# Ideal Sources Interconnection

Discussion in 'Homework Help' started by yan500, Sep 25, 2011.

1. ### yan500 Thread Starter Member

Jul 12, 2011
48
0
Hey guys, I have a quick question on the validity of the connections of these ideal sources. In the first picture, I don't understand why the connection is invalid. How would I go about tackling this problem if it were on a test?

In the second picture, the circuit is valid from a connection perspective but is not when you do some power accounting. I don't understand how it is valid with its connections.

Any help is much appreciated.

2. ### steveb Senior Member

Jul 3, 2008
2,433
469
As a first step in studying this subject, start with the simplest rules first. Ideal voltage sources should never be in parallel and ideal current sources should never be in series.

Why? Because ideal sources force a constraint that can not be violated. Since current in a series circuit is the same and voltage in a parallel circuit is the same, using two sources is stupid because you can't have two different numbers equal to each other. If both sources are the same value, then you can't resolve how much power is delivered from each source, so it's at best redundant and at worst unresolvable, depending on your point of view.

Extending to more complicated circuits, the general rule is that you should not end up with contradictory constraints, nor unresolvable voltages, currents or powers.

So the first problem is simple now, right?

yan500 likes this.
3. ### yan500 Thread Starter Member

Jul 12, 2011
48
0
Ah, I understand now. That does seem rather silly to have parallel voltage sources. Thank you so much, I wish my textbook's explanation was as clear as yours.