where I=current;Q=charge; t= time
  • I is measured in Amperes (A) = 1C/s
  • Analogy: rate at which blood flows through a vein or artery
  • Current direction convention is to give the current flow the same direction as the flow of positive charges Therefore, current flows from the positive to the negative terminal of a battery


  • The battery provides the emf in the circuit
  • Emf = electromotive force; another term for potential difference or voltage; measured in Volts (V)
  • Analogy: the heart provides the flow of blood just as the battery provides the flow rate of charges (current) in the circuit
  • The heart/artery/vein system is a closed system just like an electric circuit


  • Provides a deterrent to the flow of current in the circuit
  • Resistors are used to reduce the amount of current
  • At a constant voltage, R and I are inversely related
  • Analogy: Plaque build-up in the artery inhibits blood flow
  • Resistors can be fixed or variable in a circuit
  • Examples of appliances with variable resistors: toaster, iron, hairdryer. Resistance occurs because the electrons are restricted by the walls of the wires