Allows Additional Learning Through Interactivity

As students interact with the Physlet they get constant, real-time, feedback which can help them to learn.  For example, suppose a student thinks of focal point as "the place where all rays converge" and knows that it is supposed to be a constant value.  As they move the source of light the place where all rays converge changes.  The contrary feedback from the Physlet will help them confront their misunderstanding