Note on a common virtual image Available to Purchase

An observer above the plane surface of a liquid of index of refraction n, looking at a point object which is a distance Y below the surface, will see a virtual image of the object. For light rays which emerge in air at an angle of refraction θ₂=0, the virtual image will be at a distance (Y/n) below the surface. The case where θ₂≠0 is rarely discussed in texts. As a result, students may be left with the impression that the location of the virtual image is independent of θ₂. The virtual image is astigmatic and the locations of the different components of the astigmatic image depend on the angle of refraction θ₂. The location of the various components of the astigmatic image are derived; a laboratory experiment to measure the locations of the components is described. The results of the measurements are in good agreement with the theory.