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Mains Electricity (Rough Notes) (Equations (Power = Current x Voltage …
Mains Electricity (Rough Notes)
Equations
Power
= Current x Voltage (P = I x V)
Voltage
= Current x Resitance (V = I x R)
Energy transfered
= Current x Voltage x Time
Energy
= Power x Time (E = p x t)
Freqeuncy
= 1/Time
1 Unit = 1KW h
1KW = 3.6 MJ
DC
- Direct Current
Movement of charge is in 1 direction
DC Voltage Source
- a voltage source that produces direct current
Example - Batteries, DC power supply
Waveform
(see source 1)
In most circuits current & voltage remains constant as time passes
On a current/voltage versus time graph is a straight line
AC
- Alternating Current
Current whose direction periodically changes
AC voltage Source
- a voltage source that produces alternating current
Example - Electrical outlets (in walls of home)
Waveform
(see source 2)
On a current/voltage versus time graph is Sine Curve
The Plug
(see source 3)
Live Wire
Has alternating voltage relative to neutral wire
Potentially most dangerous wire
Brown wire in UK
Neutral Wire
Completes the circuit
Voltage stay as about 0V
Blue wire in UK
Earth Wire
Not always there
Safety feature
Green & Yellow in uk
Cable
composed of 2 or 3 inner wires made of copper & encased in a plastic sleeve as it's an electrical insulator (reducing risk of eletrical shocks)
Safety
Earthing
(see source 6)
Creates a safe route for current to flow if live wire touches casing
Prevents Electricution
End of earth wire connects to ground
Earth wire has V.low resistance so a strong current flows & breaks the fuse
Double Insulation
Appliances that have a plastic casing don't need an earth wire
Plastic casing acts as insulator
Prevents an electric shock
Fuse
(see source 5)
Protects components
Connects to live wire & breaks the circuit if a fault in an appliance causes too mch current to flow in the live wire
How? When current is too great fuse wire heats until it melts & breaks the circuit
Fuse that is used should be smallest value above the normal current
Circuit Breakers
(see source 4)
Spring loaded push switch in closed position by spring loaded iron bolt. Electromagnet arranged so that it can pull bolt away
Responds quicker than a Fuse
When current in live is differnt to that of neutral wire electromagnet pulls bolt towards itself which releases switch into open position
Often called residual (leftover) current circuit breakers
Insulation
Wires covered in plastic
plastic is an insulator
Reduces risk of electrical shock
Hazards
Exposed/ Frayed wire
Could cause device to fail
Cause a fire
Cause an electric shock
Water
Water in humid air can conduct electricity
Shouldn't put in humid environments
Water decreases resitance of a persons body so a larger current can flow throgh the body
Electrical Power
All electrical appliances rely on the transfer of electrical energy into other forms
Current (in Amps) tells us how many Coulombs per second pass throgh appliance
Potential Difference (in Volts) tells us how many joules per coulomb of charge are transfered
Power = Current x Voltage