Question

History of spherical mirrors and human civilisation

Answer 1

Parabolic mirrors were also described by the Physicist Ibn Sahl in the 10th century& Ibn al Haytham discussed concave & convex mirrors in both cylindrical and spherical geometries,carried out a number of experiments with mirrors& solved the problem.In the ancient time dark water collected was considered or used as mirrors by people.Due change in the environment there was an introduction of obsidian mirrors and then followed by metal coated glass mirrors which led to discovery of metal coated spherical or parabolic mirrors. Spherical mirrors have the shape of piece cut out of a spherical surface.There are two types of spherical mirrors  that is concave & convex.Ptolemy also carried out experiments with curved polished iron mirrors & discussed about convex spherical mirrors in his book optics.Although finding a focal length of spherical mirror was a tough task but finally Ibn al Hy tham got a break through by finding out the focal length of curved surfaces using the laws of reflection.