P5 - Electricity in the home Flashcards
What direction does d.c travel in?
D.c. flows in one direction only.
What direction does a.c. travel in?
A.c. repeatedly reverses its direction of flow.
What is the UK mains frequency?
50 cycles a second.
What is the brown wire connected to?
The live pin.
What is wire is the live pin connected to?
Brown wire.
What is the blue wire connected to?
The neutral pin.
What are the two equations for power (with units)?
Power (w) = energy transferred (J) * time (s)
Power (w) = current (a) x p.d. (volts)
How do you work out the period?
Period is the time taken for one complete oscillation (seconds).
What is the equation of frequency?
Frequency(Hz) = 1 * period (s)
How do you work out the efficiency of an appliance?
Efficiency = Total useful output * Total input
How do you work out charge flow?
Charge flow (c) = current (a) x time (s)
What is the equation of energy transferred?
Energy transferred = charge (c) x p.d. (v)
E
—————————–
Ch x p.d.
Calculate a current across a lamp when the power of the lamp is 0.15W and the p.d. is 1.5V?
Current = 0.15W * 1.5v = 0.1A
If a current is 8.3A, what fuse is required?
13A
If a current is 2.2, what fuse is required?
3A
Explain the role of a step-up transformer.
Increases the voltage and decreases the current which reduces the energy lost.
Explain the role of a step-down transformer.
Decreases the voltage and increases the current.
Give the definition of the national grid.
A system of transformers and high voltage cables which connect power stations to consumers (home) to provide electricity.
Why is it important that the voltage and current are changed at the step up and step down transformers?
So that high voltage transmission lines get the correct voltage and consumers are safe.
Give two advantages if burying cables underground?
- Not affected by bad weather
- More reliable
- Hidden from sight
- Minimal maintenance needed.
Give two disadvantages of burying cables underground?
- Hard to set up
- Lots of disturbance to land
- High set up costs
- Hard to access faults
What are the four main stages that happen for power stages to generate electricity?
- The fuel is burned to boil water to make steam.
- The steam makes a turbine spin.
- The spinning turbine turns on a generator which produces electricity.
- The electricity goes to the transformers to produce the correct voltage.
What is the difference between a coal power station and a nuclear power station?
Coal power stations use fuel whereas nuclear power stations use fuel roads containing radioactive waste.
Why is a plug made out of plastic?
It is a good electrical insulator and prevents eclectic shocks.
Why are the pins of a plug made out of brass?
It is a good conductor of electricity and it is hard.
How do you work out the charge of an appliance?
Energy transferred * p.d.
What is current measured in?
Amps (A).
Charge (C) x potential difference (V) is the equation for finding out what?
Energy transferred.
Total useful output * total input is the equation for finding out what?
Efficiency.
What is the role of a fuse?
The fuse helps protect the wiring.
If a large current goes through the live wire, the fuse melts and breaks the circuit which switches off the appliance.
What is the equation for power (energy transferred)?
Power (W)= energy transferred * time (S)
What is the equation for power (current)?
Power (W) = current (A) x p.d. (V)
