Sir, i'm nin from Malaysia. Can u explain the formation of mirage? it's quite confusing... And what is virtual object?? Here's a question : The Palomar Observatory Telescope has a parabolic mirror with a focal length of 80m.Calculate the magnification when a convex lens with a focal length of 5cm is used as the eyepiece. [ans:1600] how to do....? can ?? u explain? ??? ;D