Lesson 2: Wiring the House for LED Lights (1 Day)

Lesson 2: Wiring the house for LED lights (1 day)

In this lesson students will review circuits, electron flow, current and voltage. This topic is part of the 6th grade science curriculum. Discuss and come to a consensus regarding using parallel or series circuits when wiring the house. (*connect with real world by talking about how houses are wired, breaker boxes, overloads, etc. Will connect with power grid when looking at transmission system and how it is designed to handle surges, etc.) Wire and put in 2-4 LED lights. (Make sure students put some tape on the wire attached to the + LED terminal.) You could also have students make street lamps to go with their house. Materials: circuit board and/or phet simulation about DC circuits (will need a computer with internet connection and projector if using the phet simulation), wire, LED lights, masking tape, multimeter (to test LED lights to make sure they work), two 1.5 volt batteries

Introduction: Place the circuit board at the front of the classroom so all students can see it. Explain that it is a circuit board and that today they will have a chance to remember content their learned during their 6th grade science class about series and parallel circuits. Show the students how the metal pieces can move and ask them which arrangement would be open or closed to allow electricity to flow through the device. (The metal pieces must be secured on both ends to the posts to be closed and for electricity to flow.) Ask students what electricity is. Students should be able to explain that it is the movement of electrons from one place to another as this was part of the 6th grade curriculum. Instruct students to have out a piece of notebook paper. Tell them that you are going to change the position of the metal connectors and then run a current through the system. Instruct them that they are to draw the system on their paper including where you are going to attach the connectors for the current. They will then write their prediction of what they think will happen once the current is connected. Once everybody has written his or her prediction, connect the current to the system. Tell students to mark on their diagram what happened (which lights lit up). Do this for the following arrangements, giving students time to record their observations on their paper. Students may ask you to redo a specific circuit arrangement so they can see it to refresh their memory or you may want to show them a circuit again to help them see the differences between parallel and series circuits. Circuit Board Arrangements:

1. single light 2. 2 lights in series

3. 3 lights in series

4. 4 lights in series

5. single light again 6. 2 lights in parallel

7. 3 lights in parallel 8. 4 lights in parallel

At this time ask students to reflect on their observations and ask them which circuit arrangement, parallel or series resulted the brightest bulbs.

Background knowledge you will need to help students: Remind students that electricity is flowing through the circuits when it is closed and that the electricity flows in one direction, from the - to the +. Point out that batteries have two ends, a positive and a negative terminal and plugs have at least two ends. When batteries are part of the circuit the electricity flows from the negative terminal through the circuit and returns to the battery through the positive terminal to complete the circuit. If you are using an outlet, electricity will flow from the wires in the wall into the first prong, through the wires and body of whatever the object is and back into the wall through the second prong. If the plug has a third prong this is used for grounding or helping to reduce the chances of experiencing an electrical shock from the appliance.

Go back to the circuit board and set it up for two lights in series. Ask students to identify how many different options for a pathway the electricity can flow through the system. If the first bulb blows will the second one still light up? Why or why not? Unscrew the first light to simulate a blown bulb and see what happens. Draw a diagram of a light bulb on the board and guide students to the realization that the electrons are flowing through the filament of the light bulb and that when the filament of the first one is gone this breaks the circuit and the electrons cannot continue to flow through the system. Set the board up for two lights in parallel and have the students identify the pathways the electrons flow the first and the second light. Ask students what will happen to the second bulb if the first bulb were to blow or be removed. Would the second light still be lit when the current flows through the system? Why or why not? Show the students what happens. Have a student come to the board and explain on the diagram what is happening. Application:

Once students understand what is happening in parallel and series circuits, ask them which type of circuit they think would be the best one to use in house and why. (Students should eventually come to the conclusion that parallel circuits are the best choice. If houses were wired in series circuits if something broke or became disconnected then everything else down the series would not work. In parallel, even if something becomes disconnected or breaks, current can still flow to the other items and they will still work.)

Instruct student that they need to work together to decide where they are going to place 2-4 LED lights in their house. Make sure they know that the lights must be visible from the outside of the house. Once they know where the lights are going to go they will need to wire the lights and the house. They will test their circuit using two 1.5 volt batteries in series. Make sure to inform students which end of the LED is the positive terminal and which end is the negative. As students are working on the challenge circulate through the groups as part of the formative assessment. If a group’s lights do not work, use a multimeter to make sure they work and then use questions to help guide the students to possible solutions for their problem. Ask them if they should use a parallel or series circuit. They should say parallel. Ask them to explain how things should be connected for the lights to be in parallel. Have them draw it out on their paper to help them visualize how things should be connected. Then have the students talk through their plan for where the lights are going to go and how to run the wire inside the house. Remind students that they also need to think about where the wires will come out of the house so they can connect to the different sources of electricity that will be used.

Assessment: The finished product of the lights inside their house working.

Resources about circuits http://electronics.howstuffworks.com/everyday-tech/question110.htm http://www.bbc.co.uk/bitesize/ks3/science/energy_electricity_forces/electric_current_voltage/r evision/4/ http://www.education.com/science-fair/article/parallel/ http://www.jimsdestinations.com/elebas3.htm http://science.howstuffworks.com/environmental/energy/circuit2.htm List of several videos about circuits: http://www.watchknowlearn.org/Category.aspx?CategoryID=1764