Is a Transistor Considered a Fundamental Circuit Element?

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Discussion Overview

The discussion revolves around the classification of circuit elements, specifically whether a transistor qualifies as a fundamental circuit element. Participants explore definitions of fundamental elements and the implications of modeling components in electrical circuits.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant questions the definition of a fundamental circuit element and suggests that a switch may be considered a fundamental element or a resistor with infinite resistance.
  • Another participant argues that fundamental elements are unique and cannot be subdivided, asserting that resistors, capacitors, and inductors are fundamental, while transistors can be modeled using these elements.
  • A different viewpoint introduces the concept of equivalent circuits, noting that while transistors can be represented by fundamental elements, these representations are fictional and not physically realizable.
  • It is noted that no pure resistor or circuit element can exist without physical properties that introduce inductance and capacitance, complicating the notion of fundamental elements.
  • Participants discuss the necessity of making assumptions in modeling systems, such as neglecting inductance and capacitance in certain applications like electric heaters.
  • One participant emphasizes the importance of practical engineering judgment in deciding what elements to neglect in circuit analysis.

Areas of Agreement / Disagreement

Participants express differing views on the classification of transistors and other circuit elements as fundamental. There is no consensus on the definitions or implications of these classifications, indicating ongoing debate.

Contextual Notes

Participants highlight limitations in the practical realization of fundamental circuit elements and the assumptions made in modeling, which may affect the analysis of circuits.

SpartanG345
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How do you define what is a fundamental circuit element? I am not really sure, why isn't a transistor a fundamental circuit element.

Can u consider a switch a fundamental circuit element or is it a resistor with infinite resistance.
 
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The term "fundamental" itself expresses the meaning that it is unique and not be subdivided into other simple elements. Resistor, capacitor and inductor are fundamental circuit elements, while transistor is not, because a transistor can be modeled/visualized in terms of the fundamental elements shown above. Regarding switch, you yourself mentioned that it is resistor with infinite resistance, which means that you are able to decompose itself (switch) into further simple (fundamental) element (in this case it is resistor) and hence it is not a fundamental element
 
It doesn't do to get too hung up on terminology.
When I was very young I came across the idea of the 'equivalent circuit' of a transistor. This involved the notion of replacing an actual transistor with a circuit consisting of 'fundamental' and ideal resistors, capacitors and current sources with fictitious characteristics. This equivalent circuit, if you could actually build it, would behave like a transistor but it is only a fiction which is used to gain an understanding of the actual behaviour of a transistor. I worried a lot about this at the time because I hadn't actually ever got as far as designing a circuit containing a transistor. I really thought you could build one.
Another, easier, example I came across was the equivalent circuit of a battery (an ideal emf in series with a small resistor - the internal resistance).
Those were both examples in which you can say we use "fundamental" elements but, in neither case, can you pick up and handle any of these elements. A pure resistor can't exist because it will have physical size and, hence, will have inductive and capacitative qualities. The same goes for every other circuit element you can think of.
 
As mentioned here
sophiecentaur said:
A pure resistor can't exist because it will have physical size and, hence, will have inductive and capacitative qualities. The same goes for every other circuit element you can think of.

it is impossible to see an individual fundamental circuit element in practice. Yet we have to make some assumptions to model the system for analysis. If I have to model an electric heater, it is obviously not wrong to neglect its inductance and capacitance.
The central idea is to find the basis at which every thing else can be expressed in an acceptable approximate sense.
 
That's where you need to be wearing your Engineer's hat and know what to neglect.
 

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