The power of plane mirror is ____
Two lenses having powers +2D and -4D respectively are put together. Power of the combination would be
Two lenses with powers; 2D & -4D are kept together. What is the effective focal length of the combination?
A symmetric double convex lens is cut in two equal parts by a plane perpendicular to the principal axis. If the power of the original lens was 4D, the power of a cut-lens will be