Mains Electricity Flashcards
What is Direct Current (DC)?
Current flows in one direction only, maintaining a constant voltage (e.g., batteries, solar cells).
What is Alternating Current (AC)?
Current changes direction periodically, meaning voltage fluctuates from positive to negative.
What is the mains electricity voltage and frequency in the UK?
Mains electricity in the UK is 230V AC at 50Hz, meaning the current changes direction 50 times per second.
Why is AC used for mains electricity?
AC can be easily transformed to different voltages for transmission.
What is insulation in electrical wiring?
Wires are coated with non-conductive material (e.g., rubber, plastic) to prevent electric shocks and short circuits.
What is double insulation?
Appliances with a plastic casing do not need an earth wire since there is no risk of the casing becoming live.
What is the purpose of earthing?
If a fault occurs and the live wire touches the metal casing, the earth wire provides a low-resistance path to the ground, directing the excess current away and preventing electric shocks.
What is the function of a fuse?
A safety device designed to protect appliances from excessive current.
The fuse contains a thin wire that melts if current is too high, breaking the circuit.
Prevents overheating and fires.
What are circuit breakers?
As electrons flow through a resistor, they collide with metal ions, causing the ions to vibrate more.
This increases the internal energy (thermal energy) of the resistor, making it hotter.
This is useful in appliances like electric heaters, toasters, ovens, and kettles, where heat generation is needed.
Higher current or resistance leads to more collisions, increasing the temperature further.
What is the purpose of a fuse in an electrical circuit?
A safety device designed to protect appliances from excessive current.
The fuse contains a thin wire that melts if current is too high, breaking the circuit. Prevents overheating and fires.
Why does a current in a resistor cause energy transfer?
As electrons flow through a resistor, they collide with metal ions, causing the ions to vibrate more, increasing the internal energy (thermal energy) of the resistor.
What is the equation for electrical power?
Power is the rate at which energy is transferred in a circuit.
Where: Power (Watts, W), Current (Amperes, A), Voltage (Volts, V). Higher power appliances draw more current.
How should a fuse be selected based on current?
A fuse rating must be slightly higher than the normal operating current to prevent unnecessary breaking.
Example: If an appliance operates at 5A, a 3A fuse would blow immediately, so a 5A or 7A fuse should be used.
What is the equation for electrical energy transfer?
Electrical energy transferred depends on current, voltage, and time.
Where: Energy transferred (Joules, J), Current (Amperes, A), Voltage (Volts, V), Time (seconds, s).
How is energy usage measured for billing?
Energy companies measure usage in kilowatt-hours (kWh) for billing purposes.
What are the three wires in a plug?
Live wire (brown): Carries high voltage (230V in the UK). Neutral wire (blue): Completes the circuit. Earth wire (green and yellow): A safety wire that prevents electric shocks.
Why are wires in a plug covered with insulation?
To prevent electric shocks by stopping direct contact with live wires.
To avoid short circuits by keeping wires from touching each other.
Insulation is made of rubber or plastic, which are good electrical insulators.
How can electrical appliances be made safer?
Fuses prevent excessive current by breaking the circuit if the current is too high.
Double insulation removes the need for an earth wire by preventing any live parts from touching the outer casing.
Circuit breakers detect faults and immediately cut off power, unlike fuses that need replacing after breaking.
