P5 - Electricity in the home...

P5 - Electricity in the home...

• Alternating current can change direction 
• Direct current flows in one direction only. 
• The Voltage of mains electricity is 50 Hz and frequency is 230v in Europe.

• The Live wire - carries the current that alternates between negative and positive and it's brown.

• Nuetral wire - completes the circuit, kept at 0v and its's blue. 

• Earth wire -  Saftey wire that earths appliences with a metal case. It's then safer to touch if there's a fault as it makes the current flow to earth and also blows the fuse. It's green.

• We use Alternating current as - you can change the voltage meaning you have a lower current, reducing heat.

• The National Grid:
• Increase Voltage, Reduce current = reduce in waste
• Efficient system 
• Step up transformer = more voltage 
• Step down transformer = less voltage

Equation time!!! 

frequency of ac supply = 1 / time for one cycle

Half wave refraction: 

Making the current flow in one direction from ac to dc. we use diodes for this.

Goes from being a full wave to only a half one as shown in diagram. 

• Made of copper - good conducter and it's sustainable. 
• Each wire is cased in plastic - stops short cuirciting, plastic is good insulator.

A way of remembering the wires: 

Neutral wire is BLue and in the Bottom Left. 

Live wire is BRown and in the Bottom Reft

• Power (W) = energy (J) / time (S)

• Power = Current (A) x Voltage (V)

• Power = Current ^2 (A^2) x Resistance (ohms)

( 1 watt = 1 joule per second

• Charge = Current x time 

• When charge flows through a resistor, energy is transferred to the resistor and it gets hotter. 

• Energy (E) = Charge flow (Q) x Potentiall Difference (V) 

• Energy (E) = Power (P) x time (t) 

• Energy (E) = Potentiall difference (V) x Current (I) x time (t)

• An electricity meter measures how much energy is supplied to a house. 

• Energy transferred (to applience) (J) = power (W) x time (s) 
• units used (Kwh) = Power (Kw) x time (H)

• Efficinecy (%) = Useful energy out / Total energy in x 100 
• OR 
• Efficiency (%) = Useful power out / total power in x 100