# Current and Power in DC Circuits

I have two problems that have been bothering me, which I just cannot seem to figure out. Both have to do with current in a DC circuit with multiple resistors.

The first one looks like this:
12 V 4 ohms
|------:|:|-----\/\/\-----|
| |
| 18 V 12 ohms |
a|------:|:|----\/\/\------|b
| 8 ohms |
|-----------\/\/\---------|

I am trying to find the current through the 4 ohm resistor, but I am not quite sure how to go about doing so. I tried subtracting the voltages since they are in parallel and finding the equivalent resistance and then using Ohm's Law, but that was unsuccessful. I have a feeling it might intend for me to use Kirchoff's rules, so I then tried doing so from junction a to junction b. I got Vab=16-4I1=18-12I2=8(I1-I2 (I1 is from b to a around the top, where the 16 V and 4 ohm resistor is, I2 is from b to a directly across the middle, and I3 is from b to a along the bottom, where the 8 ohm resistor is), but just didn't know where to go from there. Would the current be I1, or something else?

The second problem is quite similar. In this one, I am trying to find the power given off my one of the 10 ohm resistors; I think my problem here is again the current, as power=I^2 * R.
It looks like this:
12 V
|-----:|:|-------------|
| |
| |
| 2 ohms |--\/\----| <----20 ohms
|---\/\------|---\/\---| <----10 ohms
|---\/\---| <----10 ohms
So basically I am trying to find the current through one of the 10 ohm resistors so I can use it to find power, which is I^2 * R.

I would really appreciate some help on this, as I am studying for a test, and these two problems have been troubling me for much too long.

Thanks!

Related Introductory Physics Homework Help News on Phys.org
Somehow those diagrams turned out horribly. I've attached some better ones; "Untitled" is corresponds to the first problem and "Untitled 2" corresponds to the second.

Thanks!

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