An electric current, when going through a circuit, can produce several effects: heat a conductor, generate chemical reactions in electrolytic conductors, move the needle of a compass near a circuit and many other effects. In the event that the current moves an real object, a mechanical work is performed. In the case of chemical reactions, a chemical work is performed. Remember that work is the process in which energy is transformed or transferred between systems. Therefore, it is important to understand the transformations involving energy, either electrical, thermal, mechanical or chemical.

## Energy and Electric Power

Important Definitions:

Power:
It is the energy transfer rate of a current to a device. For a current in a circuit section $$AB$$ , power is the work $$w_{AB}$$ which is carried by the current in a time interval $$\Delta t$$ . Equivalently, power is also the eletric potential, difference $$\mathbb{V}_{AB}$$, times the current intensity in the circuit section $$AB$$. Mathematically, we have: $$P = \frac{w_{AB}}{\Delta t} = i \mathbb{V}_{AB}.$$
Joule's Law:
The amount of heat dissipated in a conductor, through which an electric current is flowing, is directly proportional to: the resistance $$R$$, the square of the current $$i$$, and the time interval $$\Delta t$$ that the current lasts. That is, the amount of electric energy that is transformed into thermal energy is $$E = R i^2 \Delta t.$$
It is commonly used kilowatt-hour $$(kWh)$$ as the power unit. A kilowatt-hour is the amount of energy that is transferred in the time interval of $$1h$$ with power of $$1kW$$ , $$kWh = 3.6 \times 10^6 J = 3,600,000 J$$

### Characteristics of Electrical Appliances

It is common to find on electrical appliances their main electrical characteristics, that is, the electric power it consumes and the $$\mathbb{V}$$ that it must be connected on.