# electric circuits

## circuit diagrams

When a contractor builds a new home, she uses a set of plans called blueprints that show her how to build the house. The blueprints include circuit diagrams. The diagrams show how the wiring and other electrical components are to be installed in order to supply current to appliances, lights, and other electric devices. You can see an example of a very simple circuit in the Figure 1.2. Different parts of the circuit are represented by standard circuit symbols. An ammeter measures the flow of current through the circuit, and a voltmeter measures the voltage. A resistor is any device that converts some of the electricity to other forms of energy. For example, a resistor might be a light bulb or doorbell. A: The battery symbol (or a symbol for some other voltage source) must be included in every circuit. Without a source of voltage, there is no electric current.

## electric circuit basics

A closed loop through which current can flow is called an electric circuit. In homes in the U.S., most electric circuits have a voltage of 120 volts. The amount of current (amps) a circuit carries depends on the number and power of electrical devices connected to the circuit. Home circuits generally have a safe upper limit of about 20 or 30 amps.

## parts of an electric circuit

All electric circuits have at least two parts: a voltage source and a conductor. They may have other parts as well, such as light bulbs and switches, as in the simple circuit seen in the Figure 1.1. The voltage source of this simple circuit is a battery. In a home circuit, the source of voltage is an electric power plant, which may supply electric current to many homes and businesses in a community or even to many communities. The conductor in most circuits consists of one or more wires. The conductor must form a closed loop from the source of voltage and back again. In the Figure 1.1, the wires are connected to both terminals of the battery, so they form a closed loop. Most circuits have devices such as light bulbs that convert electrical energy to other forms of energy. In the case of a light bulb, electrical energy is converted to light and thermal energy. Many circuits have switches to control the flow of current. When the switch is turned on, the circuit is closed and current can flow through it. When the switch is turned off, the circuit is open and current cannot flow through it.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

electric current can flow through a circuit only when there is a source of voltage.

``````-->  a. true

b. false
``````

the amount of electric current a circuit carries depends on the

``````a) voltage of the circuit.

b) number of electrical devices connected to the circuit.

c) power of the electrical devices connected to the circuit.

-->  d) all of the above
``````

home electric circuits generally have a safe upper limit of 120 amps of current.

``````a. true

-->  b. false
``````

in most circuits, the conductors are

``````a) batteries.

b) switches.

-->  c) wires.

d) none of the above
``````

current will not flow through a circuit when the circuit is closed.

``````a. true

-->  b. false
``````

## diagram questions

No diagram questions associated with this lesson