Efficiency is an important consideration in any transducer. Transducer efficiency is defined as the ratio of the power output in the desired form to the total power input. Mathematically, if
\[P_{IN}\]
represents the total power input and \[P_{OUT}\]
represents the power output in the desired form, then the efficiency is \[E=\frac{P_{OUT}}{P_{IN}}\]
No transducer is 100 percent efficient. Energy is always lost to electrical resistance as heat. Usually this loss is manifested in the form of heat. Some transducers are very efficient - aerials can be 80 - 90% efficient - but old style light bulbs are very inefficient - maybe only 20%