Magnetometry at home: a hands-on survey with your smartphone

Carl-Georg Bank, University of Toronto

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Summary

Using a free app downloaded to their smartphone or tablet device students engage in collecting magnetic field data. Students have to design and document a survey, and are encouraged to do simple quality control. The survey can be done within the confines of their home, or outside in a driveway, a parking lot, or a park. The intention is for students to see the object causing the anomaly and measure a profile towards or over it. The activity is suitable as an introductory activity for a virtual field course, or as preparation for an in-person field course, or as exercise in an introductory geophysics course.

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Context

Audience

This activity may be used as
- introduction to the magnetic method in an introductory geophysics course,
- a preparation before heading to field camp, and/or
- activity to include in a virtual geophysics field camp.

Skills and concepts that students must have mastered

It will be helpful if students know about the dipole nature of magnetic fields. Students do not need to know about magnetic surveys in geophysics -- although the activity was developed within the context of a geophysics course -- and thus this activity can be adapted to focus on note-taking and documenting a survey.

How the activity is situated in the course

This is a stand-alone activity, to be done either at the start of the course (to stress note-taking skills) or to introduce the magnetic method and simulate a survey.

Activity Length

Students should budget 3 hours to complete this activity.

Goals

Content/concepts goals for this activity

At the end of this activity students will be able to:
1. select a target and design a magnetic survey,
2. collect field data ("field" being very broadly defined) with a free app,

Higher order thinking skills goals for this activity

3. document their survey,

4. graph the data they obtain,

5. complete a simple quantitative analysis, and

Other skills goals for this activity

6. communicate their findings.

Description and Teaching Materials

Students complete a step-by-step worksheet. Their target can be a fridge magnet, an iron chair, a parked vehicle, a fence. The intention is for students to see the object and explicitly measure a magnetic profile. They need a smartphone or tablet device (iOS or Android) and a measuring tape is helpful (but not crucial).

student_worksheet_MagnetometryAtHome.docx (Microsoft Word 2007 (.docx) 112kB Apr24 21): is the worksheet for students to complete

example_MagnetometryAtHome.pdf (Acrobat (PDF) 384kB Apr24 21): provides an example of a completed worksheet

sample data (Excel 2007 (.xlsx) 82kB May20 20): is the spreadsheet with the raw data and analysis for the example worksheet

Technology Needs

Students need to download and install the magnetometer app from the Physics Toolbox: https://www.vieyrasoftware.net/ to their smartphone or tablet (Android or iOS). Once they have this app installed they do not need internet access. However, the activity asks them to determine their GPS location using their smartphones. I suggest they use a spreadsheet to plot and analyse their data.

Teaching Notes and Tips

I have tried this activity with students.

  • Students seemed to be able to complete this task on their own within a two-hour block; some targets were a TV or laptop, a parked vehicle, a buried cable, even a cased firearm.
  • It will be helpful for students to see the example of a completed workbook (included in this activity).
  • I have found in field courses that students need reinforcement about how to document their surveys, therefore Task 3 is quite extensive. It will be helpful to have students discuss documentation when in the field, or let them ask for such information as you provide them with data but not all the information that should go with it.
  • Students may not have sufficient background to tackle task 7, especially task 7b (matching recalculated distances and magnetic field values to a theoretical curve). This task could be left out, or addressed later with the whole class.
     

Assessment

The worksheet includes a single-point rubric. It lists my expectations for the "competent" level, while leaving spaces for "developing" and "excellent". I prefer to not provide a full rubric because (1) it encourages a discussion with my students what we as a group will consider "excellent" and (2) it also provides the opportunity for individual feedback given that students can run very different surveys. For more on single-point rubrics, check eg. https://teaching.cambriancollege.ca/assess/rubrics/single-point/

References and Resources

MagnetometryAtHome_background.docx (Microsoft Word 2007 (.docx) 12kB Apr24 21): provides short answers to the questions in the "background" or "looking forward" sections of the worksheet.




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