P5 - Electricity In The Home✔️ Flashcards
(36 cards)
What is direct current (d.c.)?
Current which goes arround the circuit in only one direction, example: is batterys used to power a torch
What is alternating current (a.c.)?
Alternating current repeatedly reverses its direction - flows one way then the other way in successive cycles - used for powering a light in your home because the mains electricity is an a.c. Supply
What does a mains circuit involve?
A live wire which is alternately positive and negative every cycle, and a neutral wire at zero volts
What is the job of step-up transfomers?
Used at power stations to transfer electricity to the national grid - used to make the size of the alternating potential difference much bigger typically from 25,00 V to about 132,000V - decreases the current
What is the job of step-down transfomers?
Used to supply electricity from the national grid to consumers - decreases the volatge and increases the current
what is mains frequency?what is the value of the uks?
The number of cycles an alternating current passes through each second - uks main frequency is 50 cycles per second or 50Hz
Why is the national grids potential difference (voltage) made very high when transporting electric?
Means less current is needed to transfer the same amount of power - so the power loss due to the resistance heating in the cables is much reduced
Equation for working out the frequency of an a.c. Supply?
Frequency = 1 / time taken for 1 cycle
What is the national grid?
the network of cables and transformers that transport electricity from the power stations in Britain
Voltage of uk main electricity supply?
230V
What is the live wire? what colour is the wire?
Carries the alternating potential difference (voltage) from the supply - coloured brown
What is the neutral wire? What colour is it?
Neutral wire completes the circuit - earthed at the local electricity substation - at zero volts - the colour of the wire is blue
What is the earth wire? what colour is it?
Is a safety wire to stop the appliance becoming live which could electrocute you - the colour of the wire is green with yellow stripes - it is at zero volts and carries a current only if there is a fault
What materials are sockets and plugs made of? Why?
Made up of stiff plastic materials that enclose the electrical connections - plastic is used because it is a good electrical insulator
Describe the structure of a mains cable?
Made up of two or three insulated copper wires surrounded by an outer layer of flexible plastic material - copper is used because it is a good electrical conductor and bends easily
What is the earth wire connected to?why is it needed?
Connected to the longest pin in a plug and is used to earth the metal case of a mains appliance - which stops the metal case becoming live and electrocuting you
Why do plugs contain a fuse?
Plugs contain a fuse between the live pin and the live wire - if too much current passes through the wre in the fuse, it melts and uts the live wire off
What are the pins on a plug made of? Why?
Pinds are made of brass because it is a good conductor and doesn’t rust or oxidise and is harder the copper
State the equation for power, P?
Power, P = energy transferred, E / time, t
State the units for the equation linking power, energy transferred and time equation?
- Power, P = watts
- Energy transferred, E = joules
- Time, t = seconds
State the equation that links power supplied, P with current and potential difference?
Power supplied = current x potentital difference
What are the units for power supplied, current and potenital difference?
- Power supplied, P = watts (W)
- Current, i = amperes (A)
- Potential difference = volts (V)
Example of 3 fuses ratings?
- 3 A
- 5 A
- 13 A
State the equation that links power,P with current and resistance?
Power, P = (current ^2) x resistance
