The Thevenin and Norton theorems are useful ways to simplify circuits, but they have some problems when we deal with non-linear circuit parts. Let’s break it down:

1. Linear vs. Non-Linear:

   • These theorems work based on the idea of superposition. This means they’re only helpful with linear elements like resistors, capacitors, and inductors.
   • Non-linear parts, like diodes or transistors, behave differently. Their properties change based on the voltage or current, which makes things more complicated.

2. When to Use Them:

   • If a circuit has non-linear elements, you usually can’t use Thevenin or Norton directly.
   • Instead, you sometimes need to find the circuit's operating point. This often involves using piecewise linear approximations, which helps you analyze it around that specific point to get an equivalent linear circuit.

3. Practical Challenges:

   • This means more work for you! You will often need to use numerical methods or simulations to accurately study these types of circuits.
   • While this can take extra time, it’s important for understanding how the circuits really work.

In short, Thevenin and Norton theorems are powerful tools. However, they don’t work as well with non-linear elements and need some extra steps to help analyze these circuits accurately.