# Homework Help: Kirchhoff's Laws

1. Jan 18, 2014

### frazdaz

1. The problem statement, all variables and given/known data

2. Relevant equations

$$\sum I_{in} = \sum I_{out}$$
$$\sum \epsilon = \sum pd$$

3. The attempt at a solution

Can anyone identify any mistakes in these? Probably signs

$$I = I_1 + I_2$$
$$12=4I_1 +3I$$
$$5=4I_1 - 2I_2$$
$$12-5=2I_2+3I$$

2. Jan 18, 2014

### BvU

What lets you think there are any mistakes ?

3. Jan 18, 2014

### frazdaz

The answers have I1 and I2 with opposite signs. I get them both as positive.

4. Jan 18, 2014

### Staff: Mentor

I make all currents positive for the directions shown.

I'm not sure what is achieved by that + sign accompanying each current arrow? It seems superfluous if it duplicates the function of the arrowhead, and just clutters the diagram.

5. Jan 19, 2014

### frazdaz

Well that's good news. And, yeah, I guess it's just intended to help with the maths side of things.