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# 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.

# Table of Contents

## Illustrations

- Illustration 30.1: Complete Circuits.
- Illustration 30.2: Circuits, Voltage, and Current.
- Illustration 30.3: Voltage and Current Dividers.
- Illustration 30.4: Batteries and Switches.
- Illustration 30.5: Ohm's "Law".
- Illustration 30.6: RC Circuit.
- Illustration 30.7: Loop Rule.

## Explorations

- Exploration 30.1: Circuit Analysis.
- Exploration 30.2: Lightbulbs.
- Exploration 30.3: Designing a Voltage Divider.
- Exploration 30.4: Galvanometers and Ammeters.
- Exploration 30.5: Voltmeters.
- Exploration 30.6: RC Time Constant.

## Problems

- Problem 30.1: Draw the schematic diagram.
- Problem 30.2: Switched light bulbs.
- Problem 30.3: Find resistance, battery voltage and power dissipated.
- Problem 30.4: Rank resistances.
- Problem 30.5: Identify the correct graph.
- Problem 30.6: Bad circuits.
- Problem 30.7: Wheatstone bridge.
- Problem 30.8: Find the internal resistance of voltmeter and ammeter.
- Problem 30.9: Find internal resistance of battery in a network.
- Problem 30.10: Find resistance from power graph.
- Problem 30.11: RC circuit: rank the resistance of the light bulbs.
- Problem 30.12: RC circuit: find the capacitance.
- Problem 30.13: RC circuit with capacitor networks.