Labs for the sake of it
Almost every practical I do with my class is assessable according to IB criteria. There are several reasons for this, one is that the criteria fit well with the type of experiments we do in physics. Change one thing - measure another - linearise an equation - plot a straight line - analyse the graph. Another reason is because other teachers in workshops etc. are often asking for new ideas for assessable practicals and I have to try them out on somebody. However there are some great experiments that don't really fit into the criteria. I have 2 Pasco single slit diffraction set ups. They comprise of an optical bench, LASER, high sensitivity light sensor, rotational motion sensor with linear translator and an interface. The problem is there are only 4 different width single slits, so plotting a straight line graph is going to be problematic. Anyway today some of my students who have already completed enough DCP practicals did it anyway, it's a really neat and really expensive experiment that nicely shows the relationship between the spots of light and the intensity graph, as well as the effect of changing the slit size on the width of the central maxima. During the lesson one student asked me how it can be that when he made the slit smaller, the central maxima got narrower. It can't and it didn't.