2)ELECTRICAL QUANTITIES

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ELECTRICAL RESISTANCE: OHM'S LAW
The resistance(R) of a material is equal to the voltage divided by the intensity of electric current which travels through the material. This ratio, which is called Ohm's Law, can be expressed as follows:
                                                         R=V/I
Ohm's law have other two forms:
                                           V=R*I          I=V/R
ELECTRICAL ENERGY AND POWER
Electrical energy
If a electric current(I) flows at a particular tension(V) for a certain amount of time(t), we can calculate the energy (E) that is consumed: E=V*I*t
In the SI, this electrical energy is measured in joules(J).
Electric power
The electric power of a load is the amount of energy that it can transform over a certain amount of time.Electric power is measured in watts(W) or kilowatts(kW).
If a electric current(I) flows at a particular tension(V), we can calculate the power(P) that is consumed:
                                                  P=V*I
The electrical energy that is consumed can be expressed as a function of power and time, using the kilowatt per hour(kW/h) as a unit of measurement.
If we know the power of a load, we can calculate the electrical energy that it consumes over a certain amount of time. We simply multiply the power in kilowatts by the amount of time in hours.
                                                                       E=P*T