Chapter 11 Lesson 5, "Series Circuits"
Materials:
Objective:
Anticipatory Set:* Show the students a picture of Christmas lights. Ask what would happen if one of these bulbs burned out. How do you know. Not all lights are set up like this some lights are set up so that if one goes out the electricity can flow around that bulb.
Teacher Input:* When there is only one path for electricity to flow it is called a series circuit. A switch works well on a series circuit because if you open it the electrons have no way to get from the negative side of the battery to the positive side. So, all the lights go out. Look at the following pictures and try to determine if the circuit is a series circuit. Circuit 1, Circuit 2, Circuit 3, Circuit 4, Circuit 5. It is not always an advantage to have things in series. Here you see that if two bulbs are both on the same series circuit they have to share the available voltage that makes them half as bright. The more bulbs you add the less bright they are. In the third one would the bulbs both have all the available voltage of the battery or would they have to share it. Next have the students answer this question. Ask what would happen if bulb B goes out. What would happen if bulb A goes out? Well, that is what happens when bulbs are in series with one batteries. What happens if more than one battery is hooked up in a series?
When batteries are hooked up in series there electromotive force is multiplied by the number of batteries. Here you have 4 1.5 Volt batteries. When they are in series the electromotive force or voltage goes up to 6 volts. Here we have two 6 volt batteries hooked up to a single circuit. Are they hooked up in series? What is the total voltage? In this last picture of batteries use what you know about the little square batteries and determine how much voltage is available for the light. Notice that the batteries are connected in series because each + is connected to the next ones -.
Demonstrate what happens when you take just one of those 9 volt batteries and touch it to steel wool. The steal conducts the electricity and heats up causing it to oxidize and burn up. When the current within a conductor increases it heats up. Show this mass of melted wire. this wire has had too much current put though it causing it to melt. Here you see all kinds of outlets and switches that have melted because too much current has been sent through it. What do electricians do to make sure that too much electricity is not flowing though a circuit causing a fire? There are a few things they can do. First this is a common thing you see in your electrical systems in your snow machines and cars. The small wire in this is designed to burn up before the wire does. As long as it is in a series circuit the electricity will stop flowing when this happens. This may be a familiar electrical tool that you use. It is called a surge protector and if the current in the circuit goes up too high it breaks the circuit which protects anything plugged in from being damaged by too much electricity. In you homes you also probably have something that looks like this. This is designed to limit the amount of electricity flowing through the wires in your home. If you have too much you could burn your house down if the wires catch on fire. Here is how it works.
Guided Practice:* Students will work in pairs or small groups to answer the questions on Page 332.
Independent Practice:* Students will read Lesson 5 and complete the worksheet, 11-05 "Series Circuits"
Check for Understanding:* Students will take the quiz online, 11-05 "Series Circuits"
Duration:
30 minutes + 10-15 for Independent Practice (Could be longer if taken for homework).
Alaska Content Standards Addressed in this lesson:
