The energy in physics is a scalar quantity typifies closed systems, which is constant in every transform in time.

The conversation of energy “It does not appear, but transform”-> during the interaction the more the one participant energy increases, the more the other participant energy decreases.

The power Typify the speed of the transforms. Mark: P-> speed=>

P= dE/dt = alteration/ elapsed time

Its measure is Watt (1000W= 1 kW, 1000000W= 1MW). 1 W means: 1 J alteration done in 1 s. 1W= 1 J/s
     For example a power station’s power means, how much energy it generate in a unit of time.

The efficacy It typifies the thrift of the process. It shows the rate of the beneficial invested energy and the total energy. It is a rate that is why it doesn’t have measure.
n=DEn /DEö       d=delta-> means transfiguration.

The beneficial changing of energy is always than the total changing of energy that is why the efficacy can be 100% only in idealized case.
n max.1. (n- the mark of efficacy)

We are going to see efficacy in power stations. It is worthwhile to run a power station if it generates more energy than it needs for the work. That is why pays to build a nuclear power plan; it generates much energy with small investment.

Curious thingsThe bill for electricity must be paid by right of consumerism. It shows how much energy chop existence in a unit of time. This quantum measured in kilowatt-hour. From P= DE/Dt=>DE=PDt=> By this the measure of kwh can be constituted that is equal to the energy chop that is procreated in one hour by a one-kW-power apparatus.