In scattering problems, it is desirable to determine an unknown scattered field E s that is due to a known incident field E i . Unfortunately, the EFIE relates the scattered field to J, not the incident field, so we do not know what J is. This sort of problem can be solved by imposing the boundary conditions on the incident and scattered field, allowing one to write the EFIE in terms of E i and J alone. Once this has been done, the integral equation can then be solved by a numerical technique appropriate to integral equations such as the method of moments.