Page:Electricity (1912) Kapp.djvu/69

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ON POTENTIAL
65

where is the potential in dyne-centimetres, the charge on the sphere in electrostatic units, and the distance of the point from the centre of the sphere in centimetres at which the approaching motion has terminated.

The reader should note that the conception of a person actually carrying a body containing unit charge in his hand, and approaching it to the sphere, is merely introduced as illustrating a mathematical relation between certain quantities, and must in no ways be taken literally. The formula only says that the potential is an attribute of the particular point in space distant cm. from the centre of the active mass . In another point, distant cm., the potential will have a different value, say If is nearer to the active centre than , then will be greater than , and we may therefore speak of a potential difference existing between the points and . Or in symbols

Since is smaller than , the potential difference is positive. We must expend energy in bringing the unit positive charge, and in fact any positive charge, from to .