chapter 9: electrical circuits

ammeter

A device used to measure electric current — it must be placed in series and ideally have zero resistance

diode

A semiconductor component that allows current only in one particular direction

efficiency

The ratio of useful output energy to total input energy

electricity meter

A device that measures the electrical energy supplied in kWh to a house from the grid

electromotive force (e.m.f.)

The work done on the charge carriers per unit charge

electronvolt

A derived unit of energy used for subatomic particles and photons

filament lamp

An electrical component containing a narrow filament of wire that transfers electrical energy into heat and light

internal resistance

The resistance of a source of e.m.f. (e.g a cell) due to its construction

I–V characteristic

A description of the relationship between the electric current in a component and the potential difference across it — in most cases this is usually in the form of a simple graph of I against V

kilowatt-hour

A derived unit of energy

light-dependent resistor

An electrical component with a resistance that decreases as the light intensity incident on it increases

light-emitting diode

A type of diode that emits light when it conducts electricity

loading (electrical circuits)

Connecting a component or a device across the terminals of a source of e.m.f. or across another component

lost volts

The potential difference across the internal resistor of a source of e.m.f.

negative temperature coefficient (NTC)

A relationship in which a variable decreases as temperature increases

non-ohmic component

A component that does not obey Ohm’s law

ohm

The derived SI unit of resistance

Ohm’s law

The potential difference across a conductor is directly proportional to the current in the component as long as its temperature remains constant

ohmic conductor

A conductor that obeys Ohm’s law

oscilloscope

An instrument that displays an electrical signal as a voltage against time trace on a screen

parallel circuit

A type of branching electrical circuit in which there is more than one path for the current — components in parallel have the same potential difference

polarity

The type of charge (positive or negative) or the orientation of a cell relative to a component

potential difference (pd)

Defined as the energy transferred from electrical energy to other forms (heat

potential divider

An electrical circuit designed to divide the potential difference across two or more components (often two resistors) in order to produce a specific output

potential divider equation

An equation relating the output potential difference from a simple potential divider containing a pair of resistors:   in out x V R R R V 2 1 2  

potentiometer

An electrical component with three terminals and some form of sliding contact that can be adjusted to vary the potential difference between two of the terminals

power

The rate of work done

resistance

A property of a component calculated by dividing the potential difference across it by the current in it

resistivity

A property of a material

resistor

An electrical component that obeys Ohm’s law

resistor circuit

Two or more resistors arranged to provide a specific resistance

series

An arrangement of electrical components connected end-to-end that means that the current is the same in each component

series circuit

A type of electrical circuit where the components are connected end-to-end

superconductivity

A phenomenon in which the resistivity of a material falls to almost zero when the material is cooled below a certain temperature

terminal p.d.

The potential difference across an electrical power source — when there is no current this is equal to the e.m.f. of the source

thermistor

An electrical component that has a resistance that decreases as the temperature increases (a negative temperature coefficient)

threshold voltage

The minimum potential difference at which a diode begins to conduct

timebase

The time interval represented by one horizontal square on an oscilloscope screen

volt

The derived SI unit of potential difference and electromotive force

voltage

See ‘potential difference’

voltmeter

A device used to measure potential difference — it must be placed in parallel across components and ideally have an infinite resistance