Unit 2: Environmental Magnetism

Compiled by Klaudio Peshtani (kpeshtani@gmail.com) and Lee Slater (lslater@newark.rutgers.edu), Rutgers University Newark

Last updated: 9/7/2023

Summary

The narrated video explores the basics of magnetism.

This module introduces students to the underlying principles of magnetism and its application in environmental investigations. Students are introduced to major concepts on magnetism through a narrated video that covers: [1] environmental issues where magnetic geophysical surveys can help; [2] types of magnetism; [3] magnetic fields generated by magnetic objects; and [4] the Earth's magnetic field.

Concepts are reinforced through a worksheet that allows the student to simulate changes in the magnetic fields around two magnets and to explore the properties of the Earth's magnetic field as a function of position. Students will then explore the significance of a magnetic dataset acquired as part of an archaeological survey.

The archaeological survey was conducted over the grounds of a 17th-century home in New Jersey where Dutch settlers are believed to have kept enslaved persons. Students are provided with an online Python script to visualize the data and are guided in some simple processing steps to help with the interpretation of the survey results. A worksheet is provided to reinforce these concepts and to encourage students to think creatively about the dataset.

In the concluding segment, students will receive guidance on utilizing a freely available app that can transform their smartphones into magnetometers. They will then proceed to conduct their own distinctive magnetic survey on a personalized grid, which will be prepared by the instructor. The results of the survey will be plotted using a distinct online Python script (accessible here), eliminating the need for any specialized software.

Exploration Methods, Environmental Science

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Learning Goals

Students will be able to:

Describe the fundamental principles of magnetism and how they may be applicable to environmental concerns (e.g., abandoned oil and gas wells)
Visually interpret magnetic force through the use of an interactive online simulator
Explain how the physical properties of soils and rocks can influence magnetism
Produce a 2D magnetic intensity plot with Python using raw measurements from a real magnetics survey
Generate a 2D magnetic intensity plot with Python using data collected from their own magnetics survey using a free downloadable phone app

Context for Use

This unit is designed as a guided learning project that is best used as an introductory lab. The target audience is first-year or sophomore earth and environmental science students with little prior experience with near-surface geophysics and data processing. However, the materials could be adapted and used by faculty teaching an upper-level undergraduate course in geophysics. The materials needed to use this unit are all available from embedded links. The material in this unit should complement the third unit of this module, which focuses on the application of magnetic (and gravity) datasets.

Description and Teaching Materials

The teaching materials for this project include a student handout (Microsoft Word 2007 (.docx) 89kB Sep1 23), a student worksheet (Microsoft Word 2007 (.docx) 1.3MB Sep7 23), a narrated video, an online Python script with data from a magnetometer survey, and a separate online Python script using data collected by students in the cellphone magnetics survey. The worksheet includes external links to sites that contain animations and magnetic field calculators to reinforce concepts. The student works through four main tasks, following instructions provided in the handout and answering questions in the worksheet. The four tasks, and materials used in each task, are summarized below.

Task 1: Environmental Concerns & Magnetism

Narrated video (Part 1: Environmental Magnetization)
Student worksheet (Task 1)

Task 2: How magnetism can be used to solve urban and environmental problems

Narrated video (Part 2: Environmental Magnetization)
Student worksheet (Task 2) with external links

Task 3: Creating a 2D magnetic survey plot using real magnetic survey data

Student worksheet (Task 3)
Online Python script (Using existing data from a real magnetics survey)

Task 4: How you can run a magnetics survey with your cell phone!

Student worksheet (Task 4) with external links, including a downloadable cell phone app
Online Python script 2 (Using the student's data from their cellphone magnetics survey)

Teaching Notes and Tips

This module is designed to be flexible and suitable for an introductory-level science class and requires no software or specialized instrumentation. Given the intended audience, the mathematical content in this module is kept to a minimum. Use of the online Python script has been simplified to the fullest extent possible, with students required to make only a few, carefully guided, changes to the provided code. However, it should still give students an appreciation of how computer programming is used to process geoscience datasets.

Cellphone Magnetometer Survey:

The cellphone magnetometer survey portion of this module is intended to be customized according to the instructor's preference and can be expanded or minimized to accommodate any size. The following notes outline a suggested example setup; however, can be adjusted to any extent as needed.

The cellphone magnetometer app "Metal Detector" is freely downloadable for iOS or Google Play.
- The magnetometer in a smartphone is typically located near the camera.
- To calibrate the cellphone magnetometer, rotate the phone above head in the shape of a circle for a few seconds.
- A selfie stick is a convenient tool to make measuring easier, however, is not necessary.
The instructor will need to create a grid with their preferred dimensions, adding hidden magnetic anomalies along any coordinates of their choice.
- The grid size and measurement increments can be adjusted according to preference. Opting for larger grids (e.g., 20 x 20 meters) is advisable for replicating realistic magnetic surveys and will also extend the time required for completion.
- If you wish to modify the grid dimensions, alter the grid details under "🧲 Survey Details" in your instructor copy of the IGUaNA Smart Phone Magnetics script. Ensure that the instructor's Google Sheets copy (accessible from the script) and printable data recording sheet.docx (Microsoft Word 2007 (.docx) 42kB Sep3 23) are updated to accommodate for changes in the X and Y dimensions.
Create two sets of marker flags that will act as a reference marker on the grid for students to measure using their cellphone magnetometer:

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Demonstration of how to create magnetic or non-magnetic marker flags using a wooden dowel/stake, red tape, and a magnet.
Provenance: Klaudio Peshtani, Rutgers University-Newark
Reuse: If you wish to use this item outside this site in ways that exceed fair use (see http://fairuse.stanford.edu/) you must seek permission from its creator.
1. Non-magnetic marker flags: Wrap a wooden dowel or stake with colored duct tape (preferably red/light colors), creating a flag (see figure). 6-inch dowels are recommended so the marker flag is as close to the ground as possible.
2. Magnetic marker flags: Place a small magnet next to the wooden dowel or stake and encase it by wrapping colored duct tape around it (see figure). The magnetic marker flags will look identical to the non-magnetic marker flags. You can place these magnetic anomalies at any preferred point along the grid. It is recommended that you vary the amount of magnetic material hidden in each magnetic marker flag to create a more diverse contour plot.
The illustration to the right presents an example of a 5x5 meter grid, with measurements taken at 0.5-meter intervals and marker flags positioned every meter (for student convenience, marker flags can also be placed at each measurement point).

Students will work in teams of two to ensure all students are actively participating in the survey. Student one will be measuring data with their cellphone magnetometer and relaying it to the recorder (student two), who will be recording the magnetic data at the corresponding grid coordinate on the printable datasheet provided. Utilizing this datasheet, students will then generate individualized 2D magnetic contour plots by utilizing the provided Python script.
- Direct students to form a line at point 0 (X) 0 (Y) on the grid with their paired partner. After the first pair completes at least two meters of measurements, direct the next pair to start to avoid clustering.
- It is recommended that students rotate between roles as the measurer or recorder in their paired groups.
- Recommend students to download the cellphone magnetometer app prior to relocating/beginning the survey to avoid troubleshooting during the survey.

Assessment

The student worksheet is designed to help evaluate whether students have grasped the main concepts related to Tasks 1-4 of this unit on environmental magnetism. Note: This file is also linked above, in the Teaching Materials section of this page.