Definitions

• Alternating current

  In an alternating current (AC), electrons oscillate backwards and forwards around a mean position, as opposed to direct current (DC). Household power supplies usually operate at 240 V AC.
• Ammeter

  An instrument for measuring either direct (DC) or alternating electric current, in amperes.
• Charge

  A property of matter that causes electric effects. Protons have positive charge, electrons have negative charge and neutrons have no charge.
• Circuit breaker

  A device that automatically switches off an excessive current by detecting the magnetic field associated with it.
• Conductor

  A substance, body or system that readily conducts heat, electricity, sound or light.
• Convection current

  A flow of positive electric charge. Conventional current is in the opposite direction to electric flow.
• Coulomb

  The SI unit of charge; 1C is equivalent to the combined charge of 6.2 x 10^18 protons.
• Current

  The net flow of electric charge. Current is measured in amperes (A) where 1 A = 1 C s-1. By convection, electric current is assumed to flow from positive to negative.
• Direct current

  In a direct current (DC), electrons travel one direction only, as opposed to alternating current (AC). Batteries and electric cells provide direct current.
• Earth

  The third wire (usually green or green and yellow) in electric devices that acts as an important safety feature by carrying excess current due to a device malfunction directly into the Earth.
• Effective resistance

  A single resistance that could be used to replace a number of individual resistors for the purpose of circuit analysis.
• Electric current

  The flow of charged particles.
• Electric shock

  Also known as electrocution, in which excess electricity flows into the human body due to a device malfunction or electrical accident.
• Electrical potential energy

  Potential energy due to the separation of charge in part of an electric current.
• Electricity

  A form of energy resulting from the existence of charged particles (electrons or protons). Electricity is fuelled by the attraction of particles with opposite charges and the repulsion of particles with the same charge.
• Electron flow

  The net flow of electrons. Although electric current is assumed to flow from positive to negative, electrons physically move from negative to positive.
• Elementary charge

  The magnitude of the charge on an electron or proton: e = 1.6 x 10^-29 C.
• Fuse

  A circuit device that melts when too much current flows through it, breaking the circuit and protecting the other circuit components.
• Insulators

  A material or an object that does not easily allow heat, electricity, light or sound to pass through it. Air, cloth and rubber are good electrical insulators; feathers and wool are good thermal insulators.
• Ion

  Atom of a chemical element in which the number of electrons and protons are not equal and therefore the atom is electrically charged. If extra electrons are present, the ion has a negative charge. Is electrons are missing , the ion has a positive charge.
• Junction

  A point in an electric circuit from which current can flow in or out in more than one direction.
• Kilowatt hour (kWh)

  Unit of energy equivalent amount of energy to 3.6 megajoules. The equivalent amount of energy to that used by a 1000 W device turned on for one hour. It is the unit of measure of electricity usage that is measured by electricity meters and appears on electricity bills.
• Metal

  Material in which some of the electrons are only loosely attracted to their atomic nuclei. The properties of metal include: high strength, good electrical and thermal conductivity, lustre, malleability and ductility.
• Net charge

  When the number of positive and negative charges in an object is not balanced.
• Non-metal

  Material in which all of the electrons are strongly attracted to their atomic nuclei.
• Non-ohmic

  Not behaving according to ohm’s law; resistance charges depending on the potential difference.
• Ohmic

  A resistor that follows Ohm’s law, i.e. Has a linear relationship between the current it draws and the potential difference across it.
• Overload

  When an unsafe amount of current flows though a wire; for example, when too many electrical appliances are connected to the same powerpoint.
• Parallel circuit

  A circuit that contains junctions; the current drawn from the battery, cell or electricity supply splits before it reaches the components and re-joins afterwards.
• Potential difference

  The difference in electric potential between two points in a circuit; measured by a voltmeter when placed across a circuit. A battery creates the potential difference across a circuit, which drives the current.
• Power

  The rate at which work is done; a scalar quantity measured in watts (W).
• Resistance

  A measure of how much an object or material resists the flow of current; the ratio of the potential difference across a circuit component an the current flowing through it: R = V/I. resistance is measured in ohms (Ω).
• Resistor

  A circuit component, often used to control the amount of current in a circuit by providing a constant resistance. Resistors are ohmic conductors, i.e. they obey Ohm's law
• Residual current device

  A device that can detect a difference in the active and neutral wires and switch off current in dangerous situations to help prevent electrocution.
• Series circuit

  When circuit components are connected one after another in a continuous loop so that the same current passes through each component.
• Short circuit

  The situation in which good conductor is inadvertently placed across a battery and an excessive current flows, which may cause damage.
• Transfer

  The conversion of energy from one system to another.
• Transform

  To change from one form to another; for example, to change energy from electrical potential energy to kinetic energy.
• Voltmeter

  A device used to measure the electrical potential difference between two points in a circuit.
• Volt

  The unit of electrical potential. One volt is equal to one joule of potential energy given to one coulomb of charge in a source of potential difference. The voltage (or the number of volts) in another name for the potential difference.