P2.5 Flashcards
Why do we use alternating current when switching a light on?
Because mains electricity is an ac supply.
What does an alternating current do?
Repeatedly reverses its direction.
What is a direct current? And why is it called this?
The current in the circuit.
Because it is in one direction only.
What two types of wire does every main circuit have?
- live wire
- neutral wire
Why does the current through a mains appliance alternate?
Because the mains supply provides an alternating potential difference between the two wires.
What is the potential difference between the live wire and earth referred to?
Voltage of the live wire.
Why is the live wire dangerous?
Because its voltage repeatedly changes from + to - and back every cycle.
What do we use a oscilloscope for?
To measure the peak potential difference and the frequency of a low voltage ac supply.
What does the Y-gain control tell us?
That each centimetre of height is due to a potential difference.
What happens when you plug in a heater with a metal case into a wall socket?
You Earth the metal case automatically.
Why are the outer casings of plugs etc of all mains circuits and appliances made of hard-wearing electrical insulators?
Because plugs etc contain live wires.
What are sockets made of?
Stiff plastic materials with the wires inside.
What do mains cables consist of?
Two or three insulated copper wires surrounded by an outer layer of flexible plastic material.
What is the colour of a live wire, neutral wire and Earth wire?
Live-brown
Neutral-blue
Earth-green and yellow
What do we use a fuse for?
For a mains appliance.
Why is a fuse always on the live side of an appliance?
Because if the fuse blows the appliance is then cut off from the live wire.
What is a circuit breaker?
An electromagnet switch that opens when there is a fault.
What do people use instead of fuses? Why?
Circuit breakers because they work faster and can be reset more quickly.
What is the RCCB?
Residual Current Circuit Breaker.
What does the RCCB do?
Cuts off the current in the live wire when it’s different from the current in the neutral wire.
What happens when the live wire inside an appliance touches a neutral wire? What is this called?
A very large current passes between the two wires at the point of contact.
Called a short circuit.
What happens when the fuse blows?
It cuts the current off.
What is the power of the appliance?
Energy it transfers.
What is the equation for power?
=energy transferred/time
