Practical Electricity
Neutral wire
-Blue -completes circuit by forming path for current back to supply
Live wire
-Brown -Delivers current at high voltage from supply to applaience
Switches
-Fitted into live wire,so that switching off disconnects the high voltage from the appliance, if connected to neutral,aplliance could be live -Connect and disconnect the circuit -
Earth wire
-Green and yellow -low resistance, connected to metal casing
Heating in Electric Iron
-Heat is generated when current passes through the heating element -Heat is spread out thanks to the large surface area of the metal iron,which is a good conductor of heat -A thermostat inside the iron controls the temperature of the heating element.
Heating in Electric Kettle
-Heating element is encased in a metal tube -Heat is generated when current passes through heating element -Water surrounding the heating element gets heated and heat is transferred throughout the water by conduction and convection
Nichrome wire is used as heating element in electric iron and kettles
-Nichrome has high melting point -High density -does not oxidise easily
Earthing
-Protects user from electric shock if metal casing becomes live -The large current flows to the ground through the earth wire,as it has a much lower resistance than the person -Person no electric shock
Circuit breakers
-Safety devices that switch off the electrical supply when there is a overflow of current
Double insulation
-Substitute for earth wire -In addition to first insulation on wire, there is 2nd insulation
Fuse
-safety device that protect the equipments against excessive current flow -Fuse wire made up of tin-lead alloy that has a low melting point,when current becomes to large,fuse heats up and melt, cutting of the circuit -Fuse rating 1A,3A,5A,10A,13A -Fuse used should be slightly above current -Fuse connected to live wire,so that appliance wont become live after fuse blown
Electrical Hazards
Damaged insulation -live wire come in contact with metal casing Overheating of cables -insulation to melt,starting fires Damp conditions -electric shock
Formulas in practical electricity
E=VQ E is electrical energy (Joules) P=IV P is power (Watts)
Cost of electrical appliances
Measured in KWh *Make sure units are KW and hr
Wiring plug
Neutral Earth Live