DC Circuits 2 Overview

We are going to look in detail at what happens in circuits with capacitors and resistors together. We will need to use the Kirchoff Rules to investigate these circuits. In any circuit, the principles of conservation of charge and conservation of energy play a key role and form the basis of our analysis. We will see how these principles lead to Kirchoff's rules.

Conservation of Charge

The idea of conservation of charge is pretty simple. All branches of a circuit connect at junctions. Conserving charge means that the sum of the current flowing into the junction must balance the sum of the currents flowing out of the junction. Watch the charges in the animation below:

Particles coming from one branch flow into the other two branches, so that

I(in) = I(out 1) + I(out 2)

Conservation of Energy

If the electric field is conservative, then the sum of the potential drops around a closed loop must be zero.


These two principles form Kirchoff's rules.

Application of Kirchoff's rules

Keep these in mind as we do the exercises today.


Go to Exercise 1.