Why does the supernode analysis work?

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drcne

Joined Aug 3, 2017
15
I'm having a hard time understanding when and why can you use supernode analysis. My book doesn't really explain it, it just states that it's something you can do, and that a supernode doesn't have a voltage of it's own even though it contains a voltage source. Any help would really be appreciated, thanks!

EDIT: Actually I just figured out why you can use a supernode; however, I am still confused about the statement "a supernode has no voltage of it's own". How can this be true if it contains a voltage source?
 
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MrAl

Joined Jun 17, 2014
7,581
I'm having a hard time understanding when and why can you use supernode analysis. My book doesn't really explain it, it just states that it's something you can do, and that a supernode doesn't have a voltage of it's own even though it contains a voltage source. Any help would really be appreciated, thanks!

EDIT: Actually I just figured out why you can use a supernode; however, I am still confused about the statement "a supernode has no voltage of it's own". How can this be true if it contains a voltage source?

Hi,

The simple answer is that a theorectical short circuit can be either a real short or a special kind of electronic short.

A real short is where the current is allowed to flow through the short as is governed by the external parts of the circuit, and the voltage is reduced to exactly zero. So it is a short for both current and voltage.

A special kind of short is one where we still allow the current to flow as in a real short, but we do not change the theoretical voltage so both the current and voltage are dependent on the external circuit conditions. So it is a short for current but not for voltage.

We might want to call this phenomenon an aniselectro short or some other descriptive name, which implies that the properties are different depending on how we measure it. That would make a general short circuit an aniselectro short and from there we would determine which one we need to use depending on the situation at hand.
 

WBahn

Joined Mar 31, 2012
25,740
I'm having a hard time understanding when and why can you use supernode analysis. My book doesn't really explain it, it just states that it's something you can do, and that a supernode doesn't have a voltage of it's own even though it contains a voltage source. Any help would really be appreciated, thanks!

EDIT: Actually I just figured out why you can use a supernode; however, I am still confused about the statement "a supernode has no voltage of it's own". How can this be true if it contains a voltage source?
It doesn't have a voltage of its own because it is more than a single node and each node that makes up the supernode has a different voltage (at least symbolically). What you have are constraints between the voltages at the various ports of the supernode imposed by the sources within it.
 
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