• Students will complete an online performance assessment by building and completing a simple circuit and a parallel circuit successfully. The Web site Make an Electric Circuit Online at http://gwydir.demon.co.uk/jo/elect/index.htm provides instructions.

Students will be introduced to the concept of electricity by watching a short video with a catchy tune that will have them looking for similar examples of electricity right in the classroom. Extend this activity to walking through the school and noting all the uses of electricity. For homework, ask students to make a list when they go home. Several fun activities engage students to consider what is meant by an electric circuit and how electrons flow through wire as either open or closed circuits. Then students will have the opportunity to explore how a flashlight works by taking it apart and drawing the components and then lighting the bulb and putting it back together. Through this activity, students will experiment with lighting bulbs and learn the difference between simple series and parallel circuits.

Part 1: What Is Electricity and What Is Meant by Open and Closed Circuits?

Review what students know about electricity as a form of energy from previous lessons (i.e., Where do we get it from? Is it kinetic energy? It is potential, or stored, energy like batteries? How do we use it?).

Turn on various electrical devices in the classroom (CD player, light, TV, etc.) Ask students to give other examples of electricity they see in the classroom or in their homes and how the devices are able to work. Once students give “energy” as the answer, ask them to define it. Energy is defined as the ability to do work or make a change.

If time allows, take a walk through the school and write down all the appliances, devices, machines, etc. that use electricity.

Have students stand in a circle, close enough to pass items from one student to the next but far enough apart that just their hands touch. Give each student a ball (e.g., a tennis ball). Explain to students that they have to pass the balls from one person to the next with each person only holding one ball at a time. Give students time to complete the task.

Remove one student from the circle and ask students to pass the balls as before. They should not be able to complete the task due to the open space. Collect balls and have students remain in the circle.

Ask students to use different words to describe the two different scenarios. Make a list on the board and be sure that “open” and “closed” appear on the list.

Now tell students they are going to pretend their arms are the wires that carry electricity. Have them touch palms to complete the circle.

Ask two students next to each other to stop touching each other and ask students if the current is open or closed. Now have the two students each hold one end of a metal strip. Now ask if the current is open or closed.

Explain that the metal strip is a conductor and as long as each student is touching the metal “switch,” electricity can flow. If the switch is turned off, by one student letting go of the metal strip, the current will stop or is open so that electricity cannot continue to flow.

Wrap up the activity by explaining open and closed circuits and emphasizing two things that are needed: a power source and a complete circuit. Explain to students that wires in a circuit that connect objects (like switches, light bulbs, buzzers, etc.) must start and end at the power source before they can work. That’s why batteries have a top and bottom (+ and −) so they can carry the charge all the way around.

Part 2: How Do I Light a Bulb?

Before starting this activity, ask students what they would purchase if they were asked to go to the store and buy a pound of electricity. Ask them to think for a minute and then share their answer with their partner. Then ask for volunteers to write their answer on the board. If they answer “light bulbs,” ask if that means light bulbs are electricity. Or is it to say that light bulbs work using electricity? This is a good opportunity to correct misconceptions about electricity and reinforce the concept that electricity is not matter. You cannot hold it in your hand because it is a form of energy and does not have mass or volume like matter.

Break students into pairs and give them a flashlight. Ask if any of them have ever opened a flashlight before. Ask students to take the flashlights apart and take the inside parts out (spring, battery, bulb). Caution them about the breakable parts and to hold the flashlights over their desks in case these parts fall out. Have students draw and label the parts of the flashlight in their journals.

Without giving directions, ask students to light the bulb with only the parts that they removed from the battery casing. To ensure success and lessen frustration, the teacher can strip the ends of the wire with a wire stripper. Provide assistance as needed. Ask students why they think removing the plastic coating from the wire is important to solving the problem of lighting the bulb. Ask students to experiment and raise their hands once they light the flashlight. Instruct students to keep secret for the moment how they were able to light the flashlight. Instead have students draw a picture of what they did in their science journals while the other students complete the task.

Allow students to visit with other groups and try several ways to get the bulb to light. Ask students to draw ways that work and ways that do not work. Now ask students to use both batteries and the wire to light the bulb. It may be tricky but they will notice the bulb is much brighter now. Have students reassemble the flashlights and turn them on. Compare the brightness of the bulb now with the brightness when they lit the bulb outside the flashlight with the same two batteries. They should find them to be identical. Ask students to write in their journal what they have discovered, or any rules they established about getting a bulb to light.

Discuss as a class how to light a bulb and explain why it must be a closed circuit. Explain when you flip on a light switch, you are actually closing or completing the circuit. A circuit is the path that electricity flows. When you flip the light switch off, you are opening the current and the light turns off because the electrons cannot flow.

Ask students to show their drawings of their completed circuit. Are they alike or different? To simplify drawing circuits, there are common symbols to illustrate each part. Show students the symbols for drawing circuits. Hand out the Electrical Symbols Chart (S-4-5-3_Electrical Symbols Chart.doc) to each student. Using the symbols for batteries, wire, and a bulb, draw a simple circuit based on what students just did to light the bulb.

Now pass out switches and bulb holders to each pair of students and have them light the bulb using the switch. Take a moment and compare these materials to the ones they used to light the bulb in the flashlight. Now draw the simple circuit using these two new symbols. Ask a student to draw it on the board or overhead projector. Have students check their work.

Wrap up the activity for the day by reviewing what is necessary for a light to work in a house or classroom. Ask students to think about if and how the simple circuits can handle more than one light at the same time.

Part 3: What is a Simple and a Parallel Circuit?

Review the activity from Part 2. Discuss with students what one must have to light a bulb and a simple circuit. Ask them how many bulbs they were able to light in the previous activity. Now challenge them to see how many bulbs they can get to light using their knowledge of circuits from the previous activity.. Have students draw their setup once they light as many bulbs as they can. Who could light the most bulbs at one time on the same circuit? After applauding their efforts, ask them to draw the setup and label the parts using the new symbols. Ask students how they should label the pathways connecting the batteries, wires, and bulbs. When they say “circuit,” write it on the board and define it as a complete pathway from one end of the battery through the wire and bulbs to the other end of the battery and through the battery again. “This is that continuous pathway for the tiny charged particles called electrons that flow through the wire and carry the electric current.” Sketch together the circuit students constructed and label the parts. Students should have the same in their journals.

Example of a sketch with information:

The battery pushes electrons from the negative terminal (where there are many electrons), through the switch, the light bulb, and the wire into the positive terminal (where there are not many electrons). As electrons pass through the wire and into the light bulb, a special kind of wire inside the bulb, called a filament, lights the bulb.

The circuit has been broken. The light bulb is not lit. The flow of electrons has stopped because there is a gap in the circuit, and the electrons no longer have a closed path.

Discuss as a class how many bulbs were lit on one circuit. What did students notice about the light bulbs? (The more you add, the less bright they become.) “Why is this?” (Each bulb draws on the energy source and they become dimmer and weaker.) “There are two basic ways in which to connect more than two objects that use electricity: series and parallel.”

A series circuit has only one path for electrons to flow. Components are end to end in a line forming a single path. Ask students if they have put lights on a tree, and when they plugged in the lights, the lights didn’t work. If one bulb goes out, they all go out. This is one of the disadvantages of series circuits.

A parallel circuit may have multiple light bulbs because it has more than one continuous path for electrons to flow. Each individual path is called a branch. All components in parallel circuits connect between the same set of electronically common parts, or in other words they are connected across each other’s loads.

Have students work in pairs and try to build a parallel circuit. How many paths and bulbs can they wire with one battery? Have students draw their parallel circuits and demonstrate them to the class. Discuss the results and use the Series and Parallel Circuits handout (S-4-5-3_ Series and Parallel Circuits.doc) as a reference.

Series Circuits

A series circuit allows electrons to follow only one path. All of the electricity follows path #1. The loads in a series circuit must share the available voltage. In other words, each load in a series circuit will use up some portion of the voltage, leaving less for the next load in the circuit. This means that the light, heat, or sound given off by the device will be reduced.

Parallel Circuits

In parallel circuits, the electric current can follow more than one path to return to the source, so it splits up among all the available paths. In the diagram, some current follows path #1, while the remainder splits off from #1 and follows path #2. Across all the paths in a parallel circuit the voltage is the same, so each device will produce its full output.

Extension:

• Have students divide into three groups to debate the advantages and disadvantages of parallel versus series circuits. Group 1 (series circuits) and Group 2 (parallel circuits) will take turns arguing their side to a panel of objective students (Group 3). The third group will decide on a winner and explain why each group was given first or second place. Group 3 must relate their decision to the information learned throughout the lesson.