P2.4 - Mains Electricity Flashcards
What is alternating current?
Current that repeatedly reverses its direction.
What is direct current?
Current in one direction.
What is the peak voltage of an alternating pd?
The maximum voltage measured from zero.
How is the frequency of an alternating current calculated with an ocilloscope?
Freq. = 1 / time taken for one cycle
What is the casing of mains electricity devices made of and why?
Stiff, thermosetting plastic because it is a good insulator.
What is in a mains cable?
Three insulated copper wires surrounded by a plastic outer sleeve.
What colour is the live wire?
Brown
What colour is the neutral wire?
Blue
What colour is the earth wire?
Yellow and green
Why does a three pin plug have an earth pin?
So the metal case of a mains appliance is insulated.
What are plug pins made of?
Brass because it is a good conductor and doesn’t rust.
What is a fuse used for?
The appliance is cut off if the current is too high.
Why is a fuse in between the live wire and pin?
The appliance can be cut off from the current if the fuse blows?
What is a circuit breaker?
An electromagnetic switch that trips in the event of too much current passing through.
Why aren’t appliances with plastic cases earthed?
Plastic is an insulator so cannot become live.
How does a fuse work?
A fuse contains a thin wire that heats up and melts if too much current passes through.
What is the rating of a fuse?
The maximum current that can pass through without melting the wire.
Give three advantages of using an RCCB.
- It works faster than a circuit breaker
- It can be used where there is no earth
- It is more sensitive.
How does an RCCB work?
An RCCB trips when the current in the live wire is different to the current on the neutral wire.
What is the relationship between power and energy?
The power supplied to a device is the energy transferred each second.
What is the equation for power of an appliance?
Power (W) = energy transferred (J) / time (s)
What is an electrical current?
The rate of flow of charge.
How is the flow of electric charge calculated by the current?
Charge (Coulombs) = current (amps) x time (seconds)
What energy transfers take place when charge flows through a resistor?
The energy transferred makes the resistor hot.
