Magnetic latitude
Measure your reaction time with visual and audio stimuli
Author:
Title 4
Learning objectives :
This activity allows students to determine their magnetic latitude from measurements of the Earth's magnetic field. It develops the understanding of terrestrial magnetism and geographic coordinates.
Concepts covered
Earth's magnetic field; Magnetic tilt; Latitude and longitude; Magnetic dipole model; Magnetic declination
What students will do :
The student measures magnetic tilt using the FizziQ magnetometer and inclinometer simultaneously in Duo mode. By analyzing the horizontal component of the magnetic field and the angle of inclination relative to the horizontal, the student can calculate their magnetic latitude using a formula and then understand the difference between magnetic and geographic coordinates.
What is required :
Smartphone with the FizziQ application; Environment free from magnetic disturbances; FizziQ experience notebook; Calculator for trigonometric calculations
Scientific background :
The Earth's magnetic field resembles that of a dipole inclined about 11° relative to the axis of rotation. This configuration explains why the magnetic inclination (angle between the magnetic field and the horizontal) varies with latitude. At the magnetic pole, the inclination is 90° (vertical field); at the magnetic equator, it is 0° (horizontal field). Between these two extremes, the inclination i can be approximately related to the magnetic latitude L by the formula: tan(i) = 2×tan(L). This relationship follows from the mathematical model of the Earth's magnetic dipole. The smartphone's magnetometer measures the components of the magnetic field along three axes. The Y (horizontal) component is maximum when the device is oriented towards magnetic north. The inclinometer measures the angle between the smartphone and the horizontal. By correctly orienting the device, the local magnetic inclination can be determined. Calculated magnetic latitude generally differs from geographic latitude for two reasons: 1) The offset between the magnetic and geographic poles (the magnetic north pole is currently in the Canadian Arctic, at approximately 86.5°N, 170.9°E); 2) Local magnetic anomalies due to the composition of the subsoil. These measurements make it possible to concretely understand the three-dimensional structure of the Earth's magnetic field. Historically, the discovery of magnetic inclination is attributed to Georg Hartmann (1544), but Robert Norman was the first to measure it precisely (1581). The experiment conceptually reproduces that of the explorer James Clark Ross who located the north magnetic pole in 1831 by following variations in inclination.