Circuit Elements - Active Passive Elements of Electrical CircuitPublished on 7/7/2017 & updated on 5/10/2018
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Circuit elements are those components of an electric circuit or electronic circuit which either can supply energy to the circuit or can take energy from the circuit. All the components of a circuit are connected together in required manner by conductors to form a desired and complete circuit. If the connecting conductor are taken as ideal, all the parts of the circuit, except the connecting conductors are circuit elements.
Types of Electric Circuit ElementsThe electrical circuit elements either absorb energy from circuit or deliver energy to the circuit. Based on that there are two types of electric circuit elements, namely passive circuit elements and active circuit elements.
Passive ElementThe circuit elements that receive energy (or absorb energy) and either convert it into heat or store it in an electric field or a magnetic field are called passive circuit elements.
ResistorResistor 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.
InductorAn inductor is also considered as passive element of circuit, because it can store energy in it as magnetic field, and can deliver that energy to the circuit, but not in continuous basis. The energy absorbing and delivering capacity of an inductor is limited and transient in nature. That is why an inductor is taken as a passive element of a circuit.
CapacitorFor same reason, a capacitor is considered as passive element, because it can store energy in it as electric field and delivers that energy to the circuit, but not in continuous basis. The energy dealing capacity of a capacitor is limited and transient too.
Active Circuit ElementThe circuit elements which supply energy to the circuit are called active circuit element.
Examples include voltage sources, current sources, and generators such as alternators, DC generators etc.
Voltage SourceA 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. 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.
Current SourceA current source is also considered as active element. The current supplied to the circuit by an ideal current source is independent of circuit voltage.
Note: A transistor is an active circuit element, because, it can amplify the power of a signal. On the other hand,transformer is not an active circuit element because it does not amplify power and the power remains same both in primary and secondary side. Although, a transistor is an example of active circuit elements, but the transformer is an example of passive circuit elements. The circuit elements can also be categorised as bilateral and unilateral.
Bilateral Circuit ElementConduction of current in both directions in a circuit element with same magnitude is termed as bilateral circuit element. It offers same resistance to the current of either directions.
Examples: Resistors, inductors, capacitors etc. This figure shows that a bilateral circuit element can conduct from both sides and offers same resistance for current from either side.
Unilateral Circuit ElementThe unilateral circuit element does not offer same resistance to the current of either direction. The resistance of the unilateral circuit element is different for forward current than that of reverse current.
Examples: diode, transistor etc. This figure shows, a diode as unilateral circuit element. When diode is forward biased it offers very small resistance and conducts. While it is reverse biased, it offers very high resistance and doesn't conduct. The circuit element can be categorized in another manner, such as lumped and distributed circuit elements.
Lumped Circuit ElementsWhen the voltage across and current through the element don't vary with dimension of the element, it is called lumped circuit elements.
Examples: Resistor connected in any electrical circuit.
Distributed Circuit ElementWhen the voltage across and current through the element change with dimensions of the element, it is called distributed circuit element.
Examples: Resistance of a transmission line. It varies with the length of the line.
Electrical Circuit SymbolAn electric circuit contains the symbol for every component and product. A circuit diagram uses symbols to represent parts of the circuit. If you want to read any circuit you should familiar with the entire electrical circuit symbol.
|DC Power Supply|
|Variable DC Power Supply|
|AC Power Supply|
|Potentiometer, Voltage Divider|
|Light Dependent Resistor (LDR)|
|Polarised Capacitor, Electrolytic Capacitor|
|Iron-cored Transformer (two Secondary Windings)|
|Light Emitting Diode (LED)|
|n-Type Junction Field Effect Transistor (NJFET)|
|p-Type Junction Field Effect Transistor (PJFET)|
|Integrated Circuits||Integrated Circuit (IC)|
|Cathode Ray Oscilloscope (CRO)|
|Operational Amplifier (Op-Amp)|
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