Resistor, Inductor, Capacitor - These are the three passive elements in an electrical circuit.
An electric circuit consists of active elements and passive elements.
- An active element supplies energy to the circuit.
- They control the flow of charges in a circuit.
- Active elements need power to operate.
- Examples of active elements are voltage source, current source, generator, transistor.
- A passive element receives electrical energy.
- They absorb, dissipate or store energy.
- Passive elements do not need power to operate.
- Examples are resistor, inductor, capacitor, diode, transformer.
Resistor
Resistor is a device that has resistance. Resistance means the ability to offer opposition to the flow of current through it. The resistor is made of a material that has a fixed amount of resistance, and has two leads to connect to the circuit. It dissipates the electrical energy it receives, in the form of heat.
The resistance of a resistor is measured in ohms. The resistance of an element is the ratio of potential difference across it to the current flowing through it. We know this as the Ohm’s Law.
Inductor
Inductor is a device that has inductance property. This device is in the form of a coil. It stores electrical energy in the form of magnetic field.
Inductance is the property of an element to induce electromotive force (emf) due to change in current through it. Inductance is defined as the ratio of emf generated to the rate of change of current through it. It is designated by the letter L, and its SI unit is henry (H).
Capacitor
Capacitor is a device that has capacitance property. This device contains two leads with an insulator between them. It stores electrical energy in the form of electrostatic field.
Capacitance is the property of an element to induce current due to change in voltage across it. Capacitance is defined as the ratio of current to the rate of change of voltage through it. It is designated by the letter C, and its SI unit it farad (F).
Frequently Asked Questions (FAQs)
Why is transistor considered an active element?
A transistor does amplification of the signal applied to it. Since power level is changed by the transistor, it is considered as an active element.
Why is diode a passive element?
A diode does not change power levels. It does not need a voltage source to operate.
Why is transformer considered as a passive element when it varies voltage and current levels?
Though a transformer varies voltage and current levels, the power levels at the primary side and the secondary side remain the same. It does not need a voltage source to operate.
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