P5 electricity in the home Flashcards
What is a direct and alternating current?
A direct current flows in one direction only e.g. a torch and an alternating current repeatedly reverses its direction of flow e.g. a switch in a house
What wires does a mains circuit have?
A live wire is alternately posistive and negative every cycle at 325V and a neutral wire at zero volts. This is because the mains supply provides an alternating potential difference between the two wires.
How to measure frequency?
1/time taken for 1 cycle
How to find the peak potential difference of an alternating current?
You need to get the maximum voltage measured from zero volts
What are step up and step down transformers?
Step down transformers are used to supply electricity from the national grid to consumers. Homes and offices are supplied with the same power as a 230V direct current-supply.
Step up transformers are used at power stations to transfer electricity to the national grid.
What materials are plugs made of?
The outer part is made of plastic usually as it does not conduct, the pins are made of brass as it is a good conductor and doesn’t rust or oxidise. It also contains a fuse between the live pin and the live wire so if too much current flows through it will melt and cut the circuit off.
What colour are the wires?
The live wire is brown the neutral wire is blue and the earth wire is green and yellow striped.
How to calculate power?
Power, P(watts, w) = energy transferred, E (joules, J) / time, t( seconds, s)
How to find power supplied?
Powe supplied, P(watts, w) = current, I(amperes, A) x potential difference, V(volts, V)
How to find the right fuse?
electrical power(watts) / potential difference(volts)
How to calculate charge?
charge flow, Q(coulumbs, C) = current, I(amperes, A) x time, t(seconds, s)
How to find the energy transferred to a resistor in a given time?
energy,E=charge flow, Q x potential difference, V
How to find energy transferred from the mains?
energy transferred from the mains, E(joules, J) = power, P(watts, W) x time, t (seconds, s )
How to find efficiency?
efficiency=(output power/input power) x100
What does the earth wire do?
It is connected to the ground and is at 0 volts and carries a current only if there is a fault. It is connected to the longest pin in a plug and is used to earth the metal case of a mains appliance.
What does a domestic energy meter do?
It measures how much energy is supplied.
What voltage do step up transformers make it?
400,000 V
What voltage do step down transformers make it?
230 V
Why are step up transformers used?
To deplete the current due to the heat generated because of high levels of resistance.
Why are step down transformers used?
To reduce the voltage as it would blow appliances in our house.
When does an alternating current occur?
When we use an alternating potential difference, going from +240 V to -240 V and therefore a + and - current.
What Hz is the UK system?
50 HZ
When does a direct current occur?
When the voltage is continuously positive or negative and charge is always flowing in the same direction.
What device is used for a P.D time graph?
An oscillope
