P5- Mains electricity Flashcards
When does electricity demand peak?
Late in the afternoon
The formula for electric power is?
Power= voltage x current
What are step up transformers?
Increases the voltage and decreases the current.
What are step down transformers?
Decreases the voltage and increases the current
How does electric power enter our homes?
- Electric power is generated at a power station
2.Step up transformers increase the voltage but decrease current. - The electric power is transmitted via the national grid at low current which minimizes power loss.
- Step down transformers decrease the voltage and increase the current.
- Electric power is wired into our homes at a voltage that is relatively safe to use.
What is the max value of mains voltage?
230V
What is a furnace?
Part of a power station where fossil fuels are burnt to heat water.
What is a Turbine
Part of a power station. The high pressure steam is forced through a turbine, making it turn.
What is a generator?
In a power station, the turbine is attached to a generator which turns to generate electricity at a voltage of around 25000v
What is the national grid network?
Electricity that is transported across the country by vast networks of cables and transformers.
What is direct current?
Current that flows in one direction.
What is alternating current?
A current that repeatedly reverses direction, it has a frequency of 50hz, which means its changing direction is 50 times per second.
What is alternating current caused by?
An alternating potential difference
What do alternating current and voltage graphs look like and why?
Wavy like a sound wave.
Because the value alternates between positive and negative.
Direct current is supplied by?
Cells and batteries
What is used for mains supply?
Alternating current.
The role of an oscilloscope is to?
Display how voltage changes with time.
What does a direct current graph look like?
A straight line
How many wires are usually in an electric plug?
3
What are the three wires that are normally present in UK plugs?
Neutral wire,
Earth wire,
Live wire
Wires are made of what and coated in a layer of insulating what?
Copper and coated in plastic.
What color is the Earth wire?
Green and yellow
What color is the live wire?
Brown.
What wire prevents the electrical casing from becoming live?
The earth wire
What color is the neutral wire?
Blue
What wire supplies the current to the appliance?
The live wire.
Which wire completes the circuit and allows the current to flow?
Neutral wire
What is the voltage of the neutral wire?
0 V
What is the voltage between the live and neutral wire?
230 v
Which two wires have the same voltage?
Earth and neutral wires.
What can happen if there is a sudden increase in current within an electric circuit?
It can damage the appliance, cause a fire or give an electric shock.
Safety features used to protect against surges in current.
Fuse and circuit breakers.
How do fuses work?
They have a thin wire that melts and breams the circuit when the current is too high.
They prevent FIRES.
The RATING of a fuse is the current that will cause the fuse to break the circuit.
Generally you should use a fuse with a rating a few amps above the recommended current for the appliance.
What is a circuit breaker?
A fuse that can be reset after they break the circuit.
How do earth wires protect us from electric shocks?
- The earth wire is connected to the casing of the appliance.
- If the live wire touches the appliance casing, the earth wire provides and alternative pathway for electricity to flow.
what does double insulation mean?
The appliance has plastic casing but no earth wire.
Power supplied to the appliance is the?
Energy transferred per second.
Potential difference across the appliance is the
Energy transferred by each bit if charge through it.
Current is the —————————— in an appliance
Charge per second.
Equation for power in electrical power
Power = energy/ time
1 watt=
1 joule per second.
