Physics - Domestic electricity Flashcards
What is the equation for cost?
Cost = Units used x cost per unit
What is an A.C power supply?
Alternating current - When the current constantly changes direction. Used as Mains electricity.
What is a D.C power supply?
Direct current - When the current only flows in one direction. Used in batteries or solar cells.
What does a fuse do?
The fuse breaks the circuit if a fault in an appliance causes too much current to flow. This protects the wiring and the appliance if something goes wrong. The fuse contains a piece of wire that melts easily. If the current going through the fuse is too great, the wire heats up until it melts and breaks the circuit.
What does a circuit breaker do?
These are automatically operated electrical switches that protect electrical circuits from overloading or short circuiting. They detect faults and then stop the flow of electricity.
What is an MCB?
Miniature circuit breaker. It can be reset and uses an electromagnet to open a switch if the current goes above a certain value. MCBs switch off the current faster than a fuse.
What is an RCCB?
Residual current circuit breaker. It switches off the circuit when there is a difference between the currents in the live and neutral wires of the appliance. RCCBs are more sensitive than MCBs.
What is the difference between a MCB and a RCCB?
MCBs protect the circuit and RCCBs protect the user.
How is the wiring connected in the mains supply?
The wiring in a house connects all appliances together in parallel. This is so that each appliance has the mains supply of 230 volts across it, and also so that they can all be switched on and off independently.
What is a ring circuit?
In a ring circuit the live, neutral and earth wires form a loop of cable going from the consumer unit to all of the sockets in turn and then back to the consumer unit.
What is the consumer unit?
The consumer unit contains the main switch and the fuses for all of the fixed circuits, such as the power ring circuit and the lighting circuit.
What is the function of the live wire?
The live wire carries current to the house/appliance at a high voltage.
What is the function of the neutral wire?
The neutral wire completes the circuit and carries current away at low/zero voltage.
What is the function of the earth wire?
The earth can carry current safely into the ground if a fault develops in a metal framed appliance. This would also blow the fuse / trip the MCB.
What are the advantages of the ring main?
-The cables can be made thinner as there are two paths for the current.
-Each part of the cable carries less because the current flows both ways.
-A ring main is more convenient as sockets can be place anywhere on the ring.
-Each socket can be operated separately.
