Q.A simple magnifying glass of focal length $5\ \text{cm}$ is used by a person whose near point is at $25\ \text{cm}$, with the image formed at the near point. Calculate the magnifying power of the lens.

A simple microscope (magnifying glass) is a single short-focal-length convex lens, used to view an object placed within its focal length so the lens forms a virtual, erect, magnified image. Magnifying power $M$, defined as the ratio of the angle the final image subtends at the eye to the angle the object itself would subtend viewed unaided from the near point, works out to $M=1+D/f$ when the virtual image is thrown to the near point $D$, or the slightly smaller $M=D/f$ when the object sits exactly at the focus so the (relaxe …