Paper 1 - 2b Domestic Electricity Flashcards
State the typical voltage for mains electricity?
230 V
State the frequency of mains electricity
50 Hz
Define a.c.
Alternating current, the electrons vibrate backwards and forwards. Mains electricity use a.c.
Define d.c.
Direct current. Electrons only flow in one direction. This is what we get from batteries
State the names and colours of the 3 wires found inside a cable.
Live wire - Brown Neutral wire - Blue Earth wire - Green and yellow stripes
Which pin is the earth wire connected to?
The top pin
Which pin is the live wire connected to?
The bottom right pin
Which pin is the neutral wire connected to?
The bottom left pin
Where is the fuse in a plug?
Between the live pin and the live wire
What is the role of the fuse?
If current gets too high the fuse melts and breaks the circuit, cutting off the live wire
How does the earth wire work with the fuse?
The earth wire is connected to a metal case. When there is an electrical fault, the live wire may also touch the metal case. This creates a parellel circuit. The earth wire has a low resistance. This increases the current drawn from the power supply, which melts the fuse on the live wire. This breaks the circuit and stops the metal device becoming live.
Why is the wire made of copper?
As copper conducts electricity and is ductile.
Why are pins made of brass?
As brass conducts electricity, do not rust and are hard to change shape.
Why is the plug made of stiff plastic?
As it is an insulator and it’s hard to change shape
What does the cable grip do?
It prevents the wires from snapping if tension is applied to the cable
Why do some electrical devices not have an earth wire?
As they are double insulated
Which wire can be missing from some appliances? Why?
Earth wire, if the appliance is plastic and you cannot get an electric shock from it.
State the role of the live wire
To carry the alternating potential difference from the supply to the component. the potential difference between the live and the earth is 230 V
State the role of the neutral wire
The neutral wire complete the circuit from the component back to the supply. The neutral wire is at or close to 0 V.
State the role of the earth wire.
It is a safety wire to stop an appliance becoming live. the earth wire is at 0V as it only carries a current if there is a fault.
State the relationship between power, potential difference and current.
Power = potential difference x current (P = VI)
State the units of power
Watts (W)
State the units of potential difference
Volts (V)
State the units of current
Amperes (A)
State the relationship between power, resistance and current.
Power = (Current)squared x resistance
State the units for resistance
Ohms
When using an electrical device what factors affect how much electrical energy it uses?
- Time it is used for 2. The power of the appliance
State the equation between energy transferred, power and time
Energy transferred (J) = Power (W) x time (s)
State the equation between energy transferred, charge and potential difference
Energy transferred (J) = Charge (C) x potential difference (V) E = QV
State the parts that make up the national grid
Cables, step up transformers, step down transformers
What does a step up transformer do? Why?
Increases the potential difference, which decreases the current. This reduces the amount of energy lost to heat so makes them more efficient.
What does a step down transformer do? Why?
Decreases the potential difference which increases the current. This makes them safer to use in homes.
