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Fundamental circuit element

  1. May 16, 2010 #1
    How do you define what is a fundamental circuit element? I am not realy 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.
     
  2. jcsd
  3. May 17, 2010 #2
    The term "fundamental" itself expresses the meaning that it is unique and not be subdivided in to 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) in to further simple (fundamental) element (in this case it is resistor) and hence it is not a fundamental element
     
  4. May 17, 2010 #3

    sophiecentaur

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    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.
     
  5. May 17, 2010 #4
    As mentioned here
    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.
     
  6. May 17, 2010 #5

    sophiecentaur

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    That's where you need to be wearing your Engineer's hat and know what to neglect.
     
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