10. P5 Mains Electricity Flashcards
What is meant by the frequency of an AC supply?
The number of cycles per second.
What is the frequency of mains electricity in the uk?
50 Hz (50 cycles per second)
What two wires do every device connected to the mains have?
Live wire and neutral wire
What type of current is the mains electricity?
A.C. (alternating current)
Potential Difference of the mains supply?
230 V
Maximum value that the PD reaches in the mains supply of the UK?
325V
What type of current is produced by a battery?
Direct current
Describe what is meant by a direct current?
Current flows only in one direction only.
What does a fuse do in a plug?
Protects the user, melts if too high a current flows through it, breaking the circuit.
What colour is the live wire?
Brown
What colour is the neutral wire?
Blue
5 safety features of a 3 pin plug?
Fuse, Earth wire, Cable grip, colour coded wires, hard plastic coating.
What devices in the UK require an earth wire?
Devices with a metal casing.
What colour is the earth wire
Green and yellow (stripes)
How does the earth wire protect the user?
Earth wire is connected to the casing. If fault develops making the casing live, the earth wire provides a route back to socket.
If a current does flow down the earth wire what else happens to protect the user/device?
Earth wire has low resistance so large current flows and fuse melts to break circuit.
What type of metal are the pins on a plug made out of and why?
Brass - good conductor and is a strong metal. Also doesn’t rust or oxidise.
Some wires with in the house are thicker than others, why are thicker wires required sometimes? (wall sockets wires are thicker than the lighting wires)
Some devices require a higher current, thicker wires have less resistance and so thicker wires reduce the amount the wires heat up.
What happens when an electric current passes through a resistor?
The energy supplied to the resistor causes it to heat.
What is the national grid?
A system of cables and transformers, which transfer electrical energy around the country.
Why is it important for mains electricity to be A.C. when wanting to transport it through the national grid?
Transformers only work with AC supplies.
What does a step down transformer do?
Reduces the potential difference of the supply(for safety) which increases the current.
What is a step up transformer used for in the national grid?
Increases the potential difference which decreases the current ( lower current less energy wasted).
What appliances would only have a two core cable attached to them?
Appliances with a plastic casing.
How does a circuit breaker differ from a fuse?
Both switch off the circuit if too much current flows, but a circuit breaker can be reset.
Which wire is brown ?
The live wire
When would you only expect the earth wire to carry a current in it?
If a fault caused the live wire to become connected to the metal casing in a device.
What is current measured in?
Amps (A)
What is potential difference measured in?
Volts (V)
What is charge measured in?
Coulombs (C)
What is power measured in?
Watts (W)
What is energy measured in?
Joules (J)
What is the equation linking energy, power and time?
Power (W) = Energy(J) /time (s)
What is the equation linking power, current and PD?
Power = Voltage x Current
What is the equation linking Voltage (PD), energy and charge?
Energy = Charge x Voltage
What is the equation linking power, current and resistance?
P = (Current)2 x Resistance
What is the symbol for a fuse?
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