# How to know the efficiency?

Efficiency (Efficiency) is one of the most important characteristics of machines, mechanisms, devices, systems, where the processes associated with the transfer or conversion of energy. Therefore, before using a device, its efficiency is calculated in order to evaluate the effectiveness of its possible use. We will talk about how to find out the efficiency, by what formula this parameter is calculated and how science determines it.

How to know the efficiency? Efficiency is the ratio of useful work to full work. For convenience, the result is multiplied by 100 and get a response in percent.

The formula for calculating the efficiency, which is usually denoted by the Greek letter η ("this"), is written as follows:

- η = (Auseful/ Afull) * 100%, where A is work.

For example, to raise the load to a certain height, you need to perform useful work. Anduseful= 5000 J. To lift the same load using the elevator to the same height, you need to do a full jobAfull= 8000 j.

Thus, the efficiency of the elevator is:

- η = (Auseful/ Afull) * 100% = (5000 J / 8000 J) * 100% = 62.5%

Also, efficiency is sometimes defined as the ratio of the power given by the mechanism to the power supplied to it or the ratio of the useful energy to the total energy received by the system.

Since part of the complete work of the machine is spent on heating its parts, on fighting the forces of friction and resistance and other needs, the work at the exit or the useful work always turns out to be less than the total work. Thus, the efficiency can not be more than 100%.

For example, the efficiency of an internal combustion engine is 20–40%, a steam turbine — 30%, an electric motor — up to 98%.

Many people are interested to know their efficiency, that is, the devices they use. Often for this purpose it is not necessary to carry out calculations, and it is enough to glance in the technical passport of the mechanism.

Sometimes the concept of efficiency is used to describe the performance of the person. But how to find out your efficiency? Of course, we are not talking here about numbers, but only about such values as “high” or “low”. To do this, compare the end result of any work with the effort expended, compare the results of the comparison with similar activities of other people or yourself at another time.

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