# IGCSE Electricity

 What name is given to current that only flows in one direction? Direct current (dc) What sort of current is supplied by cells and batteries? Direct current (dc) What do the letters a.c. represent? Alternating current What is the period of an ac wave? The time for a complete cycle What is the relationship between the frequency (f) and the time period (T) of an ac wave? (T in seconds, f in Hz) What names are given to the three wires in a UK mains plug? LiveNeutralEarth Some mains cables only have two wires. Which wire is missing? Earth Which one of the 3 mains wires are circuit breakers and fuses always connected into? Live What happens to a fuse if the current exceeds the rating of the fuse? It melts, thereby breaking the circuit Which acts the fastest, a fuse or a circuit breaker? circuit breaker Which appliances are usually earthed? Those with metal cases What is the purpose of the earth wire? By providing a low-resistance path for the current to flow in the event of a fault, it enables the fuse to blow and break the circuit What happens when an electrical charge flows through a resistor? It gets hot In a filament lamp, what is most of the electrical energy converted into? Heat (wasted) What is the unit of power? Watt (W) What is the unit of energy? Joule (J) What is the unit of electrical current? Amperes (Amps) (A) What is the unit of electrical charge? Coulomb (C) What is the relationship between energy (E), potential difference (V) , and charge (Q) E = V x Q Are electrons negatively or positively charged? Negatively What causes some insulating materials to become electrically charged when they are rubbed together? Electrons are rubbed off one material and onto the other What happens when two electrically charged objects (that have the same charge) are brought together? They repel each other Give an example of a type of material that electrical charges can move through easily Metals What is electric current? A flow of electric charge What is the unit of electrical current? Ampere (Amp) (A) How is the size of a current (I) calculated from the total charge (Q) and time (t)? I = Q/t What is the standard unit of electrical charge? Coulomb (C) What is potential difference another name for ? Voltage What component is this graph for? Resistor What is the unit of resistance? Ohm If a component has a larger resistance, will the current be larger or smaller? Smaller In a series circuit, what do you know about the current at different points? It is always the same In a series circuit how is the total resistance calculated? By adding up the individual resistances For components connected in parallel what do you know about the potential difference across each component? They are all the same What component is this graph for? Filament bulb Which component only allows current to flow one way? Diode What component is this graph for? Diode What happens to the resistance of an LDR as light intensity increases? The resistance decreases What happens to the resistance of a thermistor as temperature increases? The resistance decreases Which component emits light when a current flows through it in a forward direction? Light Emitting Diode (LED) AuthorSilcoatesScience ID300259 Card SetIGCSE Electricity DescriptionIGCSE Electricity Updated2015-04-08T15:15:52Z Show Answers