The Electro-Magnetic System Of Electric Units
Description
This section is from the book "Scientific American Reference Book. A Manual for the Office, Household and Shop", by Albert A. Hopkins, A. Russell Bond. Also available from Amazon: Scientific American Reference Book.
The Electro-Magnetic System Of Electric Units
Unit Of Current
That current which, flowing in a conductor 1 centimeter long, and of 1 centimeter radius, produces at the center of the arc a magnetic field of unit strength.
This unit is ten times the ampere.
Unit Of Potential
Unit difference of potential exists between the ends of a conductor, when the expenditure of 1 erg per second will cause unit current to flow.
This E.M.F. is equal to one hundred-millionth of a volt.
Note
The erg = work done by a force of 1 dyne through a distance of one centimeter = 0.001019 gramme - cent = 0.00000007386 foot-lb. (London).
Unit of Resistance is that resistance which requires unit difference of potential to cause unit current to flow.
This resistance is 1,000-millionth of an ohm.
For ready reference the units most frequently used in practice are tabulated below, together with their value in C.G.S. absolute units.
Electrical Quantity. | Name of Unit. | Dimensions of Unit. | Value in C.G.S. Units. |
Resistance | Ohm | LT -1 | 109 C.G.S. units. |
Current | Ampere | L½M½T -1 | 10-1 " " |
Electrical pressure........ | Volt. | L3/2M½T -2 | 108 " " |
Energy. | L2MT -2 | 107 " " | |
Capacity | Farad | L-1T2 | 10-9 " " |
Capacity | Microfarad | 10-15 " " | |
Power | Watt | L2MT -3 | 107 " " |
Power | Kilowatt. | 1010 " " | |
Work. | Watt-hour | 109X36 " | |
Work. | Kilowatt-hour | 1012X36 " |
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