20.3 Electric Circuits
Reading Focus
Key Concepts
What is included in a circuit diagram?- How do series and parallel circuits differ?
- How do you calculate electric power and electrical energy use?
- What devices make electricity safe to use?
Vocabulary
electric circuit
series circuit
parallel circuit
electric power
fuse
circuit breaker
grounding
Reading Strategy
Relating Text and Visuals Copy the table below. As you read, look at Figure 13 on page 610. List three things that the diagram helps you understand about circuits.
| What Can Be Seen in the Circuit Diagram? |
|---|
Wire bringing current from outside a. b. c. |
If you've ever seen a house being built, you know that wires hidden inside the walls connect to every electrical outlet and to every light switch. If you were responsible for wiring a house, like the electrician in Figure 11, how would you do it? A good place to start would be the circuit diagrams supplied by the builder or contractor.
Circuit Diagrams
An electric circuit is a complete path through which charge can flow. Wires in a house form a complex network of circuits. It may look like a maze of wires, but each connection has a purpose. An electrician uses circuit diagrams to keep track of how elements in a circuit are connected. 
Circuit diagrams use symbols to represent parts of a circuit, including a source of electrical energy and devices that are run by the electrical energy. In a simple circuit, for example, a battery provides the energy to operate a device such as a bell or a light bulb.
A circuit diagram shows one or more complete paths in which charge can flow. Switches show places where the circuit can be opened. If a switch is open, the circuit is not a complete loop, and current stops. This is called an open circuit. When the switch is closed, the circuit is complete and charge can flow. This is called a closed circuit.
Figure 11 To bring electric current into a building, an electrician installs wiring. In a house, all of the wires usually come from one main box.
What is an open circuit?
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