# How do I decide whether to use Kirchhoff's Voltage Law or Kirchhoff's Current Law?

When I solve questions, I usually get confused between when to use the Kirchhoff's Voltage Law (KVL) and when Kirchhoff's Current Law (KCL). Please help.

• I don't even use these. :/ I just break everything down into voltage dividers. – endolith Nov 2 '10 at 4:08
• And I dont even know voltage dividers properly.. – user1799 Nov 2 '10 at 20:16
• What are KVL and KCL? Definitions please. – Connor Wolf Apr 28 '11 at 6:09

## 3 Answers

Whichever gives an easy set of equations. If you are doing resistor networks, count if there are more loops or more nodes. KVL if there are more loops, KCL if there are more nodes.

In more advanced circuits, like transistors, there is normally a very specific mode that lends itself to your problem space.

• True. I sometimes find myself trying both, just to find out wich will yield the more convienent set of equations. – zebonaut Nov 2 '10 at 8:45

Do you want to solve for currents first, or voltages? Certainly once you have all the currents you can work out the voltages, and vice versa, but sometimes you're really after one or the other.

If you apply KVL, you end up getting currents first. This is because, to write the voltage drops around the loops, you use ohms law with the loop current, which is your unknown. So you write a system of loop equations and the solution gives you currents.

Conversely, with KCL, you can write the expressions for current into a node using ohms law to find the current contribution of a component in terms of the voltage differences between the node in question and the other node the component is attached to. Solve this system and you arrive at voltages.

• So to find 'V' kcl and to find 'I' Kvl that whats used often? – user1799 Nov 2 '10 at 11:43
• I have taught that a million times, but somehow I forgot it in my post. You always solve for the opposite of what your intuition tells you. +1 to justjeff, spot on reason to choose one. – Kortuk Nov 2 '10 at 15:33

It depend of how many nodes/meshes your circuita has. However, you can use online calculator for any linear 2X2 system:

http://www.cirvirlab.com/simulation/kirch_2_real.php