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ELECTROMAGNETIC SYSTEM 



Many of the magnetic quantities are analogues of certain electric quantities. 

 The dimensions of such quantities in the electromagnetic system differ from 

 those of the corresponding electrostatic quantities in the electrostatic system 

 only in the substitution of permeability //. for K. 



Conductance is the reciprocal of resistance, and the dimensional formula is 

 [L-7V 1 ]. 



Conductivity is the quantity of electricity transmitted per unit area per unit 

 potential gradient per unit of time. The dimensional formula is [M i L i fi' i / 

 L^M^T-^/QT] or [L^TfT 1 ]. 



Current, / (abampere-unit magnetic field, r—\ cm), flowing in circle, 

 radius r, creates magnetic field at its center, 2irl/r. Dimensional formula is 

 product of formulae for magnetic field intensity and length or [M*L*7 X " 1 /*"*]. 



Electric field intensity is the ratio of electric potential or electromotive 

 force and length. The dimensional formula is [M^OT" 1 ^]. 



Electric potential, or electromotive force (emf) ( ab volt-work = 1 erg), 

 as in the electrostatic system, is the ratio of work to quantity of electricity. 

 The dimensional formula is [M L 2 T~ 2 / M* D p*] or [M*UT 2 ^]. 



Electrostatic capacity is the ratio of quantity of electricity to difference of 

 potential. The dimensional formula is [L -1 ^ 2 /* -1 ]. 



Intensity of magnetization (/) of any portion of a magnetized body is 

 the ratio of the magnetic moment of that portion and its volume. The dimen- 

 sional formula is [A/'LTV'/L 3 ] or [Af*Z.-»rV]. 



Magnetic field strength, magnetic intensity or magnetizing force (/) 



is the ratio of the force on a magnetic pole placed at the point and the magnetic 

 pole strength. The dimensional formula is therefore the ratio of the formulae 

 for a force and magnetic quantity, or [MLT~ 2 /M i L^T' 1 fx i ] or [M i L"*r~ 1 /*~ i ] . 



Magnetic flux (<J>) characterizes the magnetized state of a magnetic circuit- 

 Through a surface enclosing a magnetic pole it is proportional to the magnetic 

 pole strength. The dimensional formula is that for magnetic pole strength. 



Magnetic induction (B) is the magnetic flux per unit of area taken per- 

 pendicular to the direction of the magnetic flux. The dimensional formula is 



[M J L?rV/^ 2 ] or [M*L-*rV]. 



Magnetic moment (M) is the product of the pole strength by the length of 

 the magnet. The dimensional formula is [M^L'T' 1 ^]. 



Magnetic pole strength or quantity of magnetism (m) has already 

 been shown to have the dimensional formula [M i L*T~ 1 n i ], 



Magnetic potential or magnetomotive force at a point is measured by 

 the work which is required to bring unit quantity of positive magnetism from 

 zero potential to the point. The dimensional formula is the ratio of the formulae 

 for work and magnetic quantity [ML^^/M^UT 1 ^] or [M i L i T~ 1 f i- i ]. 



Magnetic reluctance is the ratio of magnetic potential difference to mag- 

 netic flux. The dimensional formula is [L" 1 /*" 1 ]. 



SMITHSONIAN PHYSICAL TABLES 



