Comments on the use of electromagnetic fields in biological studies.

For biological or cellular experiments using electromagnetic fields it is essential that the parameters defining the field be accurately specified if the results are to be meaningful and are to be compared with the same experiment conducted in a different laboratory. The interaction of living systems with electric and magnetic fields can come only through forces exerted on the charges on the system. If the charges are stationary the only origin of the force is the electric field. The electric field may be established by charge distributions, as in "capacitative plate" experiments, or by time-varying magnetic fields consists of a pair of coaxial coils each of equal radius and separated by a distance about equal to the radius. The electric field induced by a varying current in such a pair of coils varies both in space and in time. The field is always zero on the axis of symmetry, and increases to a maximum near the radius of the coils. The strength is proportional to the time-rat-of-change of the current in the coil, which depends not only on the amplitude and shape of the voltage pulse applied to the coil but also on the resistance and inductance of the coil. The purpose of this note is to describe how the important physical parameters may be determined.