A double convex glass lens of focal length f and having a circular aperture is cut into two halves, each having a semicircular aperture. The focal length of each half is

When a convex lens is cut into two halves along the principal axis, each half maintains the same curvature of surfaces as the original lens. Since focal length depends on the radii of curvature of the lens surfaces and the refractive index, and these properties remain unchanged, the focal length of each half remains the same as the original lens (f). The aperture size reduces but does not affect focal length.