Solving Kirchoff's Law Questions: Finding Current Direction

[gmx]

kirchoff's law??

Hi

Sometimes in kirchhoffs law questions it gives the circuit without showing the direction of the current so how do I determine the direction of the current (not the direction that I choose to solve the question)?

please help!
I have exam tomorrow

 

[jtbell]

If you don't know the direction of the current in a certain section of the circuit, simply make a guess, and set up your equations accordingly. If you guessed the wrong direction, the current in that section will come out negative, but the magnitude will still be OK, so remove the minus sign and flip the current-direction arrow around on your diagram.

 

[gmx]

thank you very much
I have another question if you don't mind
how do I know from where does I1 start and end? also for I2 and I3

 

[jtbell]

Generally, the different currents start and end at junction points. You should always start out by assuming different currents between different junction points, or along different paths between the same two junction points.

 

[DrummingAtom]

My circuits professor always assumes that all current is going away from each node; so the sum of all the currents at a node equal 0. I personally haven't adopted this method because I find it confusing but and professor and some of my friends live by it. Here's a link that explains this method. The good thing about is you don't have to worry about signs until the end.

http://www.mathonweb.com/help/backgd5.htm

 

[adam2000]

the different currents start and end at junction points.http://www.hergoods.info/avatar1.jpg