Understanding Kirchhoff's Circuit Problem: Finding Currents in a Complex Circuit

[Boulderbison19]

Homework Statement

Determine the magnitude and directions of the currents through r1 and r2 in the diagram below.

Homework Equations

V=IR

here is the schematic, i hope you can get the idea of the circuit from it:

The Attempt at a Solution

so i found the current through r2 to be -.4 Amps, which was the answer given using:

V=IR
6.0=15I

but i don't know if i just got lucky.

the answers given were I1=.68 amps and I2= -.4 amps. i am completely stuck on all of these kirchhoffs circuit problems, so any help will be much apreciated!

 

[marcusl]

Kirchoff's Laws require you to sum the currents into each node or sum the voltages around each loop. To do the voltage law, call I1 the current circulating, say, CW around the top loop (9V battery, R1, R2, back to battery) and I2 the current circulating around the bottom loop. The voltages around the top loop are

-9 + 22*I1 + 15*(I1-I2) =0

Do you see how that works? Now you do the bottom loop. Then it is a simple matter to solve for the currents I1 and I2.

BTW, are you at CU? Just wondering from your screen name...

 

[Boulderbison19]

thanks so much! that makes a lot more sense now. i couldn't figure out the paths, and tried almost everything.

i am at boulder high, just down the street.

 

[marcusl]

Good, glad to help

I'm south nearer Fairview.