Transformers: More Than Meets the Eye

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Objective

Students read about alternating current and experiment with transformers so that they can solve word problems involving transformers.

Big Idea

A transformer, which is two separate coils of wire in close proximity to each other, changes the voltage of an alternating current by the same ratio as the two coils of wire.

Context and Supplies

Today, students read about alternating current and use a simulator to discover that electric transformers only work with alternating current. This builds off past lessons on electric generators and the energy transformations in a circuit.

Students need computers and access to the internet for this lesson as they are to use the Generator PhET simulation (PhET provides a series of high quality physical science simulators and is provided by The University of Colorado). Students also learn about the transformer formula which sets the ratio of the input voltage to output voltage equal to the ratio of the number of turns on the input coil to the output coil. Transformers are an essential part of our electric power grid and students should know about them for the unit's final assignment, The Power Grid Project.

NGSS applied for this lesson include the engineering standard HS-ETS1-4: Use a computer simulation to model the impact of proposed solutions to a complex real-world problem with numerous criteria and constraints on interactions within and between systems relevant to the problem and 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.  Science Practice 2: Developing and using models, Science Practice 5: Using mathematics and computational thinking, Science Practice 6: Constructing explanations (for science) and designing solutions (for engineering) and Science Practice 8: Obtaining, evaluating, and communicating information are also used.

CCSS applied; Math Practice 2: Reason abstractly and quantitatively, Math Practice 4: Model with mathematics and RST.11-12.4: Determine the meaning of symbols, key terms, and other domain-specific words and phrases as they are used in a specific scientific or technical context relevant to grades 11-12 texts and topics.

Observations of a Transformer Cover

5 minutes

As class begins, I collect the homework that was assigned last lesson, Conservation of Energy Revisited. The assignment is watch a 5 minute YouTube video, Energy 101: Electricity Generation, and create a one-page visual that shows how electricity gets to their homes from a power plant.  I revisit this assignment at the end of this lesson.

To get students into the topic of transformers, I start off with an observation exercise. Students are grouped in fours and each group has a small white board. I use my Document Camera to display a close-up of the print stamped on a Transformer. Based on the information written on the transformer, they have one minute to write down what they believe is the purpose of this device. 

After the one minute is up, I have a representative from each table share out their Observations of Transformer Cover. Replies such as it changes 120 volts AC into 6 volts DC and it operates with 15 watts of power are the primary answers I want to focus on for this exercise. 

Before students read about transformers and to figure out how they work, I want them to know that the primary task of a transformers is to either step up or step down a voltage.

Transformer Online Simulator Activity

30 minutes

This is a self-paced activity where students read about Alternating Current and Direct Current and how a transformer changes voltage. They also make observations on the PhET Generator simulation to figure out that transformers only operate with AC. Finally, students look up the transformer formula and apply the formula to solve word problems. 

All of this is on the Transformer PhET Activity handout. Students have a computer with internet access and physics textbooks available to use a resource. Each student gets their own handout, however, they work in groups of 2-3 to complete the activity. As a cooperative learning exercise, students have a chance to talk through the assignment and to help each other. I don't like to have groups bigger than 3; the smaller grouping makes it more likely that all students make significant contributions to the assignment. 

While students engage in the activity, I walk around the room and monitor their progress. I also employ the Colored Cups 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 reviewing. I use an online timer projected on the board so students know how much time is left. 

After 25 minutes, I collect the students work and review the solutions to the transformer word problems, Transformer Solutions. Then we go through the short Transformers power point on which students take notes. The power point contains the transformer formula along with a sample problem. Though this is a repeat of what students taught themselves a few minutes earlier, it is worth repeating. I also want this information in their notebooks as a resource.

Power Grid Overview

5 minutes

In the last few minutes of class, I set the stage for the Power Grid Project. I display the Power Grid Overview which is a display that is similar to what students make for the project. I also show actual pictures of the components on the overview which include high voltage lines, distributions lines and transformers. The pictures are all images from our city with which students are famiiar. For instance, when the picture comes up of the distribution transformer, at least one student shouts out, "Hey, I know where that is. It's on Triangle Street!"