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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 769862292 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. 769862292