Rtot = Σi Ri

(1/Rtot) = Σi (1/Ri)

Gustav Kirchhoff (1824 - 1887)

Rule 1: The currents entering any junction equal the currents leaving that junction. (Conservation of charge!)

Rule 2: Around any loop, the potential rises equal the potential drops.  (Conservation of energy!)

Typical Example for Application of Kirchhoff Rules...

A collection of successively more elaborate worked examples.

Charging, q(t) = Q[1 - e(-t/RC)]; Discharging, q(t) = Qe(-t/RC).

Simple RC circuit!


1-10 Milliamperes--- Person will feel little or no electrical shock effects or sensation.

10-20 Milliamperes--- Painful shock will occur like a jolt, but muscle control will not be lost at this amperage.

20-75 Milliamperes--- This shock is more serious. You'll receive a a painful jolt and muscle control will be lost resulting in the inability to let go of something you may have grabbed that is shocking you.

75-100 Milliamperes--- As the current approaches 100 milliamperes, ventricular fibrillation of the heart occurs and damage is done.

100-200 Milliamperes--- Ventricular fibrillation occurs and death can occur if medical attention is not administered quickly.

Over 200 Milliamperes--- Severe burns and severe muscle contractions occur. Your heart can stop during a shock because the chest muscles put pressure on the heart. Internal organs can be damaged at this stage and if you survive, a painful recovery can be expected. What may surprise you about this level of shock is that through this clamping effect on the heart, ventricular fibrillation is avoided and the chances of a person's survival are good if the victim is promptly removed from the electrical circuit.

Current or Voltage?