2.b Mains Electricity

Electric Current

.- A flow of electrons .-Needs a COMPLETE CIRCUIT

2.3 Uses of Circuit Breakers

.- same as the fuse but in a different way: .-If there is an increase in current the circuit breaker SPRINGS OPEN a switch → open circuit .-Reset easily after fault fixed

Mains electricity cable

.-2 or 3 inner wires .-Inner core copper .- outer layers: flexible plastic .- inner wires are colour coded: blue →neutral brown→live green and yellow stripes→earth

2.3 Uses of double insulation

.-Appliances made with PLASTIC casing do not need EARTH wire as the plastic is an INSULATOR .-called DOUBLE INSULATED

Coulomb

.-C .-CHARGE of 1 A

Amperes

.-Electric current is MEASURED in Amperes .-Amps. A .-1 ampere = 6 x 10¹⁸ electrons per second

Potential Difference

.-Electrons passing through a lamp lose some of the electrical potential energy to the thin wires in the lamp in the form of heat and light → across the lamp there is an electrical energy difference .- This difference is a "POTENTIAL DIFFERENCE or p.d. or Voltage -.Measured in "Volts" ,V

2.3 Uses of Fuses

.-Fuse fits between live wire (brown wire) and the PIN. .- BREAKS THE CIRCUIT IF TOO MUCH CURRENT FLOWS .-Contains a piece of wire that melts easily If current too great .-Standard ratings:3A, 5A and 13A. Fuse should be slightly higher current than the device needs: e.g. if the device works at 3A, use a 5A fuse

2.3 Uses of insulation

.-Insulation means putting a material that does not conduct electricity around a live conductor. .-insulator: material that does not conduct electricity .-Any non-metal is a good insulator( exception of graphite). Usually plastic is used.

2.3 Uses of Earthing

.-Many electrical appliances have metal cases e.g. washing machines. .-earth wire creates a SAFE ROUTE for the current to flow through if the LIVE WIRE TOUCHES CASING

Ammeter circuit

.-Measure the electricity current, Amperes

Switch

.-ON : switch completes the circuit → current flow .-OFF: gap in the circuit → current can't flow

Battery

.-PUSHES the ELECTRONS around the circuit. .-How?transferring CHEMICAL ENERGY from the battery to POTENTIAL ENERGY in the ELECTRONS

Resistance

.-Property of an object of resisting or opposing the flow of electrical current. .-measured in "Ohms", Ω

Electric current passing through components, e.g.lamp

.-The electric current IS NOT USED → A is the same before and after pass the bulb .-Electrons passing through a lamp GIVE UP some of the ELECTRICAL POTENTIAL energy to the thin wires in the lamp in the form of HEAT and LIGHT → electrical energy difference

UK mains electricity

.-about 230V in UK .-houses with main electricity have a DISTRIBUTION BOX that takes all the house electricity and send it to different rooms

3 pin plug

.-case from tough plastic or rubber →good electrical insulators. .-3 pins made from brass →good conductor of electricity. .-Fuse between the live terminal and the live pin. .-blue and brown cable carry the CURRENT .-Where connect each cable? 2nd letter: bLue → left bRown →right sTriped →top

ELECTRICAL ENERGY DIFFERENCE

.-electrons give energy when passing through lamp creating an electrical energy difference

Metallic wire

Contains large number of free electrons that move easily from atom to atom

Why current goes through the earth wire instead of casing?

Earth wire has very low resistance

2.6 Energy transferred formula

Energy transferred = current x time E = l x V x t

2.2 Hazards of electricity

Hazard → Danger 1.Frayed Cables → wiring can become exposed 2.long trailing cables → these might cause a fall 3.damage plugs → wiring can become exposed 4.water around sockets → water conducts, so can connect a person into the main supply 5.-pushing metal objects into sockets → this connects the holdr to the main supply and is likely to be lethal

Most important aids to the safe use of electricity

INSULATION and FUSES or CIRCUIT BREAKERS

Voltmeter

Potential difference is measured by a Voltmeter.

2.5 Power formula

Power = Current x Voltage P = l x v

2.4 Current in a Resistor

Results in the electrical transfer of energy and an increase in temperature and how this can be used in a variety of domestic context

What hapens if the live wire inside the appliance touches metal casing?

You will get an electric shock

copper and plastic

copper: good conductor of electricity plastic: good electrical insulator