Confusion with Kirchhoff's Law in Circuit Diagram

[jforce93]

Homework Statement

I have this circuit diagram (see attached), and the question is: Which of the following equations is Kirchhoff's first rule as applied to the above circuit?
With the answers:
I1 + I2 + I3 = 0
I1 - I2 + I3 = 0
I1 + I2 - I3 = 0
I1 - I2 - I3 = 0
(it's multiple choice)
The

Homework Equations

sum of I_in = sum of I _out

The Attempt at a Solution

I can't even begin. I understand Kirchoff's laws pretty well, but it just appears to me that the circuit is drawn wrong.

What am I doing wrong?

 

[gneill]

It seems that your attached diagram isn't attached

 

[jforce93]

It seems that your attached diagram isn't attached

Now it is

 

[kuruman]

Apply the equation that you posted. What is the sum of currents going in? What is the sum of currents coming out? Look at your drawing.

 

[gneill]

I see that the diagram has the currents labeled on each branch. Why don't you add some more such arrows nearer the nodes where the currents come together or diverge? Note that the current in any given series connected branch is always the same current!

 

[jforce93]

Apply the equation that you posted. What is the sum of currents going in? What is the sum of currents coming out? Look at your drawing.

I see part of it, but shouldn't the current in I₃ flow the other direction?

 

[gneill]

I see part of it, but shouldn't the current in I₃ flow the other direction?

Whether the actual current flows in the other direction or not does not matter; it simply means that when the equations are solved and calculations are completed with the assumed direction, it will yield a negative value for that current.

Take the assumed directions as given and write the equation from them.

 

[jforce93]

Whether the actual current flows in the other direction or not does not matter; it simply means that when the equations are solved and calculations are completed with the assumed direction, it will yield a negative value for that current.

Take the assumed directions as given and write the equation from them.

okay, thanks