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Mains Electricity - Bills.

If you look at a domestic electricity bill for a 3 month
period,

you will see that there are two meter
readings.
One is the

present reading and the other is the previous (last) reading.

Subtracting the previous reading from the present reading

gives the number of units used in that 3 month
period.

Electricity is priced
in pence per
unit.

Multiplying the number of units used by the price per unit

gives the cost of electricity for that
period.

Other
costs may include VAT
and the standing charge.

The standing charge is a fixed cost that is
paid for the

convenience of being connected to the electricity supply.

VAT is a tax collected by the government.

What is a kilowatt-hour?

One unit of electricity
is 1kWh (one kilowatt-hour).

kilo means thousand, so one kilowatt is 1000 watts.

One kilowatt-hour is
the amount of electricity

used by a
1000 watt appliance running for 1
hour.

1
watt is 1 joule per
second, 1000 W = 1000 J per s.

1
hour = 60 x 60
seconds, = 3600 seconds.

Therefore, 1kWh = 1000 x 3600 joules,

= 3,600,000
joules of
energy.

Note that a kWh is a unit of energy, not power.

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