Electrical Circuit Elements

Electrical Circuit Elements can be 

• Linear or Non-Linear 
• Active or Passive 
• Unilateral or Bilateral 
• Time-Variant or Time-Invariant 

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1. Linear or Non-Linear 

   • Linear Elements: 

     V-I characteristics follows only one equation of straight line passing through origine. Examples : Resistors, Inductors, Capacitors and Gyrator

   • Non-Linear Elements: 

     Elements lacking any of the above mentioned characteristics for linear elements are Non-Linear Elements. Examples : Diodes, Transistors etc..

2. Active or Passive 

   • Active Elements: 

     Active circuit elements have capacity of enhancing the energy level of signal passing through it. Slope of V-I characteristics of such elements is negative OR any part of V-I characteristics of such elements lies in 2nd or/and 4th Quadrant Example : Vacuum Tubes, Transistors, Power Sources...

   • Passive Elements: 

     Passive elements can’t enhance the energy level of signals passing through it. Their V-I characteristics never touches 2nd of 4th quadrant. Example : Resistors, Capacitors, Inductors
   
   During discharging period energy storing elements like Capacitors and Inductors Behaves like Active Elements ( slope of their v-i characteristic becomes negative) but their overall V-I characteristic never touches 2nd or 4th quadrant ( if you start drawing V-I characteristic when stored energy of element is zero), So they are Passive Elements.

3. Unilateral or Bilateral 

   • Unilateral Elements: 

     If the magnitude of current passing through an element changes or affected due to changes in polarity of applied voltage, the element is Unilateral Element. Example : Diodes, Transistors, SCRs. . .

   • Bilateral Elements: 

     If the magnitude of current remains the same OR if V-I characterises of an element remains unchanged OR if the element offers same impedance ——>> even if the polarity of applied voltage is reversed then it is a Bilateral Element Example : All linear elements.

4. Time-Variant or Time-Invariant 

• Time-Variant Elements: 

  V-I characteristic changes with time.

• Time-Variant Elements: 

  V-I characteristics remains same for all time.

Reference Books :