# mains electricity

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• Created by: Abi14
• Created on: 18-04-14 11:23
what is direct current?
is in one direction only. cells and batteries
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what is alternating current?
current that repeatedly reverses its direction. supply from mains.
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what is the frequency of theUK mains supply?
50 hertx (Hz), this means it is changing directions 50 times per second.
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what is the voltage of the UK mains supply?
230 volts
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what does the live wire do?
alternates between peak voltage of +325V and -325V. in terms of electrical power, this is equivlent to a direct potential difference of 230V
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what is the equation fr frequency?
the frequency of an ac supply can be determined from an oscilloscope trace using an equation -----> f=1/T f= frequency of sc in hertz T= time for one cycle in seconds.
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why is the outer cover of a plug made of platic or rubber?
good electrical insulator
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why are the pins in a plug made from brass?
brass is a good conductor. it is also hard and will not rust or oxidise.
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what are the plugs casing if an earth wire is needed?
metal case. appliances with plastic cases do not need an earth wire. they are said to be double insulated and are connected t the supply with two-core cable containing just a live and neutral wire.
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what should the earth wire be connected to?
the longest pin
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what should the brown wire be connected to?
the live pin
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what should the blue wire be connected to?
the neutral pin
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what does the cable grip do?
it is importqant that the cable grip is fastened tightly over the cable. there should be no bare wires showing inside the plug and the correct cable must be connected firmly to the terminal of the correct pins.
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how can the wire thickness affect the appliance it is used for?
cables of different thickness are used for different purposes. the more current to be carried, the thicker the cable needs to be.
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why dont plastic cases on a plug need a earth wire?
because plastic is an insulator and therefore can not become live.
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why do metal cases on a plug need an earth wire?
otherwise if a fault develops, and the live wire touches the metal case, the case becomes live and could give a shock to anyone who touches it.
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what is a fuse?
a fuse is always fitted in series with a live wire. this cuts the appliance off from the live wire if the fuse blows.
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what happens if a fault occurs in an earthed appliance?
a large current flows to the earth and melts the fuse, disconnecting the supply.
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what should the rating of the fuse be>
should be slightly higher than the normal working current of an appliance. if it is much higher, it will not melt soon enough. if it is not high enough than normal current, it will melt as soon as the appliance is switched on.
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what is a circuit breaker?
can be used in placce of a fuse. this is an electromagnetic switch that opens and cuts off the supply if the current is bigger than a certain value.
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what does a residual circuit breaker do?
cuts off the current in the live wire if its different to the circuit in the neutral wire. it works faster than a fuse or an ordinary circuit breaker.
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what is power?
an electrical appliance transfers electrical energy into other forms of energy. the rate at which it does this is called the power.
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what is the equation for power?
P=E/t P= power in watts W E=energy transfer in Joules J t=time in seconds
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what is the equation that uses potential difference and current to work out the amount of power?
P= I X V *P=power in watts I=current in Amps V= potential difference in volts.
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what is the eletrical current?
is the rate of flow of charge
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what is the equation for charge?
Q=I X t * Q= charge in coulombs I= current in amps t= time in seconds
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what happens when charge flows through an appliance?
when charge flows through an appliance, electrical energy is transferred to other forms. in a resistor, electrical energy is transferred to the resistor so the resistor becomes hotter.
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what is the equation for energy?
E= V X Q * E= energy transfer in Joules V= potential difference in Volts Q = charge in coulombs
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why may electrical faults occur?
as a result of damage to socket, plugs, cable or appliance.
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## Other cards in this set

### Card 2

#### Front

what is alternating current?

#### Back

current that repeatedly reverses its direction. supply from mains.

### Card 3

#### Front

what is the frequency of theUK mains supply?

### Card 4

#### Front

what is the voltage of the UK mains supply?

### Card 5

#### Front

what does the live wire do?