2b-Mains electricity Flashcards
Q: How does earthing help prevent electric shocks?
A: If the live wire touches the metal casing of an appliance, the current is directed to the ground instead of passing through a person.
Q: What is insulation, and how does it protect users?
A: Insulation is the use of non-conductive materials (like plastic or rubber) to cover live wires. This prevents users from touching the live wire and getting an electric shock.
Q: What is double insulation, and how does it provide protection?
A: Double insulation means an appliance has:
Insulated wiring (internal protection).
A non-conductive outer casing (usually plastic) to prevent any risk of electric shock.
Example: Hairdryers and phone chargers.
Appliances with double insulation do not require an earth wire.
Q: What is earthing, and why is it important in electrical appliances?
A: Earthing provides a low-resistance path for electricity to flow to the ground in case of a fault.
If the live wire touches the metal casing, the current flows through the earth wire instead of shocking the user.
This prevents electric shocks and reduces fire risks.
Example: Cookers, washing machines, and fridges (metal-cased appliances).
Q: What is the role of a fuse in an electrical circuit?
A: A fuse is a thin wire that melts when excessive current flows through it.
How it works:
If the current is too high, the fuse melts and breaks the circuit, stopping electricity flow.
Purpose: Protects appliances and users from overheating, fires, and electric shocks.
Example: TV sets and kettles use fuses rated slightly above their operating current.
Q: How does a circuit breaker work, and why is it better than a fuse?
A: A circuit breaker is an automatic safety device that switches off the circuit when it detects a surge of current.
Advantages over fuses:
Can be reset (instead of being replaced like a fuse).
Faster response time to electrical faults.
Example: Used in home fuse boxes to prevent electrical fires.
Q: Why does a current in a resistor result in heat generation?
A: When current flows through a resistor:
Electrons collide with atoms in the resistor.
This causes atoms to vibrate more, increasing thermal energy.
As a result, electrical energy is converted into heat.
Example: Electric heaters, kettles, toasters.
Q: How is the heating effect of current used in domestic appliances?
A:
Toasters: Heat is used to brown bread.
Kettles: Heat is used to boil water.
Electric ovens: Convert electrical energy into thermal energy to cook food.
Fuses: The heating effect melts the fuse wire, breaking the circuit if current is too high.
Q: What is the difference between alternating current (AC) and direct current (DC)?
A:
Alternating Current (AC):
The current direction changes periodically.
Used in mains electricity (230V, 50Hz in the UK).
Example: Power from wall sockets.
Direct Current (DC):
The current flows in one direction only.
Supplied by cells and batteries.
Example: Phones, laptops, torches.
Q: Why is mains electricity AC and not DC?
A:
AC can be transmitted over long distances efficiently using transformers.
AC voltage can be easily stepped up or down to reduce energy loss.
DC is mainly used for portable devices like phones and laptops.
