# Re: Capacitance to free space

```Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net>

Hi Antonio,

> Original poster: "Antonio Carlos M. de Queiroz" <acmdq-at-uol-dot-com.br>
>
Capacitances are always
> directly
> proportional to the size, if the shape is kept.

Size being the area or linear dimension??  If I double the linear dimension
(proportions staying the same) of a toroid, will I 4x the cap or 2x the cap?
I bet you are right with size being a linear dimension.

Double the toroid linear dimension and the area increases 4x but the radius
of curvature also doubles and reduces the cap per unit area by 1/2.  Hence
capacitance only doubles.

Double the size of a flat plate capacitor, the area increases 4x, but the
separation between plates also doubles and halves the capacitance per unit
area. Hence the capacitance only doubles.

Gerry R

>
> For some capacitance formulas, see:
> http://www.coe.ufrj.br/~acmq/tesla/capcalc.pdf
>
> Antonio Carlos M. de Queiroz
>
>

```