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Definition of Linear Circuit? 
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#1
Mar1612, 12:55 AM

P: 28

1. The problem statement, all variables and given/known data
In the Lectures, we are told that techniques like homogeneity and superposition work only for linear circuits, but in Chapter 3 of the Textbook (which is the only place I can find one) I see a definition of linearity as "A circuit is linear if and only if 2. Relevant equations f(ax1 + bx2) = af(x1) + bf(x2)" i.e. if homogeneity and superposition work for it. 3. The attempt at a solution How do I tell, when confronted with an arbitrary circuit, whether or not it is linear  whether or not homogeneity and superposition are going to work for it? 


#2
Mar1612, 03:41 AM

HW Helper
Thanks
PF Gold
P: 4,856

No circuit is purely linear. Even R's and C's have voltagevarying iV characteristics. Obviously, a linear model works very well in almost all instances.
Transistor circuits are less linear: usually a linear approximation is made, like an equivalent circuit, constant beta, zero di/dV_{ce} in the linear mode, etc. Diodes are clearly nonlinear, since they conduct in one direction but not the other. Zeners are in the same category: their iV relationships are highly nonlinear. Photodiodes are amazingly linear, providing nearly constant di/dI over as many as 5 orders of magnitude (100,000 to 1). I = intensity. Got any other devices in mind? 


#3
Mar1612, 05:01 AM

P: 28

This apply only with LINEAR ELEMENTS in circuit. In fact, only independent sources, lineardependent sources and resistors are allowed.



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