In science we learnt that electrical
energy is converted by domestic appliances into other
forms of energy, for example a television converts electrical
energy into sound energy and light energy, a kettle
converts electrical energy into heat energy, a light-bulb
converts electricity into light energy. We learnt that
energy is often wasted in these transformations, the
television and light-bulb both give off heat energy
that is not useful. The kettle’s heat energy is
useful but it may make a noise, which is a waste of
energy. Appliances that convert most of their electrical
energy into other useful forms of energy we call efficient,
those that waste lots of energy are called inefficient
The electrical energy that our appliances change into
other sorts of energy is called power. It is measured
in watts. If you look at electrical applicances at home,
you will see they are marked with a power rating in
watts. This tells you how many joules of energy the
appliance uses every second. The bigger the number the
faster the appliance uses energy. You may be asked to
work out the power of an appliance using this equation:
Power (watts) = current (amps) x voltage (volts).
We pay for electricity in units. In science we call
these kilowatt hours (1000 joules per second every hour).
We did calculations to see how many units different
appliances would use and how much and how much these
units would cost.
In another lesson we watched a video showing how in
the UK most of our electricity is generated a long way
from the cities that use it. We learnt that a lot of
power is wasted in the transmission of this electricity
and that heat that is a by-product of electricity generation
is lost into the atmosphere. We saw how in The Netherlands
and Denmark smaller power stations have been built within
cities. These save the waste of transmission over long
distances and allow the heat from electricity generation
to be used for central heating in nearby buildings.
These are called Combined Heat and Power stations.
We evaluated the pros and cons of electricity generated
by Nuclear Power and ‘Poo Power’ (human
waste).
Commentary for teachers
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