Electricity at HomeGCSE Physics pg 134

Aims of the lesson

• Recall how to construct a circuit with multiple switches controlling an electrical device

Two-way switch

Leads

Bulb

Battery

Draw the circuit into your note book-

Aims of the lesson

• Understand how a financial bill for electrical energy is calculatedelectrical energy is calculated for a home

• State the unitunit for domestic electrical energy

• Solve simple problemssimple problems related to domestic electricity

Paying for Electricity• Under the stairs you will find…

kWh = kiloWatt Hour

29581 Units used

The Electric MeterThe Electric Meter

Paying for ElectricityAt my house 29 851 kiloWatt hour units

of electricity have been used

1 kWh

1 000

Joule per second

3 600 seconds

1 kWh = 3 600 000 Joules

29 851 kWh = 107 463 600 000 Joules

Paying for Electricity (pg 140)• The electrical energy we use at home is

measured in kiloWatt hours (kWh)(kWh)

• If ten 100 W light bulbs are on for one hour then 1 kWh of energy will be transferred

• 1 kWh is referred to as ‘one unit of domestic energy’

What do you get if you sit under a cow?

A pat on the head…

Finding out how much you owe…

5 4 9 6 8

2 0 5 4 8

10 / 7 / 2009

25 / 8 / 2009

120 Watts

40 Watts

40 Watts

On for 2 ½ hours

Electrical UnitsThe number of electrical units used is

calculated by-

The present meter reading minus previous meter reading

Or…

The power rating of an appliance (in kW) multiplied by the time it is on (in hours)

Paying for ElectricityThe price of the electricity is then

worked out using-

Pg 142- Questions 41, 42 and 43

Total cost = Number of units used x Cost per Unit

Set by the Government

Cost of Electricity• When paying for electricity one unit

is the same as 1000 Watts of energy being used in one hour.

• If a 60 W bulb is on for 4 hours then this is the equivalent of

60 / 1000 x 4 = 0.24 units

= 0.24 kWh

Aims of the lesson

• Recall some of the safety features of electricity in the home

• Recognise the three-pin plug• State the function of a fuse• Recall how to select a fuse for an

electrical appliance

Earth

Live

Neutral

Earth Wire

Connecting block

Fuse

Live Wire

Neutral Wire

Cable Grip

Insulation

Screw

Fuse holder

Pg 138- Wiring a Three Pin Plug

Electrical Safety• It’s not big and it’s not clever…

based on actual events…

It’s for your own protection…• The Fuse

Page 138

A fuse that ‘blows’ has broken the circuit because too much current has over-heated and melted the tiny wire within the fuse.

Which Fuse to Use?• Selecting the correct fusePage 139The Power Rating and Voltage of a device

will always be stated. Usually the voltage is 230 V.

e.g. For an electrical jigsaw with a power rating of 460 W

P = I x V460 = I x 230I = 460 / 230

I = 2 A

P I V to the rescue!

Use a fuse just above 2 A, possibly

a 3 A fuse

Question Time• Page 142

Attempt questions 39 and 40

Aims of the lesson

• Recall some of the safety features of electricity in the home

• State the difference between AC and DC electricity

An electrical fault (1)

An electrical fault (2)

Earth wire

Electricity at Homehttp://www.absorblearning.com/media/item.action?quick=73#

Electricity at Home

Direct current (d.c.)

Alternating current (a.c.)