1. electrometer, absolute An electrometer designed to give directly the value of a charge in absolute units. In one form a plate, a b, of conducting surface is supported or poised horizontally below a second larger plate C, also of conducting surface. The poised plate is surrounded by a detached guard ring--an annular or perforated plate, r g r' g'--exactly level and even with it as regards the uppersurface. The inner plate is carried by a delicate balance. In use it is connected to one of the conductors and the lowerplate to earth or to the other. The attraction between them is determined by weighing. By calculation the results can be made absolute, as they depend on actual size of the plates and their distance, outside of the potentialdifference of which of coursenothing can be said. If S is the area of the disc, d the distance of the plates, V-V1 the difference of their potential, which is to be measured, and F the force required to balance their attraction, we have:
F = ( ( V - V1 )^2 * S ) / ( 8 * PI * d^2 )
If V = 0 this reduces to
F = ( V^2 * S ) / ( 8 * PI * d^2 ) (2) or V = d * SquareRoot( (8 * PI * F ) / S ) (3)
As F is expressed as a weight, and S and a as measures of area and length, this gives a means of directly obtaining potentialvalues in absolutemeasure. (See Idiostatic Method--Heterostatic Method.)
Definitions of electrometer, absolute
