Measuring the Inclination and Declination of the Earth's magnetic field with a smartphone

Avradip Ghosh, University of Houston-University Park
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Initial Publication Date: December 7, 2020 | Reviewed: August 4, 2022

Summary

The poles of the Earth's magnetic field are not precisely aligned with the geographic north and south poles and, in fact, vary continuously. This activity introduces to students the Earth's magnetic field and how to measure the Magnetic Declination and Inclination at home with nothing but a smartphone. Every modern smartphone has an inbuilt 3-component magnetometer that it uses for efficient navigation. Using a free app called "Physics Toolbox Magnetometer", the smartphone magnetometer measurements can be accessed in real-time and measured. The activity involves taking measurements of the 3-components of the Earth's Magnetic field (Bx, By, and Bz) as a function of angle with respect to the Geographic North. By analyzing the data, one can obtain the Magnetic Declination, Inclination, and Magnetic Intensity (total magnetic field) of Earth's Magnetic field at the experimentation venue.

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Context

Audience

This activity can be performed by all students having some Science background. Preliminary high-school level knowledge of Science is all that is required. This activity was developed especially for a course on geophysical field methods, required for geophysics majors but accessible by most science or engineering students at the junior level. The activity was developed when the COVID19 pandemic prevented the typical residential field program from being held, so it was taught online instead. No additional money has to be spent by a student as it can be performed by a smartphone and from their homes' convenience.

Skills and concepts that students must have mastered

A brief understanding of Magnetics and vectors will be helpful but not necessary. All necessary information about the Earth's magnetic field is provided in the material. Links to websites and online information are also provided if the students desire to learn more in detail.

How the activity is situated in the course

This can be performed as a stand-alone experiment. It can also be incorporated into a virtual Geophysics Field camp or with other activities involving magnetics.

Activity Length

Ideally, the whole activity which includes analysis of the data should not take more than 1hour 30mins. Magnetic field measurements using a smartphone takes about 15-30 mins at max.

Goals

Content/concepts goals for this activity

Students will be able to:

  • Measure the 3-component profile of the Earth's magnetic field as a function of angle with the geographic north
  • Calculate the magnetic intensity
  • Calculate the angle of inclination/dip-angle of the Earth's magnetic field
  • Calculate the angle of declination of the Earth's magnetic field
  • Verification of results with the precise measurements done by the National Oceanic and Atmospheric Administration (United States) (NOAA) or similar, obtained through their websites.

Higher order thinking skills goals for this activity

  • Understanding Earth's Magnetic field
  • Understanding vectors in 3-D
  • Evaluate errors, uncertainties, and overall quality of the experiment; articulate reasons for errors and deviation from theoretically expected results
  • Plot Graphs in Excel or similar software

Other skills goals for this activity

  • Be able to use the "Physics Toolbox Magnetometer" app.
  • Be able to analyze data and communicate observation and results of the experiment through a scientific report.

Description and Teaching Materials

All detailed explanation of the activity is included in the supplementary instructions pdf and the excel file attached. This includes exhaustive information about the experiment setup, how to take measurements, and the analysis of the data.
An excel sheet is also attached that includes the measurements and the graphs plotted. Students can directly use this excel sheet to plot their graphs if desired.
Magnetic inclination and declination activity instructions (Acrobat (PDF) 2.4MB Dec4 20)
Magnetic inclination and declination experimental data and plots (Excel 2007 (.xlsx) 29kB Dec4 20)

Technology Needs

  • Any modern smartphone (IOS or Android)
  • Access to the internet for downloading the free app "Physics Toolbox Magnetometer" available in the App Store (IOS) or Play Store (Android).
  • Excel or any similar graph plotting software
  • Access to the internet for verification of results with the precise measurements done by the National Oceanic and Atmospheric Administration (United States) (NOAA) or similar, obtained through their websites.

Teaching Notes and Tips

  • Care should be taken to keep the experimentation area free of other magnets and varying magnetic fields such as that from other electronic devices such as speakers
  • Advisable to perform the activity preferably indoors as measurements take a considerable amount of time, and a stable environment is necessary. As long as the survey location is free from time-varying EM-field, there will be no problem. (this can be checked by opening the Physics toolbox magnetometer app, and if the readings flatline (become constant) after some time, then there is no time-varying magnetic field nearby)
  • If your smartphone/tablet has any cover/case, metal strips/magnets, consider removing it. (Mandatory for metal cases as it will interfere with signal)

Assessment

The activity can be evaluated by the accomplishment of the survey as documented with pictures, video, a report, and data. The quality and completeness of the graphs can be assessed. Comparisons can be made with the precise values obtained from the NOAA website, though keeping in mind wide variations can be possible. Some measure of the level of difficulty, creativity, and usefulness of the survey could be assigned.

References and Resources

All links to additional resources are provided in the main supplementary file attached.

Special thanks to the activity designed by Chris Rowan, Kent State University-Main Campus
titled: "Getting to know your smartphone magnetometer"
https://serc.carleton.edu/NAGTWorkshops/online_field/activities/237566.html

This activity would not have been possible without the inspiration of the above.




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