5.8 Efficiency
The efficiency of a working system tells us what part of the energy can be converted into the required useful form of energy and what part is wasted out of the energy available.
The available energy for conversion is usually called the input energy, and the energy converted into the required form is known as the output energy.
lightbulbThe efficiency of a system is defined as the ratio of useful output energy to the total input energy.
Efficiency = Useful output energy / Total input energy
Efficiency is often multiplied by 100 to give percentage efficiency:
Percentage Efficiency = (Useful output energy / Total input energy) × 100
It can also be given as:
Percentage Efficiency = (Useful power output / Total power input) × 100 ............ (5.6)
It is found that the energy output is always less than the energy input. During any conversion of energy, some energy is wasted in the form of heat. No device has yet been invented that may convert all the input energy into required output. That is why a system cannot have an efficiency of 100%. As energy losses are inevitable in the working of a machine, an ideal or perpetual machine cannot be constructed.
lightbulbFor Your Information! A machine with its output equal to input is called an ideal machine with efficiency 100%.