Chapter 5 🗽 Flashcards
What is the equation for energy transferred from the mains?
Energy transferred from the mains (J)= power x time
What is the equation for power supplied (W)?
Power = current x potential difference
How do electrical appliances waste energy?
Heating the surroundings
Friction in moving parts
Equation for efficiency
Efficiency = output power/input power x 100
What is charge flow?
The electrons being forced round a circuit
Equation for charge flow
Charge flow (C) = current x time
When the charge flows around a circuit for a given time, the envy supplied by the battery is equal to what?
The energy transferred to all the components in a circuit
Why does a resistor get hot when charge flows through it?
Energy is transferred to the resistor because the electrons collide with the resistor ions, heating it up
What is the equation for power?
Power = energy transferred/time
What is the current in an electrical appliance?
The current is the charge that flows through it each second
What is the potential difference of an electrical appliance?
The energy that is transferred to the appliance by the charge passing through it
Equation for power supplied?
Power supplied = current x potential difference
Equation for power using current and resistance
Power = current^2 x resistance
What does the earth wire do?
It carries the current into the earth if something goes wrong
Why are plugs, sockets and cables made of insulators?
To stop them carrying a current
What is the potential difference of the earth wire?
0V
Why are the pins made of brass?
Brass is a good conductor and doesn’t rust
What does the fuse do?
If the current gets too high, it melts and cuts the live wire off
Which is the brown wire?
The live wire
Which is the blue wire?
The neutral wire
Which is the yellow and green wire?
Earth wire
Why is plastic used?
It is a good insulator so you don’t get an electric shock
What are two core cables used for?
Appliances with plastic cases
Why must some wires be thicker than others?
Carry different currents
What happens when a plug short circuits?
The live wire touches the neutral wire
Why is copper used in the wires?
It is a good conductor and bends easily
What is a direct current?
When the current flows in only one direction
What is an alternating current?
When the current repeatedly reverses direction
What is frequency in the uk mains?
50Hz
What is a step up transformer?
Used to make the size of the potential difference much bigger
What is a step down transformer?
Used to supply homes with electricity from the national grid
Takes voltage down to manageable level
How do you measure the frequency of an ac supply?
Frequency = 1/ time taken for one cycle
what does the live wire do?
carries current to the appliance
what does the neutral wire do?
carries current away from the appliance
1 kw
1000 w
What are the two ways in which efficiency can be expressed
Ratio or percentage
Why do electric appliances ways energy because of the wires
The wires have some resistance so the energy is transferred as heat
What does a domestic electricity meter measure
How much energy is supplied with
What is the energy supplied by the battery equal to
The energy transferred to all components in the circuit
How to determine what fuse to use
Use the equation current = power / PD
You use the fuse closest to it
What determines whether an appliance should have a 3 or 2 core cable
2 core cables are for appliances with plastic cases
Why are some wires thicker than others
Carry more charge
What causes a short circuit
When the live wire touches the neutral wire
Difference between 2 and 3 core wire
2 core doesn’t have an earth wire
What is the PD of electricity in the UK
325 v
Why is the PD of the national grid so high?
Much less current is needed to transfer same amount of power
What is the live wire in a mains circuit charge like
Alternately positive and negative
Which wire is earthed at the local power station?
Neutral
What does double insulated mean?
The wires are coated in plastic and the outer case of the appliance is plastic
