  Using the Finite-Difference-Time-Domain (FDTD) method, we compute the
electromagnetic field distribution in and around dielectric media of various
shapes and optical properties. With the aid of the constitutive relations, we
proceed to compute the bound charge and bound current densities, then employ
the Lorentz law of force to determine the distribution of force-density within
the regions of interest. For a few simple cases where analytical solutions
exist, these solutions are found to be in complete agreement with our numerical
results. We also analyze the distribution of fields and forces in more complex
systems, and discuss the relevance of our findings to experimental
observations. In particular, we demonstrate the single-beam trapping of a
dielectric micro-sphere immersed in a liquid under conditions that are typical
of optical tweezers.
