Unit 1 Lesson 2

How does energy transfer through a circuit?

Building a Simple Circuit

All electric circuits have at least two parts: a power 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 to the right.

The power source of this simple circuit is a battery. In a home circuit, the source of power 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 to the right, the wires are connected to both terminals of the battery, so they form a closed loop.
Most circuits have electrically powered 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.

Building a Simple Electric Circuit

On the simulation to the right, click on "Intro"

Build a circuit with a switch that can turn on and off a light using as few materials as possible.

As you build your circuit, consider the following questions:

What materials (besides the switch and light bulb) were needed to build this circuit?
How many connections did you circuit have to your light bulb?
How many connections did you circuit have to your battery?

Building a Circuit with More than One Electrically Powered Device

On the simulation to the left, click on "Intro"

Task 1: A Series Circuit

Build a circuit with one switch and two light bulbs. The switch should be able to turn on and off both light bulbs.

As you build your circuit, consider the following questions:

How was this circuit similar to your simple circuit with one light?
What happens if you cut the connection to one light bulb in the circuit?

Task 2: A Parallel Circuit

Next, build a circuit with two switches and two light bulbs. Each switch should be able to turn on and off one light bulb.

As you build your circuit, consider the following questions:

How was this circuit different than the "Series Circuit"?
What happens if you cut the connection to one light bulb in the circuit?

Circuits with More than One Device

Series Circuit

Devices have lower output (less bright) compared to one device alone
If one device removed (light bulb burns out) the other device is not powered

Parallel Circuit

Devices have same output (same brightness) compared to one device alone
If one device removed (light bulb burns out) the other device remains powered

Power Loss in a Circuit

Broken Circuit

The circuit is not a complete loop. In other words, the path of conducting metal around the circuit is broken. The device will not be powered.

Short Circuit

A new loop, without a device, is introduced. Energy takes the new "shorter" path. The device will not be powered and the power source will overheat.

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