How far away is infinity? An electromagnetic exercise to develop intuition regarding models

TL;DR

This paper presents an educational activity for university physics students that helps develop intuition about electric field models by comparing finite, infinite, and point charge fields, revealing common misconceptions.

Contribution

It introduces a practical activity to improve understanding of electromagnetic models and highlights students' misconceptions about field approximations.

Findings

Students often lack intuition about when to approximate a finite line as infinite.

Many students do not recognize the conditions under which fields resemble idealized models.

The activity improves students' understanding of electromagnetic field approximations.

Abstract

The estimation of the electric field in simple situations provides an opportunity to develop intuition about the models used in physics. We propose an activity aimed at university students of General Physics where the electric field of a finite line of charge is compared, analytically or numerically, with the fields of an infinite line and of a point charge. Contrary to intuition, it is not necessary to get very close for the line charge to be considered infinite, nor to move very far away for the finite line field to resemble that of a point charge. We conducted this activity with a group of students and found that many of them have not yet developed an adequate intuition about the approximations used in electromagnetism.