2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/166025The Casimir energy is computed in the geometry of interest for the most precise experiments, a plane and a sphere in electromagnetic vacuum. The scattering formula is developed on adapted plane-waves and multipole basis, leading to an expression valid for arbitrary relative values of the sphere radius and inter-plate distance. In the limiting case of perfect reflection, the electromagnetic result is found to depart from the commonly used proximity-force approximation (PFA) significantly more rapidly than expected from scalar computations.4 pages, 3 figures. A comparison with existing results (new reference [26]) was addedQuantum Physicstext