A Kirchhoff's Law Circuit Analysis Problem

[Ownaginatious]

Homework Statement

If R=1.29×103 Ω and ε=239 V, determine the magnitude of the current in the horizontal wire between a and e.

http://img10.imageshack.us/img10/3746/sbpic2823.png

Homework Equations

Kirchhoff's circuit laws.

The Attempt at a Solution

I'm having trouble mostly with getting this thing started. The problem I'm having is that I don't know how to properly figure out what the directions of the current throughout the circuit are.

I checked with a simulation program, and it tells me all the directions go like this:

http://img10.imageshack.us/img10/4135/sbpic.png

I don't understand how I'm supposed to predict that though...

I'm also having trouble establishing the voltage loops in the circuit. If the current is considered the way it is above, doesn't that mean that I can't use the exterior rectangular part of the circuit as one loop?

If someone could help guide me through this a little, or at least get me started on the right path, it would be very helpful. I'm normally pretty good at physics... but this circuit analysis thing is through me off a bit... maybe I just really suck at electricity :p.

Also, if anyone knows of any good resources (i.e. Youtube videos or other websites) for learning this stuff with guided examples, could you sent the link? The only videos I've been able to find so far are with ridiculously easy examples only containing one battery and a couple resistors.

Thanks!

 

[Kruum]

You don't need to predict the directions of the currents. You can determine the direction from the sign of your answer, if its negative the current is flowing to the opposite direction of what your arrow shows. And this question is quite easy, if you calculate the currents of both supplies separately. So change one of the voltage supplies to a short circuit and calculate the current between a and e. The do the same for the other supply and sum the two currents.

Btw: Nice username!

 

[nlightner]

I would suggest the following steps to solve this Kirchhoff's Law circuit analysis problem:

1. First, draw a clear and accurate diagram of the circuit, labeling all the components and their values.

2. Identify the nodes in the circuit, which are the points where current can flow in or out.

3. Apply Kirchhoff's Current Law (KCL) at each node, which states that the sum of the currents entering a node is equal to the sum of the currents leaving the node. This will help you determine the direction of the current in each branch of the circuit.

4. Apply Kirchhoff's Voltage Law (KVL) to each loop in the circuit, which states that the sum of the voltage drops around a closed loop is equal to the sum of the voltage rises. This will help you determine the magnitude and direction of the voltage drops across each component in the circuit.

5. Use Ohm's Law (V = IR) to calculate the voltage drops across the resistors and the current flowing through them.

6. Once you have determined the current in each branch of the circuit, you can use KCL again to calculate the current in the horizontal wire between a and e.

7. Finally, check your answer by using the simulation program provided or by solving the circuit using a different method.

As for resources, there are many online tutorials and videos available for learning Kirchhoff's Laws and circuit analysis. Some good examples can be found on Khan Academy, All About Circuits, and Physics Classroom. It may also be helpful to practice with simpler circuits before tackling more complex ones.