Generating Interest in Generators

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Objective

Students research how electric power is produced on a large scale and what natural resources we use as a country to to produce that power.

Big Idea

A changing magnetic field is required to induce an electric current in a coil of wire.

Context and Supplies

In the last lesson, Electromagnetic Induction, students learned that moving charge creates a magnetic field. This idea is foundational to the understanding of electric generators. Today, students figure out that the reverse happens as well: a changing magnetic field creates a current (moving charge) in a conductor. 

Students figure this out with another PhET simulation (PhET provides a series of high quality physical science simulators and is provided by The University of Colorado). Students use the Generator simulation to "discover" that only when the magnetic field is changing does a current move through a coil of wire. Students learn about this in the context of our electricity grid system as they also research the resources we use in the USA to generate electric power. This applies CCSS Literacy standard RST.11-12.2: Determine the central ideas or conclusions of a text; summarize complex concepts, processes, or information presented in a text by paraphrasing them in simpler but still accurate terms and Math Practice 3: Construct viable arguments and critique the reasoning of others. 

The NGSS performance standard HS-PS2-5: Plan and conduct an investigation to provide evidence that an electric current can produce a magnetic field and that a changing magnetic field can produce an electric current in applied to this lesson as are Science Practice 6: Constructing explanations (for science) and designing solutions (for engineering), Science Practice 7: Engaging in argument from evidence and Science Practice 8: Obtaining, evaluating, and communicating information.

Electric Generation

40 minutes

The goal of the lesson is for students to discover that a changing magnetic field is required to induce a current in a wire. They apply this understanding to label and explain the parts on a steam turbine.

I kick off this class with a commercial from Geico which shows hamsters row a boat to push water through a generator. This produces electricity so that the gentleman in the commercial can save money on his electric bill. The commercial is funny in that there are much easier ways to save money. Amazingly, few people really understand how electric power is produced on a large scale. Today, students figure out just how it happens. 

All students get the Generator PhET Lab handout. They work in groups of 2-3 as cooperative learning gives students a chance to talk through the assignment and to help each other. Each group gets a computer with internet access. They start with a search to define "electric motor" and "electric generator". They also research the different types of resources used to generate electricity in the United States. This information gives them a foundation to understand how electricity is produced on a large scale, which is dones with the PhET simulator titled Generator. There are different situations in this PhET simulator.  One has a magnet that can be moved around the simulator and a coil of wire attached to a light bulb. When you move the magnet through the or around the coil, you see a current flow through the wire and light the bulb. Another situation has a magnet positioned near a coil of wire. Above the magnet is a water source that you can turn on and cause the magnet to spin. The spinning magnet then induces an electric current in the coil. These simulators lead students through the discovery that a changing magnetic field can induce a current in a wire. 

While students are engaged in the activity, I walk around the room and monitor their progress. I also employ the Colored Cups strategy, which informs me of when students are in need of support.

The students have 35 minutes to complete the activity, as I like to spend the final 10 minutes of class reviewing. I use an online timer projected on the board so students know how much time is left.

Debrief on Generator Sheet

10 minutes

There are two big takeaways for this lesson:

  1. Changing magnetic field induces a current in a coil of wire.
  2. Generators that power a city work on the same concept as a small hand generator. The only question is how do you spin the magnets or coils relative to each other?

I collect the students work and use my document camera to review several work samples in the last 10 minutes of class. I go through and display correct answers provided on the sheets. The primary purpose is to make sure students understand the primary learning objective.

Then, using a hand generator, I demonstrate the generation of electric power. While there are dozens of designs of hand powered flashlights, this one is among the best for demonstration purposes, as students can see the magnet and coils of wire and see how the spinning causes the bulb to light. The flashlights with a covered motor are not nearly as effective because students can't see the coils of wire or magnets and how they move relative to each other. This generator can be purchased on Amazon.

In this lesson students learn that moving a coil of wire through a magnetic field creates a current. When it comes to providing the energy demands of our modern society, the big question is: How do we move the coils of wire through a magnetic field on a large scale? It takes many huge magnets and massive coils of wire all spinning around to power a city! In the US, 99% of our electric generation is done by heating water into high pressure steam which spins a generator. Today's lesson sets the stage for a future project where students research and do a project on the electric power grid.