Electricity - Key Terms

• Current


  the flow of electrical charge, measured in amperes (A)
• Charge

  a property of matter that causes it to experience a force when placed in an electric field; electric current is the flow of charge; charge can be positive or negative and is measured in coulombs (C
• Resistance

  a measure of how a component resists (opposes) the flow of electrical charge, measured in ohms (Ω)
• Potential difference

  the difference in electric potential between two points in an electric field; the work that has to be done in transferring a unit of positive charge from one point to another, measured in volts (V)
• Precision

  refers to the degree of accuracy (of a measuring instrument), i.e. the minimum possible change that can be measured
• Ohmic conductor


  a resistor in which the current is directly proportional to the potential difference at a constant temperature
• Diode


  a component that only allows current to flow in one direction (has a very high resistance in the reverse direction)
• Series


  describes a circuit in which the components are connected one after then other, so the same current flows through each component
• Parallel


  a circuit in which the components are connected side by side on a separate branch / path, so that the current from the cell / battery splits with a portion going through each component
• Power


  a measure of the rate at which energy is transferred or work is done
• Direct current (d.c.)

  a continuous electric current that flows in one direction only, without significant variation in magnitude, e.g. the current supplied by cells and batteries
• Alternating current (a.c.)


  a continuous electric current that periodically reverses direction, e.g. mains electricity in the UK
• Electrical potential

  the potential difference between the point and some other reference point
• Power


  a measure of the rate at which energy is transferred or work is done
• Efficiency


  the ratio or percentage of useful energy out compared to total energy in for a system or device
• National Grid


  the network of high voltage power lines and transformers that connects major power stations, businesses and homes
• Transformer

  a device that transfers an alternating current from one circuit to another, with an increase (step-up transformer) or decrease (step-down transformer) of voltage
• Isolated


  refers to an object that has no conducting path to earth
• Spark

  a momentary flash of light accompanied by a sharp crackling noise, produced by a sudden electrical discharge through the air between two points
• Attraction


  a force by which one object attracts ('pulls') another, e.g. gravitational or electrostatic force
• Repulsion


  a force that pushes two objects apart, such as the force between two like electric charges or magnetic poles