3. Experiment 1: reflection and refraction of light incident on a glass block The aim in this experiment is to explore the basic laws of reflection and refraction at a planarair–glass interface. Referring to figure 1 this entails measuring the angles of reflection θr and refraction θt as a function of angle of incidence θi. Provided the glass block is aligned correctly, the angle of incidence θi can be read directly from the protractor. Likewise, if the white screen is adjusted so that reflected ray falls on the reference line marked on it, the angle of reflection θr can be read off from the protractor. As set up in figure 1, determination of the angle of refraction requires measurement of l and y: θt = tan−1(y/l).