Efficiency or mechanical efficiency of machine is the ratio of effectiveness of the machine to the input provided to it. With the help of mechanical efficiency, it is determined how much advantageous is the machine for production. Remember, the value of efficiency is less than unity for effective machines.


Mechanical Efficiency, ηm =(Output )/Input


ηm =(Work Output )/(Work Input)

=(Power Output )/(Power Input)


Work Output = Work Input – Energy Losses

Substituting the same in the above equation, we get-

ηm =(Work Input-Energy Losses)/(Work Input)

= 1 – (Energy Losses)/(Work Input)                (Energy Losses > 0)


ηm< 1

Electrical Efficiency of Machine:

The electrical efficiency of a machine can be defined as the ratio of energy consumed by the machine to produce useful work to the total energy supplied to it in the form of electricity.

Mathematically, it can be written as-

Electrical Efficiency, ηe =(Useful Power Output )/(Total Power Input)

Thermal Efficiency:

The thermal efficiency of a machine can be defined as the ratio of output of energy that actually utilizes for final production to consumption of total energy by the machine.

Mathematically, it can be written as-

Thermal Efficiency, ηt =  (Benefit )/Cost

Considering the thermal efficiency of a machine, its value falls in range

0 t< 1

Overall Efficiency:

The overall efficiency of a machine is simply the product of all the available efficiencies of a machine to determine its effectiveness. In other words, the product of mechanical efficiency, electrical efficiency and thermal efficiency is called overall efficiency of machine.

Mathematically, it can be written as-

Overall Efficiency, ηo    = Mechanical Efficiency x Electrical Efficiency x Thermal Efficiency
= ηmx ηe x ηt


Mechanical Advantage:

Mechanical Advantage or MA is the ratio of force produced to the force applied to a machine. This determines the performance of the machine.


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