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.