# Chapter 13: Electric Circuits: Batteries and Resistors

**At Grade**Created by: CK-12

## Introduction

### The Big Ideas

The name *electric current* is given to the phenomenon that occurs when an electric field moves down a wire at close to the speed of light. *Voltage* is the electrical energy density (energy divided by charge) and differences in this density (voltage) cause electric current. *Resistance* is the amount a device in the wire resists the flow of current by converting electrical energy into other forms of energy. A device, the resistor, could be a light bulb, transferring electrical energy into heat and light or an electric motor that converts electric energy into mechanical energy. The difference in energy density across a resistor or other electrical device is called *voltage drop.*

In electric *circuits* (closed loops of wire with resistors and constant voltage sources) energy must be conserved. It follows that changes in energy density, the algebraic sum of voltage drops and voltage sources, around any closed loop will equal zero.

In an electric *junction* there is more than one possible path for current to flow. For charge to be conserved at a junction the current into the junction must equal the current out of the junction.

- 13.1.
## Voltage and Current

- 13.2.
## Ohm's Law

- 13.3.
## Resistors in Series

- 13.4.
## Resistors in Parallel

- 13.5.
## Resistor Circuits

- 13.6.
## Energy Efficiency

- 13.7.
## Internal Resistance

### Chapter Summary

## Summary

In these lessons students will gain a strong conceptual footing of electricity. In addition, they will learn how to solve circuit problems containing resistors wired in all different ways. Power, efficiency and internal resistance are also explored and students learn to solve problems involving these concepts as well.

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