This sub-unit analyses the transfer of energy due to radiation and explores thermal radiation. In dependence of classroom curriculum, the development of activities here described needs a recall or introduction of the main concepts connected with electromagnetic radiation. The deepening level of such introduction is dependent from the knowledge level of the classroom as well as from previous students’ curriculum. Usually pupils are more familiar with heat transfer by conduction because of their experiences of everyday-life phenomena. The physical concept of energy propagation by radiation is introduced to the class usually by reporting the example of the light radiation travelling from the Sun to the Earth across the empty space, without any support from conduction and convection, which both need a medium. This example, even if quite convincing, is not strong enough to persist into the student imagery of energy propagation, probably because of the absence of any practical activity which can help the class to directly experience the transfer of energy by radiation. The following experimental activities are proposed as an inquiry based learning path aimed at the practical exploration of energy transmission by thermal radiation. The main concepts to recall can be synthesised as follows.Radiation is the common name for electromagnetic energy travelling through space. It can travel very fast (the light speed c = 2.998 x 108 m/s), also through the vacuum. It doesn’t need material to travel in. It has many forms, including visible light, infrared (IR), ultraviolet (UV), X-rays, microwaves, and radio waves. These are all the same form of energy, just with different frequencies and amounts of energy.
Different frequencies of radiation interact with matter differently and this fact makes them seem more different to us than they really are. In many everyday situations we observe bodies heated by radiation gaining thermal energy, which is mostly transferred by infrared (IR) and visible radiation.During the development of the subunits, new instruments will be analysed: the infrared thermometers and cameras.The starting point is the analysis of Activity 1.3 of sub-Unit 1 that pointed out that light can warm the walls of our house models and this warming effect is increased if the wall colour is dark or black.The first problem to face is that to better measure the heating effects of radiation by constructing a simple “radiometer” (see Activity 4.1).Activity 4.2 will measure the heating effect of sun radiation on bodies of different colours. Activities 4.3 will show that our radiometers are able to make evident a radiation different than the visible one and introduce the IR radiation.One of the last two activities can be chosen by the teacher according to the level of the classroom.Activity 4.4 will propose an open inquiry approach to the analysis of IR apparatuses (video, images, thermometers,….)Activity 4.5 proposes a video were the same experiment is performed in presence and absence of atmospheric air in order to deepen the knowledge of IR radiation.The following table characterises the activities from the point of view of the required type of inquiry and considering 5E model of the Learning Cycle.
