13. Safety and National Grid Flashcards
1
Q
what are the differences between batteries and mains?
A
- cells have chemical stores which are transferred electrically, mains depends
- constant low voltage, alternating high voltage
- DC, AC
- 50Hz is typical freq for UK mains
2
Q
why is the wire in the cable made from copper?
A
conductor, flexible
3
Q
why is the wire casing made from flexible plastic?
A
insulator, flexibel
4
Q
why are the plug pins made from brass?
A
conductor, rigid
5
Q
why is the plug casing made from stiff plastic?
A
insulator, rigid
6
Q
what colour is the live wire and what does it do (plug)
A
- brown
- high voltage
- carries current that alternates between neg and pos volatge
7
Q
what colour is the earth wire and what does it do?
A
- green
- safety wire used to earth appliances w a metal case
8
Q
what colour is the neutral wire?
A
- completes circuit
- kept at 0 voltage
9
Q
how do fuses work?
why are they needed and explain fuse ratings
A
- surge in current could damage an electrical appliance
- fuse contains thin wire -> melts if current too hgh
- this breaks cirucit and elecrticity unable to flow
- fuse rating gives current for which the fuse will melt eg 3A fuse
- should be slightly larger than normal operating current
10
Q
what is earthing?
A
- reduces chance of shock
- earth wire connected to casing of metal device to provide alternative path for current if fault occues
- if live wire becomes loose and touches metal case, v large current flows (low resistance) to eath and melts the fuse wire breaking circuit
11
Q
what are double insulated appliances?
A
- plastic casess
- case cannot become live, doesn’t conduct
- if one layer of insulation damaged the appliance is still safe
12
Q
what are circuit breakers?
A
- circuit broken by using an electromagnet to pull two wires apart
