Sustainable Living: 3M FuturewiseTown PlanIntroductionGo BackGo Next: Generating electricity3M

Energy types

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Efficiency of
energy changes

Energy transformations

Efficiency of energy transformations

Often when there is an energy transformation, some energy is converted into an
unwanted form e.g. heat in a mobile-phone charger. The more energy that ends up
in this unwanted from the less efficient the energy transformation has been.

If a transformation is 100% efficient then all the energy put into the system is output as
the desired form of energy. This never really happens! The closest to a 100% efficient
transformation is an almost near silent heater that gives out no light – in this case
nearly all the electrical energy is converted into heat energy.

Heat energy is not as useful because, once it is created, it is hard to change
into any other form of energy.

If an electric motor gives out 70J or kinetic energy for each 100J of electrical
energy put in, the motor is said to be 70% efficient. The equation is:

Efficiency = Useful energy out   x 100%   70% = 70   x 100%
     Total energy     
 
100

Find out how electricity is generated