So far we have discussed self-and mutual inductances in static terms. Because inductances depend on the geometrical shape and the physical arrangement of the conductors constituting the circuits, and, for a linear medium, are independent of the currents, we were not concerned with nonsteady currents in the defining of inductances. However, we know that resistanceless inductors appear as short-circuits to steady (d-c) currents; it is obviously necessary that we consider alternating currents when the effects of inductances on circuit and magnetic fields are of interest. A general consideration of time-varying electromagnetic fields will be deferred until the next chapter. For now we assume quasi-static conditions, which imply that the currents vary very slowly in time and that the dimensions of the circuits are very small in comparison to the wavelength. These conditions are tantamount to ignoring retardation and radiation effects, as we shall see when electromagnetic waves are discussed in chapter 8.