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

LMT -1

10-1 " "

Electrical pressure........

Volt.

L3/2MT -2

108 " "

Energy.

Joule.

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 "