Question

the ratio of electric potentials at the point e to that at the point f is

Answer 1

Point charges, such as electrons, are among the fundamental building blocks of matter. Furthermore, spherical charge distributions (like on a metal sphere) create external electric fields exactly like a point charge. The electric potential due to a point charge is, thus, a case we need to consider. Using calculus to find the work needed to move a test charge q from a large distance away to a distance of r from a point charge Q, and noting the connection between work and potential \left(W=\phantom{\rule{0.25em}{0ex}}-q\Delta V\right)