# IGCSE Electricity definitions

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DULWICH COLLEGE SHANGHAI

IGCSE ELECTRICITY DEFINITIONS AND CONCEPTS
ELECTRIC CHARGE (Q): The cause of electric fields and currents. Either positive
or negative. Q=It

ELECTRICAL CONDUCTOR: A material which allows electric charge to flow

ELECTRICAL INSULATOR: A material which prevents the flow of electric charge.

EARTHING: The connection of a conductor to the earth which allows electric
charge to flow.

ELECTRIC FIELD: The space around an electric charge in which another charge
will experience a force.

ELECTRIC CURRENT (I): The flow of electric charge.

AMPERE (A): The unit of electric current.

COULOMB (C): The unit of electric charge. When a current of 1A flows for 1s, 1C
passes.

DIRECT CURRENT: An electric current where the electrons flow in the same
direction all the time (conventional current flows from + to -). A battery delivers
DC.

ALTERNATING CURRENT: An electric current which is constantly changing
direction of its flow. The mains supply is AC.

AMMETER: An instrument which measures electric current. It must be
connected in series with the current it is measuring.

SERIES: Components connected end to end in a chain.
PARALLEL: Components connected in a ladder formation.

KIRCHHOFF’S LAW: The current flowing into any point in a circuit is equal to the
current flowing out of it.

JOULE (J): Unit of energy.

WATT (W): Unit of power. 1W = 1J/s

POTENTIAL DIFFERENCE (V): When a source builds up an excess of electrons at
the negative terminal, it is said to have a potential difference across its terminals
(ie a current would flow if there were a circuit connection). It is also known as
voltage and is a measure of energy transferred per coulomb. flowing between
two points.

VOLT (V): When 1 coulomb passes between two points and transfers 1 joule of
energy, the potential difference between the points is 1 volt. 1V=1J/C.
PD=Energy/Charge

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DULWICH COLLEGE SHANGHAI

VOLTMETER: An instrument which measures the potential difference between
two points. It must be connected in parallel with the PD it is measuring.

EMF: The maximum voltage of a source. How many joules per coulomb it can
transfer.

RESISTANCE (R): The amount that a component resists the flow of current.
R=V/I

OHM (Ω): the resistance of a conductor where the current is 1 A when a PD of 1V
is across it.

OHM’S LAW: The current through a metallic conductor is directly proportional to
the voltage across its ends if the temperature and other conditions are constant.

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