Unit Name: How things in your house work

Title: Electricity, Part 2: Circuits

Lesson Objective:

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.

Vocabulary: circuits, electrons, force, resistor

4. Be able to explain how resistors work.

Planners: Todd Anderson and Leslie Meltzer

Target age group: 2nd -5th grade

  • Materials
  • In paper bag, not connected together:
  • 1 battery holder
  • 1 AA battery
  • 1 small flashlight bulb
  • 1 light bulb holder
  • 4 wires with alligator clips at each end
  • Electronic playground kit
  • Set up for showing the effects of resistors on bulb brightness.

Intro Lecture

Ask, “What did we learn about last week?” Kids should remember lesson on static electricity, charge, etc.

Say, “What else do you think of when you think of ‘electricity’”? Make a list up front of things in their house that run on electricity.

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.

Part 1: Simple Circuits and How they Work

We will hand out paper bags containing circuit parts, and have the kids explore the contents of the paper bag. A tutor should be present in each group, but their role should be limited to helping the kids assemble the circuit in the ways the kids suggest. They can ask some prompting questions (what do you think this does?) but no more.

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. We can instead play with small sources of electricity, like 1.5 volt AA batteries.

After the brief discussion, have the kids draw a diagram of the circuit on their ditto. All ages should make arrows describing the path the electrons take (battery to light bulb and back to battery).

Part II: Series and Parallel Circuits

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 teacher 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 worksheet. The circuit diagrams should include arrows again to describe the paths the electricity takes. This will be very helpful in understanding questions 2-4.

  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?
  4. Based on these observations, what kind of circuit do you think you have in your house? Why?

Part III: Resistors (If time allows)

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.

Distribute the Electronic Playground. It’s prewired for one LED to light up when a loose wire is connected to one of three resistors of different strengths (1, 10, or 100 kilo-ohms).

--Touch the free wire to the smallest resistor (1 kilo-ohm). Observe the light.

--Touch the free wire to the middle size resistor (10 kilo-ohm). What happens to the light?]

--Touch the free wire to the large resistor (100 kilo-ohm). Now what happens?

Have the kids write down their observations on the ditto. 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?

If there’s extra time, feel free to explore the Electronic Playground with your group. There is a booklet attached with different wiring configurations. You can build more series and parallel circuits, or you can try for things more complicated, such as the sound system.

Recap

Back in the main group, with a simple circuit diagram on the board. Ask the kids what each element does (battery, wires, light bulb).

Ask the kids what kind of circuit they think they have in their house, and why.

Ask someone to explain how the resistors work, in terms of the rocks in the pipe metaphor.

Questions??

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Explanation

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.

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.