- Iii Using Kirchoff S Rules To Solve Circuit Problems A Label The Current And The Current Direction In Each Branch Not 1 (44.07 KiB) Viewed 38 times
III. Using Kirchoff's rules to solve circuit problems A. Label the current and the current direction in each branch. Note that in many cases it's hard to tell which the correct direction for the current is in a particular loop. That does NOT matter. Just make an educated guess. If you guess wrong, you'll get a negative value for that current, which is fine. The value is correct and the negative sign indicates that the direction is opposite to the way you drew it. However, always remember to use the negative sign in your calculations of other values. B. Mark the ends of the battery with +/- and use the direction of the currents you selected to label the ends of each resistor with +/- to indicate which end is at a higher/lower electric potential. C. Use Kirchoffs junction rule to write equations for each junction. Note that usually, writing down equations for half the junctions is sufficient since the other junctions will give you equivalent equations. D. Use Kirchoff's loop rule to write down loop equations for all the loops in the circuit. i. Top loop ii. Outer loop 111. Bottom loop We now have to solve for the unknown currents. To do this, we will ALWAYS use at least one junction equation and one loop equation. E. Write down the three equations you will need to use to solve for the three unknown currents. Pick the easier two of the three loop equations. General strategy to solve for the three currents: • You now have three equations, two loop equations which include only two currents, and one junction equation which includes all three. Identify the current that is common in the loop equations. Use those equations to solve for the other currents in terms of the common one. For example, if the common current is Is, use the two loop equations to solve for I and I, in terms of Is. Plug in the junction equation.
Tutorial: Analyzing Circuits F. Use the general strategy outlined on the previous page to solve for the three currents. 40.00 20.00 40.0 22 AAA IV. Practice A. For the circuit on the right, pick a direction for the current in each branch. B. Label the ends of batteries and resistors with +/- to indicate which end 15 at a higher lower electric potential C. Write down Kirchoffs junction rule for half of the junctions (here, there are two junctions and they give you the same equation). 70.00 50.092 20.02 120 V D. Write down Kirchoff's loop rule for as many loops as you need to solve for all the unknowns. E. Use the general strategy outlined on the previous page to solve for the currents.