Smartphone Magnetometer Field Mapping for Electromagnetism Mastery

TL;DR
Clamp a smartphone in a 3D-printed jig, sweep it through the axis of a solenoid, and log magnetic field strength with PhyPhox or Science Journal.
Plot B vs distance, overlay Biot–Savart predictions, and discuss discrepancies from edge effects and sensor drift.
You walk away with publishable graphs, rigorous uncertainty commentary, and compelling material for Paper 4 planning answers about electromagnetism experiments.

Why Bring Smartphones into the Magnetism Lab

• Examiner feedback highlights weak qualitative descriptions of magnetic-field mapping; high-resolution smartphone data solves that gap.
• Students see an authentic application of vector data logging — aligning with MOE's emphasis on digital fluency across science subjects.
• The activity dovetails with AC generator and induction experiments already on your blog, letting learners compare multiple electromagnetism contexts.

Apparatus Checklist

Experimental Workflow

1. Zero the sensor. Use the magnetometer app's calibration routine away from large ferromagnetic objects. Record residual offset.
2. Align the jig. Position the smartphone so its sensitive axis (usually the x- or y-axis) points along the solenoid's central axis.
3. Set current increments. Ramp current in 0.2 A steps and hold each setting steady for 10 s while logging.
4. Sweep positions. Move the phone along the axis from the solenoid centre out to at least three coil radii. Log background field with the supply off for subtraction.
5. Process data. Export CSV, subtract background, and compute theoretical B(z) = \frac{\mu_0 n I}{2}\left(\frac{z_2}{\sqrt{R^2 + z_2^2}} - \frac{z_1}{\sqrt{R^2 + z_1^2}}\right) for finite solenoids or the Helmholtz pair formula.
6. Discuss deviations. Highlight edge effects, sensor saturation, and misalignment. Quantify percentage differences at key points.

Enhancements and Differentiation

• Rotate the smartphone to capture radial components and construct vector field plots in Desmos or Python.
• Investigate hysteresis by inserting iron cores and repeating the sweep while describing safety precautions.
• Pair the rig with the Building an AC Generator guide to connect static field mapping with induction measurements.
• Offer an enrichment clinic where students compare smartphone data against Vernier or Pasco magnetic field sensors to validate reliability.

Reporting and Assessment Tips

• Include a calibration table and mention the app sampling rate to show command of data quality.
• Use logbook screenshots (with student names redacted) to evidence digital workflow for scholarship portfolios.
• Encourage students to narrate real-world applications (magnetic navigation, biomedical imaging) in their conclusion.

References

• Frontiers in Education, Smartphone sensors for physics education: a review, 10.3389/feduc.2020.00114
• PhET Interactive Simulations, Magnet and Compass
• Tortajada, M. et al., Surveying the magnetic field using smartphones, arXiv:2103.02615