Find the Total Current in a Single Loop Circuit

[Walley1]

Homework Statement

Find the current flowing through the circuit.
http://wildedge.zxq.net/IMG.jpg

Homework Equations

Amps=Total Voltage / Total Resistance

The Attempt at a Solution

(20 + 12 + 12 + 3) / (10 + 5 + 30 + 40 + 20 + 15)=0.39A

I'm almost certain that this is wrong. I don't even know if the formula I used is actually valid. Any help you can provide would be greatly appreciated.

On an unrelated note, has anyone seen a good explanation of the right-hand rule (for magnetic fields)?

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[gneill]

Your Relevant Equation is okay, but beware that the polarity of the individual voltage sources matter; look closely at each of the battery symbols as you 'go around' the loop.

 

[jianghan]

if you go around the loop carefully, i think the answer is (-20+12+12-3)/(5+30+40+20+15+10)=0.00833A