Light intensity does not always decay with the inverse of the square of the distance: an open-inquiry laboratory

TL;DR

This paper presents an open-inquiry laboratory using smartphone sensors to experimentally challenge the traditional inverse-square law of light intensity decay, demonstrating that under certain conditions, intensity can decay linearly or remain constant.

Contribution

It introduces a low-cost, accessible laboratory setup that enables students to explore and question the limits of the inverse-square law in physics.

Findings

Light intensity can decay linearly or stay constant over certain distances.

Smartphone sensors effectively measure diverse light source intensity curves.

The experiment encourages critical thinking about physical laws.

Abstract

The square inverse law with distance plays an important role in many fields of physics covering electromagnetism, optics or acoustics. However, as every law in physics has its range of validity. We propose an open-inquiry laboratory where we challenge these concepts by proposing experiments where the intensity of light decays linearly or even remains constant over a range of distances. Using the light sensors built into smartphones, it is possible to measure light curves for different sources: point, linear, planar and even LED ring lights. The analysis of these curves allows us to discuss the limits of the physical theories. This low-cost laboratory, initially proposed in the context of the COVID19 pandemic, has the virtue of challenging intuition and encouraging the critical spirit of the students.