P5 Electricity Flashcards
What is alternating current
An electric current in a circuit that repeatedly reverses its direction
What is direct current
An electric current in a circuit that is in one direction only
What is an earth wire
The wire in a mains cable used to connect the metal case of an appliance to earth
What is a fuse
A fuse contains a thin wire that melts and cuts the current off if too much current passes through it
What is a live wire
The mains wire that has a voltage that alternates in voltage
What is the alternating voltage of live wires in Europe
+325V and -325V
What is a neutral wire
The wire of a mains circuit that is earthed at the local substation, so its potential is close to zero
What is an oscilloscope
A device used to display the shape of an electrical wave
What is a plug
A plug has an insulated case and is used to connect the cable from an appliance to a socket
What is a step-down transformer
An electrical device used to step-down the size of an alternating potential difference
National grid => consumers
What is a step-up transformer
An electrical device used to step-up the size of an alternating potential difference
Power station => national grid
What produces direct current
Cells
Batteries
What produces alternating current
Generators
What uses direct current
Electronic circuits
What uses alternating current
Mains electricity
Motors
Can direct current be efficiently transferred over long distances
No
Can alternating current be efficiently transferred over long distances
Yes
How are hertz calculated
cycles / second
What is the alternating p.d produced by power stations
~25,000V
What is the frequency of mains electricity in the UK
~50Hz
What is the voltage of mains electricity in the UK
230V
What changes AC to DC
A rectifier
E.g. a diode
These components only allow current to flow in one direction
How is hertz calculated using cycle time
Hz(ac) = 1 / time(cycle)
How is peak wattage calculated
W(peak) = 2W(stated)
bc W(stated) = W(average)
How is P(av) calculated
(current(max) * voltage(max)) / 2 OR wattage(max) / 2
