How Does Kirchhoff's Law Apply to Calculating Currents and Voltage Differences?

[SammyS]

For the same reason that any other wrong answer is wrong.

There is no reason the answer should be 12V - 8V.

 

[flyingpig]

But was my guess at what the answer really should have been right when you hinted at me? That it is the voltage drop across the 2Ω resistor because the 2Ω resistor is the only resistor in the intersection of the loop?

 

[SammyS]

But was my guess at what the answer really should have been right when you hinted at me? That it is the voltage drop across the 2Ω resistor because the 2Ω resistor is the only resistor in the intersection of the loop?

Yes.

As long as you got I_a & I_b right.

 

[flyingpig]

Sammy, the solutions posted said the voltage drop is -1.80V

Here is my question, when we tackle these problems, aren't we only concerned with the magnitude?

 

[SammyS]

Sammy, the solutions posted said the voltage drop is -1.80V

Here is my question, when we tackle these problems, aren't we only concerned with the magnitude?

No. Among other things, the sign has to do with which way the current flows.

 

[flyingpig]

Then how do I know that it is -1.80V?

 

[SammyS]

The sign will depend upon whether they found V_a - V_b or V_b - V_a.

 

[flyingpig]

So it is not unique?