**I welcome your questions and comments**.**-Charles Kim**. Email to me at ckimson@gmail.com

**The Laws of Circuit**** - **you can learn and practice by just
reading

Copyright. Charles Kim 2006

- How to become a
**circuit lawyer**? - To become a lawyer, study on law and
passing a bar exam would be necessary, in addition to the
actual practice. In the circuit theory, we have only 3
laws: Ohm's law (OHM), Kirchhoff's current law (KCL), and
Kirchhoff's voltage law (KVL). Of course, knowing the 3
laws does not make us good circuit problem solvers: we
need to practice the laws. Let's go over OHM: V=IR. OHM
seems too trivial to consider formally. A high school
science course seemed more than enough, and redundantly,
the second part of the physics again covers the OHM. And
the bad news is students still are not competent in
applying OHM in circuit problem. One thing we have to
remember in OHM application is (i) OHM applies to a
passive element, i.e., resistor; (ii) the voltage V in
the OHM equation is the voltage
*across*the resistor (not any other voltage in the circuit), and (iii) the current I is the current flowing*through*the resistor. My experience tells me that students do not have any problem with (i) and (iii) above. However, there are enough mistakes and problems involving with (ii). Remember that the V in OHM is the voltage across the element in which you apply the law. Don't assume that you can find V across or I though an element by a simple observation of a circuit. It may involve writing an equation of two with 1 or 2 variables. If you do not know the voltage across, then define it as, for example, Vx, and solve for Vx first applying KCL/KVL to other parts of the circuit. Then find, for example, I of the circuit.

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