From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Comparison of a concentric sphere gap, including formulas for electric force and potential difference.
| Identifier | ExFiles\Box 54\3\ Scan236 | |
| Date | 17th July 1924 guessed | |
| -5- COMPARISON OF CONCENTRIC SPHERE GAP WITH ABOVE. If the gap be a concentric sphere gap, instead of a concentric cylindrical gap (though this is not so practical a case), it is interesting to note that the electric force in this instance at radius r between a and b is V a b / (b-a)r^2 which at the inner radius a is V b / a (b-a) The same reasoning as in the case of a cylindrical gap again applies and for a variation of a (b constant) the minimum electric force at the surface of the wire for a given potential difference V occurs when a = b/2 and is 2V/a or 4V/b Further for a given outer radius b and a given bearable electric stress E, the maximum potential difference withstandable by the gap is Eb/4, occurring when the central wire is of radius b/2. EFC. | ||