Should I Unplug?

This page is authored by Lori Carmack of Salisbury University, inspired by a presentation by Victor Donnay, Bryn Mawr College, at the 2013 MAA PREP Workshop: USE Math on Your Campus at Shippensburg University. Workshop organizers: Corrine Taylor (Wellesley College), Ben Galluzzo (Shippensburg University), James Hamblin (Shippensburg University).

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A wide variety of electronic devices and small appliances are a regular part of students' lives: cell phones, laptops, iPods/MP3 players, hairdryers, irons, coffeemakers, printers, mini-refrigerators, microwaves, televisions, etc. Many of these products remain plugged in while not in use in students' dorms or apartments, still drawing power. This unnecessary use of energy is known as standby, phantom, or vampire power, and has recently become a global issue. The International Energy Agency estimated that in 2007, standby power was responsible for 1% of the world's carbon dioxide emissions; in contrast, air travel contributed less than 3%. Furthermore, some studies estimate that standby power accounts for as much as 13% of consumer electrical use (see references below, particularly the first link in Number 2). In this project, students investigate the question "Should I unplug?" In particular, during an in-class activity, students measure plug loads (the amount of energy used by electronics) of several electrical products using a wattage meter, then learn how to convert electrical usage to an equivalent dollar value. Afterward, students are assigned a group project focused on the monetary costs associated with phantom loads. Students present results of their investigations via an oral presentation.

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Learning Goals

In this activity, students learn about plug loads, measure plug loads of various electronic devices and small appliances using a wattage meter, better understand conversion factors, and learn to translate standard AC electrical usage into an equivalent dollar value. In addition, they think about the broader implications of unnecessary energy consumption, and prepare and present the results of their investigations.

Context for Use

This activity requires only basic computational skills and is intended for small groups. It is based on a National Energy Education Development (NEED) Project ( The NEED Project is designed for the intermediate and secondary level; this activity is appropriate for a math for liberal arts or quantitative reasoning course at the collegiate level. The project should take approximately one week and consists of three parts: a) an in-class activity and preliminary example calculation, b) independent student research and calculations, and c) a summary presentation. Necessary equipment for the in-class portion includes a wattage meter, students' cell phones with chargers, and/or various other small appliances and electronic devices. Plug loads for many products can be found online (see sample links in the below "References and Resources" section).

Description and Teaching Materials

The included file contains some background, a description of the in-class activity, a sample calculation of converting wattage into an equivalent dollar value, an out of class group project, and a presentation rubric.

In-Class Activity and Group Project for Analyzing Phantom Loads (Microsoft Word 2007 (.docx) 19kB Aug14 18)

Teaching Notes and Tips

For the in-class activity, it is useful to supply several wattage meters, and to have students bring electrical devices such as cell phones, music players, laptops, tablets, etc., and their chargers to class. It is also suggested to provide some small electrical products such as a hair dryer, coffeemaker, etc. A crucial component of the project is to carefully walk students through a sample calculation converting wattage usage into an equivalent dollar value during the in-class activity.


Students will be assessed based upon a final presentation of their research, including the accuracy of their calculations, and their answer the question "Should I unplug?" See In-Class Activity and Group Project for Analyzing Phantom Loads (Microsoft Word 2007 (.docx) 19kB Aug14 18) for a suggested rubric.

References and Resources