Edge Corrections for Strip and Disc Capacitors

We present a precise numerical method for calculating the edge correction for a long rectangular plate capacitor, and compare the results with available approximate formulas. We give numerical results for the disc capacitor which are much more accurate than the approximate formulas at low capacitances (a/h <100, where a = radius and h = separation). These results match or surpass the precision of present-day capacitance bridges. We discuss the difficulties encountered in attempting to extend the work to larger a/h ratios.