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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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