mrlovescience

It seems that students often have difficulty with these circuit problems where you have to solve for the voltage and current in each of the branches of a compound circuit.  Solving these types of problems is almost like completing a sudoku puzzle.  The first thing you need to do is solve for anything possible, even if it doesn’t initially seem to be going in the direction of your answer.  Often times, this is simply solving for the equivalent resistance of the circuit.  Once you have the equivalent resistance, you then use that information to solve for the total current in the circuit.

From there, you have to take a look at the schematic and problem to find out where to go next.  If there is a branch that is in a parallel arrangement with the batter, you can use ohms law to find the current in that branch.  If you have a resistor that is in series with the battery, you know that the total current is the current flowing through this resistor.  If you know the current and the value of the resistor, you can easily solve for the voltage drop across the resistor.

As you move around the circuit counterclockwise, you encounter two resistors that are in parallel.  Because you solved for the voltage drop for the one resistor in series, and you know the total voltage of the circuit, you can find the voltage drop in the parallel part by simply taking the difference.  Once you have the voltage across each of these resistors (same for both because they are parallel), you can find the current in each of the resistors using ohms law.

Again, the best advice is to look at what is given, and solve for some part of the circuit using this information.  Each time you use ohms law, you uncover another piece of information that will help you solve another part of the whole circuit.  I find that keeping all of the information in a table makes it much easier to keep track of the things you have solved for as well as the things you are still trying to figure out.