Hands-on Activity: Force on a Current Carrying Wire

Contributed by: VU Bioengineering RET Program, School of Engineering, Vanderbilt University

A photograph shows a female patient laying on a table getting ready to have an MRI as a medical support staff stands nearby.
An MRI machine uses magnetic force to make images of the human body.
copyright
Copyright © 2009 Celebration Health, Wikipedia http://en.wikipedia.org/wiki/File:Seaside_Imaging_Center_MRI.jpg

Summary

Students use a simple experimental setup consisting of a current-carrying wire and a magnet to explore the forces that enable biomedical imaging. In doing so, they run a current through a wire and then hold magnets in various positions to establish and explore the magnetic force acting on the wire. They move the magnets and change the current in the wire to explore how the force changes. They students apply what they have learned during the experiment to the challenge to create a safe working environment around MRI machines.
This engineering curriculum meets Next Generation Science Standards (NGSS).

Engineering Connection

An MRI machine uses magnetic force to make images of the human body. In the lab, we explore this magnetic force and its properties. In assessment questions 4 and 5, students are asked to apply what they have learned during the experiment to create a safe environment around MRI machines, which are the kinds of question engineers consider in the products they create.

Learning Objectives

After this activity, students should be able to:

  • Predict and test the direction of the magnetic force on a current-carrying wire.
  • Predict and test the effects of switching the direction of the current in the wire.

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Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

  • Develop and use a model of two objects interacting through electric or magnetic fields to illustrate the forces between objects and the changes in energy of the objects due to the interaction. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Medical technologies include prevention and rehabilitation, vaccines and pharmaceuticals, medical and surgical procedures, genetic engineering, and the systems within which health is protected and maintained. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Technological innovation often results when ideas, knowledge, or skills are shared within a technology, among technologies, or across other fields. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Results of scientific inquiry--new knowledge and methods--emerge from different types of investigations and public communication among scientists. In communicating and defending the results of scientific inquiry, arguments must be logical and demonstrate connections between natural phenomena, investigations, and the historical body of scientific knowledge. In addition, the methods and procedures that scientists used to obtain evidence must be clearly reported to enhance opportunities for further investigation. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
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Materials List

Each group needs:

Introduction/Motivation

Thus far in class, we have learned that MRI machines use magnetic force to make images of the human body. In order to solve the MRI Safety Grand Challenge (as presented in the unit), we must now begin to understand the affects of such a magnetic force. In class we have learned that a magnetic field affects a current-carrying wire. This lab helps us to see and feel this force on a current-carrying wire. After this activity, you begin to consider the effects of an MRI machine on metal objects, which may impact the safety of medical personnel and patients.

Procedure

Before the Activity

  • Gather materials and make copies of the Force on a Current-Carrying Wire Handout.
  • Set up the lab stands with a foil ribbon, 6V battery and 1 ohm resistor connected in series by alligator clips, as shown in Figure 1.

A line drawing shows a foil ribbon strung between the tops of two ring stands. From each ring stand a wire is connected to a 6V battery, with a 1 ohm resistor along one of the wires.
Figure 1. The activity setup.
copyright
Copyright © 2006 Eric Appelt, Vanderbilt University

With the Student - Initial Thoughts

Prompt students to consider and respond to the following pre-lab questions, which are provided on the handout.

  1. Consider a positive current moving from left to right. Sketch four diagrams showing a magnetic field oriented up, down, into the page, and out of the page with arrows indicating the force on the wire.
  2. Find the current flowing through a wire connected to a 6V battery and a 1 ohm resistor. Then find the magnitude of the magnetic force on 1 cm wire if the strength of the magnetic field is 1000 Gauss and the current and field are oriented in any of the positions in the diagrams just drawn.

With the Students - Procedure

Divide the class into groups of two to four students each. Hand out the materials. Then direct students to follow this procedure, which is provided on the handout.

  1. Use the compass to determine the direction of the magnetic field in your permanent magnet, and use masking tape to mark this direction on your magnet.
  2. Attach 2 alligator clips near the tops of the lab stands with masking tape as shown in the diagram (same diagram as Figure 1).
  3. Cut a very thin ribbon of aluminum foil from your sheet, and attach this to both clips on the tops of the lab stands.
  4. Complete a circuit as shown on the diagram, so that the conventional current is flowing from left to right.
  5. With the permanent magnet, try creating a field near the wire in each of the four orientations that you sketched, and note the behavior of the wire in each orientation.
  6. Switch the connections to the positive and negative terminals of the battery, and repeat the previous step.

Conclude by assigning students to answer the five questions at the end of the handout.

Attachments

Assessment

Post-Activity Assessment: At the conclusion of the lab, have students answer the five questions at the end of the Force on a Current Carrying Wire Handout to apply what they have learned to the MRI Safety Grand Challenge and towards drawing engineering connections. Review their answers to gauge their comprehension of the subject matter.

  1. Describe the behavior of the wire in each orientation, and state whether you saw evidence of a force on the wire in the direction expected.
  2. Explain the change in the current when you switched the battery connections, and how this affected the behavior of the wire.
  3. While conventional current is thought of as positive charge moving from higher to lower potential, in reality negative charge (electrons) are moving from lower to higher potential. Explain why this should not affect your predictions or results.
  4. How is this related to an MRI machine?
  5. What have you learned during this experiment about creating a safe environment around an MRI machine?

Contributors

Eric Appelt

Copyright

© 2013 by Regents of the University of Colorado; original © 2006 Vanderbilt University

Supporting Program

VU Bioengineering RET Program, School of Engineering, Vanderbilt University

Acknowledgements

The contents of this digital library curriculum were developed under National Science Foundation RET grant nos. 0338092 and 0742871. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.

Last modified: September 7, 2017

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