25/02/2013
Energy Transformations
Energy cannot be created or destroyed (during
an energy transformation), but it can be
degraded.
That means that there is less useful energy
after a change than there was before.
This is because some of the original energy
has been changed into heat, which is then lost
to the surroundings.
Efficiency
Efficiency
energy output
=
J
x 100%
energy input
J
Efficiency =
power output
power input
W
x 100%
W
Efficiency
Worked Example
What is the efficiency of a water heater (rated
2kW) which is measured to produce 420J of
energy each second?
Efficiency =
Efficiency =
energy output
energy input
420
2000
x 100%
x 100% = 21%
1