---
title: "An electron travels through a region containing uniform, static electric and magnetic fields. Over a short time interval, the electron follows a curved path and emerges with a kinetic energy greater than its initial kinetic energy. Two students debate which field contributed to the increase in the electron’s speed. Which of the following explanations correctly evaluates the work done on the electron by the fields?"
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url: "https://nerd-notes.com/ubq/123145/"
date_modified: "2026-09-28T11:57:40+00:00"
---

# An electron travels through a region containing uniform, static electric and magnetic fields. Over a short time interval, the electron follows a curved path and emerges with a kinetic energy greater than its initial kinetic energy. Two students debate which field contributed to the increase in the electron’s speed. Which of the following explanations correctly evaluates the work done on the electron by the fields?

An electron travels through a region containing uniform, static electric and magnetic fields. Over a short time interval, the electron follows a curved path and emerges with a kinetic energy greater than its initial kinetic energy. Two students debate which field contributed to the increase in the electron's speed. Which of the following explanations correctly evaluates the work done on the electron by the fields?

- **A.** Only the electric field does work on the electron, because the magnetic force is always perpendicular to the electron's instantaneous velocity, whereas the electric force has a component along the electron's displacement.
- **B.** Both the electric and magnetic fields do work on the electron, because any force that accelerates a charged particle along a curved path contributes to the net work required to change its kinetic energy.
- **C.** The magnetic field does work only when the electron is deflected across magnetic field lines, while the electric field does work only when the electron moves parallel to the electric field lines.
- **D.** Only the magnetic field does work on the electron, because the electric field merely establishes an electrostatic potential that guides the particle while the Lorentz magnetic force provides the physical push.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123145/*