P5 - Electricity In The Home✔️ Flashcards
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
State the units for the equation linking power, resistance and current?
- Power, P = W
- Current^2 = A
- Resistance = Ω
State the equation that links charge flow, current and time?
Charge flow = current x time
State the units for the equation that links charge flow , current and time?
- Charge flow - coulombs, C
- Current - amperes, A
- Time - seconds, s
Why does a resistor heat up - mention electrons and energy stores?
When a resistor is connected to a battery - work is done by the batter to make electrons pass through the resistor - each electron repeatedly collides with the vibrating metal ions of the resistor transferring energy to the ions - so the ions of resistor gains kinetic energy and vibrate even more - causes the resistor to become hottor
State the equation for energy transferred when given power?
Energy transferred = power x time
State the units for the equation linking energy transferred, time and power?
- Energy transferred, E - joules (J)
- power, P - watts (W)
- time, t - seconds (s)
State the equation that links power, current and potential difference?
Power, P = current x potential difference
State the units for the equation linking power, current and potential difference?
- power,P - watts (W)
- Current,I - amperes (A)
- Potential difference,V - volts (V)
Equation for efficiency?
Efficiency = (output power/input power) x 100
Why are elctrical appliances never 100% efficient?
There is always waste energy because the current in both the wire and components of the appliance has a heating effect due to the resistance of the wires and the components - energy is transferred to the surroundings - which causes the temperature to increase
Why are elctrical appliances with moving parts never 100% efficient?
Electrical devices with moving parts like motors waste energy due to the firction between the moving parts which heats them up and transfers energy to the surrounings
Explain how transformers increase the pd?
Step-up transfomer - has more turns on the secondary coil than the primary coil as the pd is increased the current is decreased
