Geometric Optics is usually covered in introductory Physics, but apart from the details of how light reflects from a polished surface or bends as it goes from one medium to another, it's all geometry.[br][br]The purpose of this set of demonstrations is to convey the idea of an optical image. An image is where the object appears to be. In other words, your brain naively traces back the light that enters the eye as though it came in a straight line. If an object is placed at some position, light rays would appear to diverge from that point. However, if a lens (or other optical system) is placed in the path of the light, the rays can be bent to make them appear to diverge from some other place.[br][br]The demonstration is probably clearer than the above paragraph!

Click the boxes for the various demonstrations. Note that the first two appear to be the same and the second two appear to be the same...until the cloud is removed, that is.