P5: Electricity in the home Flashcards
What are the two types of current
Alternating current
Direct current
What is direct current
Current flowing in one direction
What is alternating current
Current flowing in different directions
How much is our mains supply in the UK
230V with a frequency of 50 cycles per second (50HZ)
What is the period of an AC source
Time taken for a complete oscillation
What is the frequency of an AC source
Number of oscillations per second
How do we calculate the frequency of an AC source via an oscilloscope
1/period
What are the three core cables of the plug
Earth Wire
Live Wire
Neutral Wire
What is the live wire
A brown core cable, that carries a 230V potential. It provides the alternating potential difference from the mains electricity supply
What is the earth wire
A green and yellow striped core cable that has a 0V potential. It only carries the current if there is a fault. It is a safety wire to stop the electrical appliance from becoming live.
What is the neutral wire
A blue core cable that is is close to 0V which is the earth wire’s potential. It completes the circuit and carries current away from the appliance
How can we find out the power rating of an appliance
Check the label of the appliance
What is the equation that we can use to find the power rating of the appliance
Potential Difference X Current
What is the equation that links power, resistance and current
Power = Current X Current X Resistance
Or
Current squared X Resistance
How can we calculate the work done per second
We can calculate the energy an appliance transfers with the power rating and equation
Power X Time
Charge flow X Potential Difference
What is charge flow and what is it measured in
Charge flow is the amount of charge flowed through a circuit at a given point of time. It is measured in coulombs
What is the National Grid
A network of cables and transformers that connect power stations with houses and shops in UK.
Power stations carry an electric current which is an energy carrier
Why is a large power station better than a small one
They burn lots more fuel at high temperatures. It creates hot steam that turns turbines
Steam turbines are more efficient at higher temperatures.
Power stations produce electricity at 25000V
What is a step up transformer
They increase potential difference and decrease current. Therefore, this transfers less/low energy to the surroundings.
What is a step down transformer
They decrease the potential difference and increase the current. This is then delivered to the consumers to use
How do fuses and circuit breakers help us
They stop electric current flow if too high. It stops appliance from overheating
What is a fuse
They contain a thin wire that melts if the current flowing through an appliance is too high. This breaks the circuit and stops electric flow.
What is a circuit breaker
They are special devices that switch off current flow if current is higher than a certain value. We can use them lots of times despite providing the same jobs as fuses. But we must choose them both correctly to allow correct function
What are fuse ratings
Tells us the level of the fuse’s melting point. It has a value just above the normal current that an electrical appliance was.
For example if an operating current is 3.9A and fuses with values 3A, 5A and 13A are available, 5A is the best option
What are the three types of fuses
3A
5A
15A
What is an earthing metal case
They prevent electric shocks. If the case is touched by a wire inside the appliance, the current will flow through the earth wire. As they have a low resistance, a very high current will flow through, breaking the fuse in the device. This prevents current flow and secures the appliance
What are the dangers and risk factors of the live wire
They carry so much electrical energy making it dangerous. Even if the power is off, it is dangerous.
Live wires can still be risky when the mains switch is open (plug socket or light is turned off)
As it holds some potential difference
If a live wire is touched, our body supplies a link between the supply and the ground. In short, you get an electric shock.
An electric shock from the mains electricity supply is fatal (can kill you)
If we combine the live wire and the earth wire, the safety feature of the earth wire is removed. This takes a large quantity of current which would overpower our fuse
The fuse will then melt and explode
What are sources of direct current?
Batteries
Cells
