Physics

Electricity in the home

What is direct current (d.c.)?

Direct current

(

d.c

.) is an electric current that always flows in one direction.

Made by batteries. Electronic circuits such as those in computers and stereos need direct current electricity in order to work. Direct current cannot be transferred well over large distances.

What is alternating current (a.c.)?

Alternating current

(

a.c.

) is an electric current that is constantly changing direction .

produced by most generators and is used in mains electricity. Motors often work using alternating current. The voltage of alternating current is easily changed with a transformer. Alternating current can be transferred efficiently over large distances.

Which type of current – a.c. or d.c.?

Electricity supply to our homes • Voltage of 230 v a.c.

Plugs and electrical cable An electrical plug is inserted into a socket and the cable which is attached to the plug carries electricity to the appliance.

Inside an electrical cable

copper There are three wires

made out of

copper

Each wire is surrounded in

plastic

.

insulating plastic

Materials in a plug

The

live wire

carries a current from the mains supply to the applicance . It is brown The earth wire is a safety device that allows current to flow from the the appliance to plug if there is a fault in the appliance.

is green and yellow!

It The

neutral wire carries the current from the appliance to the mains supply. It is blue

What is a fuse?

A fuse is a safety device

When a large current flows the wire becomes hot. How does a fuse work?

melts which breaks the circuit.

terminals thin wire with high resistance case made of insulating material

How to wire a plug correctly • Open the plug • Connect live wire to the live pin with the fuse on it • Connect the neutral wire to the neutral pin • Connect the earth wire to the earth pin!

• Close the plug!

Plugs – true or false?

Power ratings • Power is the amount of energy used per unit time.

• Power is measured in watts.

High power rating • Things that use a lot of power e.g electric heater, dishwasher

Low power rating • Appliances that use a small amount of power E.g CD player 15 W power rating, computer 70 W

Paying for electricity in Ireland?

• It depends on how many units of energy used • Unit of energy used = kilowatt hour.

• A kilowatt hour = amount of energy needed for 1kW of power to be used for 1 hour.

Cost of electricity

cost = number of kilowatts x number of hours x cost per hour

Buying electricity problem A kettle has a power rating of 8 kW It is turned on for 5 hours.

If electricity costs 10 c per kilowatt hour how much does it cost to use the kettle?

Cost of electricity: cost = number of kW x number of hrs x cost per hr = 8kW x 5hrs x 10 c/ kWhr = 400c or 4 euro

A toaster has a power rating of 6 kW It is turned on for 3 hours.

If electricity costs 9 c per kilowatt hour how much does it cost to use the kettle?

Cost of electricity: cost = number of kW x number of hrs x cost per hr = 6kW x 3hrs x 9 c/ kWhr = 162c or 1 euro 62 cent