Using a photo‐resistor to verify irradiance inverse square and Malus' laws

In this article we present two single teaching experiments both related to light intensity measurements. These simple experiments can be conducted in order to train and teach other concepts and capabilities far exceeding those most obviously involved. The main problem presented to the students is that concerning the light detector. Our experiment uses an inexpensive, find to easy and trustable one, a photo‐resistor. The student has to use some well suited method in order to calibrate the photo‐resistor for intensities. We explore two methods to achieve this calibration, one very simple and with inexpensive materials and other with more expensive equipment. Afterwards, students proceed studying the behavior of the intensity of a point source with distance in order to verify the inverse square law, as well as the behavior of light intensity with the angle between the transmission axis of two linear polarizers, in order to verify the Malus' Law. Both experiments explore data treatment and graphics in order t...