Circuits Lesson

Last updated on February 14, 2008

Electricity and Basic Circuits Lesson Plan Lesson Objectives 1. Be able to draw and explain how an electrical circuit works. 2. Be able to construct a simple circuit, a series circuit, and a parallel circuit. 3. Be able to define and use vocabulary associated with electricity and circuitry. Vocabulary: Circuits, electrons, series, parallel, resistor, etc. 4. Be able to explain how resistors work (if there is time). Lesson Materials •

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In paper bag for each student team of 3-4 students, and for the instructor, not connected together:
One 9V battery
One 9V battery clip that snaps into the top of the 9V battery and outputs to two wires
One small flashlight bulb
One light bulb holder
Four wires with alligator clips at each end In addition, to be included in the instructor’s bag: o Package of resistors for showing the effects of resistors on bulb brightness (if there is time). o A second light bulb and light bulb holder for each student team as well as for the instructor for use in experiment 2.

Introduction Lecture (10 minutes) Ask the students, “What do you think of when you think of ‘electricity’?” Make a list up front on the board of answers the students come up with as well as a list of items in the student’s homes that run on electricity. Then ask students questions like “Where does this electricity come from?” and “How do we get light and energy from it?” Introduce the term “circuit” and explain that today we are going to learn to build electric circuits, similar to the ones that make things work in our houses. Experiment 1: Simple Circuits and How they Work (25 minutes) We will hand out paper bags containing circuit parts, and have the kids explore the contents of the paper bag. Ask the students to try and make the light bulb light up and help the kids assemble the circuit in the ways they suggest. The tutors can ask some prompting questions (e.g. “What do you think this does?”) but should not guide the students in their circuit construction.

Last updated on February 14, 2008 Warning: Do not let the students touch the 9V batteries to their tongues, as people sometimes do to check that the battery is still charged. While this won’t hurt the students, it will cause them discomfort, and it will rapidly discharge the battery. Preferably, you should not mention to the students that they can touch the battery to their tongues (so as to not give them ideas), and should only take action to stop students from doing it if you see them doing it. Before the 10 minutes are up some students will have undoubtedly have made a simple circuit with the contents of the bag. At this time we stop for a brief discussion. Have the students explain what they did so others can follow. Now break briefly for a discussion on how the circuit works. We will explain with a water pipe metaphor: the battery is like a pump, the wires are pipes, the electricity is the water, and the light bulb powered by the water moving (like a paddle wheel). We can do this Q&A style as well: “What do you think are like the pipes? Pump? Water? Etc” Explain to the students that in our homes there are electric outlets that are very large sources of electric power- so large that it can be dangerous, even deadly for us to touch electric outlets. After the brief discussion, have the kids draw a diagram of the circuit on their handout. The students should make arrows describing the path the electrons take (battery to light bulb and back to battery). Experiment 2: Series and Parallel Circuits (20 minutes) Once we’ve drawn our circuits, we distribute a second light bulb with a holder to each group, and it is the kids’ job to build a circuit where both bulbs are lit. There are TWO solutions to this (series and parallel). Give the kids ~5 minutes to see if they can come up with an answer on their own. Then the tutors should prompt solutions. Once the group has come up with one solution, the tutor should ask, “Can we think of another way to get both bulbs to light up?” The tutor and the kids should then try to assemble the second type of circuit. With the older kids, the tutors can provide the names of the two types of circuits. After both types of circuits have been assembled, the kids should draw diagrams of both circuits, and answer the following questions on the handout. The circuit diagrams should include arrows again to describe the paths the electricity takes. This will be very helpful in understanding questions 2-4. The tutors should then ask the students the following questions as a class and have students answer: 1. Which circuit makes the light bulbs brigher? Why do you think that is? Use the water in pipes metaphor to help answer this question. 2. Unscrew a light bulb in the series circuit. What happens to the other one? Why? 3. Unscrew a light bulb in the parallel circuit. What happens to the other one? Why?

Last updated on February 14, 2008 4. Based on these observations, what kind of circuit do you think you have in your house? Why? Experiment 3: Resistors (Time permitting, remaining time) Go back to the pipe metaphor. Ask the kids what would happen if there were rocks in the pipes, in terms of the circuit? Sample answers: less water flowing, light bulb not as bright, etc. Explain that we can put “rocks” in the circuit with something called a resistor. Prepare the tutor demonstration to illustrate the effect of resistors in series on the circuit and in particular on the brightness of the bulb. • Demonstrate the effect of the smallest resistor (likely 1 kilo-ohm) on the circuit and have the students observe the light. • Demonstrate the effect of the middle size resistor (likely 10 kilo-ohm). What happens to the light? • Demonstrate the effect of the largest resistor (likely 100 kilo-ohm). Now what happens? Throughout the tutor demonstration, have the kids write down their observations on the handout. Try to get them to understand resistors in terms of “rocks in the pipe.” What is meant by a “larger resistor?” Why is the brightness go down when the resistance goes up? Recap (5 minutes) Back in the main group, with a simple circuit diagram on the board. Ask the students what each element does (battery, wires, light bulb). Draw up a series and parallel circuit on the board and have the student identify these circuits by name, emphasizing the use of electrical vocabulary. If classes get to it, ask the students to explain how the resistors work, in terms of the rocks in the pipe metaphor. Scientific Background Explanation for Tutors Sometimes trying to understand a complicated new idea can be easier if we compare it to something we are already familiar with. This is called making an analogy. For example, understanding electricity in circuits can be easier if we compare it to water flowing through pipes. Think of the battery as a kind of water pump, and wires as the pipes through which the pumped water flows. In order for the pump to keep pumping, it must have some water to pump – therefore, the water pipes must come out of one side of the pump and eventually return to the other side. Along the way, the water pipes can pass through many different devices – the two we will play with today are called light bulbs and resistors.

Last updated on February 14, 2008 A light bulb converts electricity into light. Think of it as a device which creates light as water passes through it – the faster water passes through, the brighter the light. A resistor limits how much electricity can flow in a circuit. Think of it as a pipe which is blocked by a pile of rocks – the more rocks there are, the harder it is for water to flow, which is what we call a high resistance. We are looking at two different ways of connecting a battery with two lights bulbs. One way is called a series connection – here a wire connects one side of the battery to one side of the first bulb, and another wire connects the other side of the bulb to the second bulb. The other side of this second bulb is connected to the other side of the battery. If we think about this as water pipes, water flows from the pump (battery) through two bulbs, one after the other – this is why we call this a series circuit. Another way of connecting two bulbs to a battery is called a parallel connection. Here two wires lead from one side of the battery and connect to two different bulbs. The other sides of these bulbs connect back to the other side of the battery. If we think about this as water pipes, water flows in two loops from the pump through one bulb and then back to the pump.