# Where to start?

Discussion in 'General Electronics Chat' started by Tripodial, Dec 3, 2012.

1. ### Tripodial Thread Starter New Member

Dec 3, 2012
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I've started studying electrical engineering, and I feel lost. I am interested in it, but I really don't get anything

For very simple tasks of node voltage method, Thevenin equivalent, source transformation etc., I get the correct answer, but as fast as they are a bit more advanced, I am completely lost at where to start, and I just try something, which always ends up being incorrect.

Here are 3 circuits I found after googling Thevenin equivalent, that I don't understand how to solve.

Also, I don't know how to solve matrices, so I use the substitution method to solve for 2-3 unknowns in, for example, node voltage tasks. How can I do this to be most sure not to miscalculate something? I very often do mistakes!

2. ### WBahn Moderator

Mar 31, 2012
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The main thing is to be sure that you thoroughly understand the fundamentals, namely things like what voltage is and what current is and how they relate to energy and power (and what the difference is between energy and power). Then you need to understand what KVL and KCL are in terms of these fundamental concepts. This means understanding why KVL is simply a statement of the conservation of energy in a conservative electric field and that KCL is simply a statement of the conservation of charge. Next you want a firm understanding of the passive sign convention, including what it is and why it is set up the way that it is. At that point, you are ready to start understanding (not memorizing, but understanding) the various analysis techniques such as node voltage and mesh current. With that understanding, you will be able to look at a circuit and see where parts of the circuit will cause difficulty (even if just through some additional steps that will be involved) for different techniques. For instance, because node voltage analysis is simply a formalized application of KCL, the presence of current sources can make thing a lot simpler while the presence of voltage sources has the potential to make thing more difficult since it can be hard to quantify the current in a voltage source in a simple way. We often get around this by using the notion of a supernode and, with an understanding of the fundamentals, you won't have to memorize how to set up and use a supernode, it will simply be an obvious way to get around the problem.

As for miscalculations, the best way is to take things in small chunks (i.e., don't try to do too many things in one step), track your units from beginning to end and actually check them, and try to estimate what the results should be, both at the end and at intermediate steps and always ask if the answer makes sense. Finally, don't just get an answer and settle for it -- check your work. Plug things back into the original rquations, total up the voltage and/or current in several places in the circuit, figure out if the total power consumed by the loads matches the total power supplied by the sources, etc., etc.

3. ### Tripodial Thread Starter New Member

Dec 3, 2012
2
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Thanks! I do understan KCL, KVL, what voltage is etc., it's mainly just to understand where to start in an advanced circuit that confuses me!