Seeing invisible colours: An on-line inquiry-based activity on electromagnetic radiation

We created a formal inquiry-based activity on electromagnetic radiation for high school students. The main topics of the activity are the electromagnetic spectrum and the matter response to different wavelengths, with a focus on visible, UV, near, and far-infrared. The activity is linked to some informal learning aspects from the scientific theatre of the Milan University project "The Show of Physics". The activity can be done remotely, by maintaining an inquiry approach. In this work, we present the didactic path and the first results obtained.