← All Lesson Plans
Lesson Plan

The Hall

1879 Baltimore • In June 2026 a team led by Dongchen Qi (Queensland University of Technology) and Xiao Renshaw Wang (Nanyang Technological University, Singapore) published in the journal Newton a study of the nonlinear Hall effect in the topological insulator Bi2Te3, showing it produces a direct-current transverse voltage from an alternating current with no external magnetic field, survives at room temperature, and is controlled by skew scattering from impurities and phonons, pointing toward battery-free energy harvesting that rectifies ambient radio-frequency signals into usable power. •
Before using this lesson plan: Read the full story or listen to the 5-minute narration (works as a bell-ringer).
Quick Use (jump to the section you need)
Key Concepts and Vocabulary Assessment / Discussion Prompts Cross-curricular Extensions

The Hall: Lesson Plan

Overview

This lesson uses Edwin Hall's 1879 discovery of the Hall effect, made as a graduate student who doubted a single sentence in Maxwell's textbook, to explore the magnetic force on moving charges, how we know the sign of a current's carriers, and how a curiosity-driven measurement becomes foundational technology. Students connect Hall's original experiment to the 2026 discovery of a room-temperature nonlinear Hall effect in bismuth telluride, which produces a transverse voltage with no magnetic field at all and points toward battery-free electronics.

Subject areas: Physics, Electronics, History of Science, Engineering Grade levels: 9-12, AP Physics 2, introductory college physics Duration: 1-2 class periods (45-90 minutes)

Essential Questions

  1. What force does a magnetic field exert on a moving electric charge, and in which direction?
  1. Why does a current-carrying conductor in a magnetic field develop a voltage across its width?
  1. How can the sign of the Hall voltage reveal whether the charge carriers are positive or negative?
  1. How did Hall measure a property of the electron eighteen years before the electron was discovered?
  1. What is different about the nonlinear Hall effect of 2026, and why does needing no magnet matter for powering devices?

Learning Objectives

Students will be able to:

  • State the magnetic (Lorentz) force on a moving charge and predict its direction with the right-hand rule
  • Explain why charges accumulate on one edge of a current-carrying strip in a perpendicular magnetic field, producing the Hall voltage
  • Use the sign of the Hall voltage to deduce the sign of the charge carriers
  • Explain why a thin conductor makes the effect easier to measure
  • Describe, qualitatively, how the nonlinear Hall effect can rectify alternating current into direct current without a magnetic field, and why that enables energy harvesting

Key Concepts and Vocabulary

  • Magnetic (Lorentz) force: the sideways force a magnetic field exerts on a moving charge, perpendicular to both the velocity and the field.
  • Hall voltage: the transverse voltage that appears across a current-carrying conductor placed in a perpendicular magnetic field.
  • Charge carriers: the particles (usually electrons; sometimes effectively positive "holes") that carry current in a material.
  • Holes: vacancies in a nearly full band that behave like positive carriers, explaining why some materials show a reversed Hall sign.
  • Topological insulator (Bi2Te3, bismuth telluride): a material that conducts on its surface with special symmetry properties exploited by the nonlinear Hall effect.
  • Rectification: converting alternating current (AC) into direct current (DC).
  • Energy harvesting: capturing small amounts of ambient energy (for example, stray radio waves) to power electronics.

Activities

  1. Right-hand-rule warm-up (10 min). Given a current direction and a magnetic field direction, students predict which edge of a strip the electrons drift toward, then predict the polarity of the Hall voltage. Repeat for positive carriers and note the reversal.
  1. The thin-strip insight (10 min). Students reason about why a thicker conductor dilutes the effect and why Hall used gold leaf. Connect cross-sectional area to carrier density and drift velocity.
  1. Reading a textbook critically (15 min). Present Maxwell's actual sentence and Hall's objection. Discuss: how do you tell the difference between a claim you should accept and one worth testing? What experiment would settle it?
  1. From sensor to power source (15 min). Compare the 1879 Hall effect (needs a magnet, used to measure) with the 2026 nonlinear Hall effect (needs no magnet, used to rectify and harvest energy). Students sketch where a battery-free sensor might be useful.

Assessment / Discussion Prompts

  • Draw a current-carrying strip in a magnetic field and label the carrier motion, the magnetic force, the charge build-up, and the Hall voltage polarity.
  • Explain how Hall's result contradicted Maxwell, and why the second edition of the Treatise added a footnote.
  • A material shows a Hall voltage of the "wrong" sign. What does that tell you about its carriers?
  • Why is "no magnetic field required" the crucial feature that lets the nonlinear Hall effect power a small device?

Cross-curricular Extensions

  • History of science: how scientific authority and correction work; a student correcting Maxwell.
  • Engineering: survey real Hall-effect sensors (automotive, current sensing, position sensing) in everyday devices.
  • Mathematics: linear versus nonlinear (second-order) response, and why a quadratic response can rectify AC to DC.

About Time Rhymes Lesson Plans: Every lesson plan is generated alongside the story and aligned with the C3 Framework for Social Studies. The story itself is independently fact-checked with a full evidence manifest. All materials are free to use in the classroom.

Questions or suggestions? daily@timerhymes.com