# Physlet^{®} Physics 2E: Optics

## Chapter 30: DC Circuits

Direct current (DC) circuits are those circuits where the current does not vary in time (aside from when a switch opens or closes). They are characterized by batteries, bulbs, resistors, switches and, occasionally, circuits with capacitors. Using V = IR (Ohm's law) and conservation of energy and charge, you should be able to understand circuits made up of these components, figure out what a given circuit does, and design some simple circuits. Understanding DC circuits provides a beginning for understanding the electronic appliances and equipment around us.

## Chapter 31: AC Circuits

Alternating Current (AC) circuits are circuits where the current and the voltage vary sinusoidally in time (in comparison with DC circuits where the voltage and current are constant). AC is the type of current you get from wall outlets; the current switches direction 60 times a second (60 Hz current). With AC, we begin the study of circuits with non-linear circuit elements such as capacitors, inductors and transformers, which are the back-bone of analog and power electronics.