High accuracy optical inverse square law experiment using inexpensive light to frequency converters
Keith H. Wanser, Steve Mahrley, Joshua Tanner · Physics Education · 2012
In this paper we report on the use of two different light to frequency converters, four different light sources, three of which are novel and inexpensive, and a hand held digital multimeter with a frequency counter, suitable for making accurate and rapid determination of the optical inverse square law exponent of − 2 to better than ± 0.005 over more than a factor of 100 in distance and a factor of 5 × 10 5 variation of light intensity. Accurate data sets can be taken in 20–40 min, typically one minute per data point or less. The wide range of intensities measured makes a convincing demonstration of the optical inverse square law, and forms the basis for students learning how to plot log–log graphs over multiple orders of magnitude, extract power law exponents and learn about coefficients of determination. The extremely low cost of this high accuracy experiment and the ease of its implementation are appropriate for even the most modest budgets and least equipped high school physics laboratories.