# Active and Passive Elements of Electrical Circuit

## Active Elements of an Electric Circuit

**Active elements of an electrical circuit**are those elements which can continuously give as well as take energy to and from the circuit, respectively. Voltage Source:

A voltage source can be considered as an active element. If current leaves from the positive terminal of the voltage source, the energy is delivered from the source to the circuit.

On the other hand, if the current enters through the positive terminal of the voltage source, the energy is absorbed by the source. If the voltage source is considered as ideal, the terminal voltage the source is constant and it is intendant of the value of current it delivers to the circuit. But in practical voltage source, the terminal voltage of the source decreases with increase in current, it delivers to the circuit. This is because, there is a voltage drop in the source due to its internal resistance. Although the internal resistance of a practical voltage source is very small. So, the voltage of the practical source slightly depends upon the current.

As per definition of **active element of electrical circuit**, a battery can be considered as active element, as it continuously delivers energy to the circuit during discharging, and absorbs energy from the circuit continuously during charging of battery.

Current Source:

A current source is also considered as active element. The current supplied to the circuit by an ideal current source is independent of circuit voltage. In practical current source, as such there will be a high internal resistance connected in parallel with the source. The current supplied by the source is dependent on the circuit voltage based on the value of the internal resistance.

## Passive Elements of an Electric Circuit

**Passive elements of an electric circuit**are those elements which cannot deliver or absorb energy continuously. As per this definition, resistance, inductance and capacitance are taken as basic passive elements of an electric circuit. Resistor:

Resistor is taken as passive element since it can dissipate energy as heat as long as current flows through it but in any situation a resistor cannot deliver energy to the circuit. Resistance is the property of any substance by which it can resist the flow of current through it. An electrical conductor has very low resistance, whereas an insulator has very high electrical resistance. The unit of resistance is ohm, which can be represented by the symbol Ω.

Inductor:

An inductor is also considered as passive element of circuit, because it can store energy in it as magnetic field, and can deliver it to the circuit, but not in continuous basis. The energy absorbing and delivering capacity of an inductor are limited and transient in nature. That is why, an inductor is taken as passive element of a circuit.

Capacitor:

For same reason, a capacitor is considered as passive element, because it can store energy in it as electric field and deliver it to the circuit, but not in continuous basis. The energy dealing capacity of a capacitor is limited and transient too.

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