definitions and concepts

• ammeter

  a device that measures the current in the loop of the circuit that it is connected in series with

  • an ideal ammeter is modelled to have zero resistance
• current

  the rate of flow of charge in a circuit
• electromotive force

  the amount of energy transferred by a source to each unit of charge that passes through it
• internal resistance

  the resistance to the flow of charge within a source

  • internal resistance results in energy being dissipated within the source
• light dependent resistor

  a light sensitive semiconductor whose resistance increases when light intensity decreases
• ohmic conductor

  a conductor for which the current flow is directly proportional to the potential difference across it when under constant physical conditions

  • perfectly obeys ohm's law
• ohm's law

  the current and potential difference through an ohmic conductor held under constant physical conditions are directly proportional, with resistance being the constant of proportionality
• parallel circuits

  components are said to be parallel when they are connected across each other in separate loops
• potential divider

  a method of splitting a potential difference by connecting two resistors in series

  • the total potential difference is split in the ratio of their resistances
• resistance

  a measure of how difficult it is for current to flow through a material
• resistivity

  a quantity that is proportional to an object's resistance and cross-sectional area, and is inversely proportional the object's length
• resistors in parallel

  • the potential difference is identical for each resistor
  • the current is split between the resistors
  • the total resistance is equal to the inverse of the sum of the inverses of the resistances of the resistors
• resistors in series

  the current through resistors is identical for each resistor

  the potential difference is split in the ratio of their resistances

  the total resistance is equal to the sum of the resistance of the resistors
• series circuits

  when components are connected end to end in one loop
• superconductor

  a material which has zero resistivity when the temperature is decreased to, or below, the material's critical temperature

  • superconductors can be used to produce strong magnetic fields and reduce energy loss when transmitting electric power
• terminal potential difference

  the potential difference across the terminals of a power source

  • equal to the source's emf minus any voltage drop over the source's internal resistance
• thermistor

  a temperature sensitive semiconductor whose resistance increases when temperature decreases
• voltmeter

  a device used to measure the potential difference across components

  • an ideal voltmeter is modelled to have infinite resistance