Question

Which lens has a virtual focus?

Answer 1

Focus

When a parallel beam of light falls on a lens they get refracted. The refracted rays from a lens the rays converge or appear to converge at a point that is called as principal focus or focus of the lens. In a broad view, lenses are of two types, convex and concave. In the case of a convex lens refracted rays actually pass through the focus and appear to pass through in the case of a concave lens.

1. The actual converging point is called real focus and when it diverged rays are extended back they appear to emerge from a point that is called the virtual focus.
2. Real focus is obtained in the case of a convex lens and virtual focus is obtained in the case of a concave lens.

A concave lens has a virtual focus because the rays diverge outside and seems to meet virtually at focus.