Receptors are divided in two types.

Passive Receptors

These receptors transform electricity only into heat. Examples of passive receptors: resistors, electric showers, electric heaters etc.

Active Receptors

They transform electrical energy into another form of energy beyond thermal. It is important to remember that it is inevitable that any electric device generates heat, and some of the energy given to the device are lost. Examples of active receptors: electric motors, lamps, multimeters, computers etc.

Unlike a generator, which creates a potential difference called electromotive "force", a receptor has a "force" against electromotive "force" .

Counter Electromotive Force \((\varepsilon)\):

Counter electromotive force is the energy received by the receptor to be completely converted into another form of energy, other than heat. The \(\varepsilon\) is a decrease in the electric potential when the current passes through the receptor.

For historical reasons the term "force" appears in the name of this quantity, but it is just a potential drop, and it is measured in volts (V).

Receptor Power

Power Loss \((P_d)\):

Electrical power is wasted by the receiver, because it has an internal resistance \(r\) (internal dissipation). It means the amount of energy in Joules per second that are consumed uselessly into the receiver. Mathematically: $$P_d = ri^2.$$

Net Power \((P_n)\):

It is the electrical power that the receiver effectively converts in non-thermal power. It means the amount of Joules per second are converted into non-thermal energy. $$ P_n = \varepsilon i$$

Total Power \((P_T)\) :

It is the sum of the power dissipated and the useful power: $$ P_T = P_n + P_d = \varepsilon i + ri^2$$ where \(r\) is the internal resistance of the receiver.