# Homework Help: Kirchoff rule

1. Aug 18, 2011

### soupastupid

1. The problem statement, all variables and given/known data
write two independent equations using kirchoff rule to describe the circuit.

2. Relevant equations

V=IR
Emf = IR

3. The attempt at a solution

emf2 -I1R3-I2R2-I1R1 = 0
(ok i have questions here: why is it I1R1? shouldnt it be I4R1?)
and
emf1-I3R2+I2R2 = 0

(my question here is why is it +I2R2, why wouldnt u put -I2R2? or does it depend on which way you set up current through R2?)

#### Attached Files:

• ###### kirchoffruel.jpg
File size:
15.8 KB
Views:
126
Last edited: Aug 18, 2011
2. Aug 18, 2011

### cepheid

Staff Emeritus
There is no I4 that I can see. In any case, R1, emf2, and R3 are all in series, so the current has to be the same through all of them (and that current is I1 in this diagram)

When you go around the loop, you're moving across the resistor from bottom to top, which is the opposite direction from the direction of the current through that resistor. The current flows from top to bottom, which means that the top side is more positive than the bottom side. So if you move from bottom to top, you gain voltage.