Orient yourself with a magnetometer!
Make a digital compass with your smartphone
Author:
Title 4
Learning objectives :
This activity allows students to understand how a compass works and to use the smartphone's magnetometer to orient themselves. It develops the understanding of the earth's magnetic field and its practical applications.
Concepts covered
Earth's magnetic field; Orientation; Magnetic and geographic north; Magnetometer; Horizontal component of the field
What students will do :
The student uses the FizziQ magnetometer to determine the direction of magnetic north. By measuring the horizontal component of the earth's magnetic field in different orientations, the student identifies the direction where this component is maximum corresponding to magnetic north and then compares his result with the indication of a traditional compass.
What is required :
Smartphone with the FizziQ application; A classic compass for comparison (optional); A space without magnetic disturbances; FizziQ experience notebook
Scientific background :
The Earth's magnetic field, generated by the movements of the Earth's outer core, acts as a huge magnetic dipole, creating a field of approximately 25-65 µT at the surface. This field is oriented approximately toward the geographic poles, but with a significant offset: the magnetic north pole is currently in the Canadian Arctic. The Earth's magnetic field has both a horizontal and a vertical component. The horizontal component, parallel to the earth's surface, is the one that allows orientation: it points towards magnetic north. The smartphone's magnetometer measures the magnetic field along three orthogonal axes (X, Y, Z) with a sensitivity of approximately 0.1 µT. To determine the direction of magnetic north, simply rotate the smartphone horizontally and identify the orientation where the Y component of the field is maximum (assuming the phone's Y axis is pointing toward the front of the device). This is precisely the principle used by traditional compasses, where a magnetic needle naturally aligns with the lines of the Earth's magnetic field. Potential difficulties include: 1) Local magnetic disturbances from metallic objects or electronic devices; 2) The calibration of the magnetometer which can drift over time; 3) The limited accuracy of the sensor (generally ±2-3°). This simple experiment allows us to understand the fundamental principle of orientation by magnetism, a technique which revolutionized navigation long before the invention of GPS. It also provides an opportunity to discuss the difference between magnetic north and true north, as well as magnetic declination which varies depending on position on the globe.