2b mains electricity Flashcards
1
Q
What is dc?
A
- Direct current is current that flows in one direction only
- A cell or battery supplies direct current
2
Q
What is ac?
A
- An alternating current is one which is constantly changing direction
- Main electricity is an ac
3
Q
What are the 3 different wires?
A
Live wire: brown
Neutral wire: blue
Earth wire: yellow + green
4
Q
What is current?
A
- Current is the rate of flow of charge (amount of charge flowing per second)
- We measure current in Amps (A)
- We measure it using an ammeter
5
Q
What is an earth wire?
A
- Earth wires are needed if the case of an appliance is made of a conductor (eg metal)
- The Earth wire provides a connection between the metal case and the Earth
- If the live wire touches the case, the earth wire provides a low resistance path to Earth. This means the current increases, which causes the fuse to melt, breaking the circuit and stopping the flow of current
6
Q
What is the equation for energy transferred?
A
Energy transferred = Current x Voltage x Time
J = A x V x S
Power = Energy Transferred/ Time
7
Q
What is a circuit breaker?
A
Circuit Breakers (RCCBs) - Residual current circuit breakers
- If too much current flows through a circuit breaker the springs unclamp
- Circuit breakers can be reset and reused whereas a fuse must be replaced
- Circuit breakers stop the current more quickly than fuses
8
Q
What is double insulation?
A
- Double insulation is when a device has a case that is completely made of an insulator (eg plastic)
- Double insulated devices do not need an earth wire
9
Q
What is a fuse?
A
- Fuses are a safety feature
- If the current in a fuse gets too high, the fuse melts, breaking the circuit and stopping the current from flowing
- Rating - The value of current that will cause the fuse to melt
10
Q
What is a heater?
A
- Any component with resistance will transfer energy to a thermal store
- Electrical heater work using electrical resistance
11
Q
What is the equation for power?
A
Power = current x voltage
W = A x V
