# Parallel voltage sources circuit

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So now I want to find Vcd

So!

Vc -> 0

(I can do that, right? Set Vc as my zero point, since it makes things easier)

Vcd = I2 x 0.5 - I3 x 4 = 8.615 x 0.5 - 2.077 x 4 = -4 V

Yes? Wow! You're starting to make up your own exercises! Cool! Well, let's see....
You followed the wire down and back up.

Can you also follow the wire up and then back down?

(As for setting Vc to zero. I guess that's fine, although I wouldn't write it down.)

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Wow! You're starting to make up your own exercises! Cool!

Well, let's see....
You followed the wire down and back up.

Can you also follow the wire up and then back down?
Vcd = 6 - 10 = -4V

w00t :D

(As for setting Vc to zero. I guess that's fine, although I wouldn't write it down.)
Why wouldn't you?

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Why wouldn't you?
Well, suppose you set Vc to zero because you want to calculate Vcd.

And then you set Va to zero because you want to calculate Vab.

But now... you have set both Va and Vc to zero, which can't both be true!

You can use it as a trick in your mind to find Vcd, but Vc does not really have to be 0 [V].
Especially not if there is a ground attached to some other point of the circuit.

Gold Member
Well, suppose you set Vc to zero because you want to calculate Vcd.

And then you set Va to zero because you want to calculate Vab.

But now... you have set both Va and Vc to zero, which can't both be true!
Well I don't have to use the fact that Vc = 0 anymore when I look for ab.

I can write IF Vc = 0 then Vcd equals...

And then at the other clause I write

IF Va = 0 then Vab equals....

Especially not if there is a ground attached to some other point of the circuit.
If there is a ground, I have to use the ground they give me, right? As of now, it's kind of a groundless circuit

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Well I don't have to use the fact that Vc = 0 anymore when I look for ab.

I can write IF Vc = 0 then Vcd equals...

And then at the other clause I write

IF Va = 0 then Vab equals....
The problem with those statements is, that Vcd will still equal whatever you calculated, even if Vc is not zero (since Vcd is a "difference").

If there is a ground, I have to use the ground they give me, right? As of now, it's kind of a groundless circuit
Yes. It's groundless.

Gold Member
Yes. It's groundless.
Is this like our "circuit flowing in space" idea? Not connected to ANYTHING!

The problem with those statements is, that Vcd will still equal whatever you calculated, even if Vc is not zero (since Vcd is a "difference").
So in other words I don't have to define anything as my "zero" point. Duly noted!