Tables of physical and chemical constants and some mathematical functions / by G.W.C. Kaye and T.H. Laby.

  • Kaye, G. W. C. (George William Clarkson), 1880-1941.
Date:
[1941]
Catalogue details

Licence: Public Domain Mark

Credit: Tables of physical and chemical constants and some mathematical functions / by G.W.C. Kaye and T.H. Laby. Source: Wellcome Collection.

    24/200 (page 12)
    The dimensions of electric held, E, potential, Y, e.m.f.. <*’, disp'aeement, D, polariza¬ tion. P, dielectric constant, e, capacity, C, are derived from those of Q using the relations in the table on electrostatic quantities. To calculate the dimensions of magnetic quantities. Ampere's law for the magnetic held of an electric current is used. The work done on a magnetic pole, m, when taken round a path which encloses a current, l. is proportional to I and to tn, but is independent of the path. Ampere’s law may be expressed : \\ = 47tI/;z/A, where 4- A is the constant of proportionality. All the systems of units in use put A = 1 and give to Im the dimensions of work : to do this is a convention, but so far it is a generally accepted one. i^See “ Giorgi units. p. 13d The dimensions of I are [QT-1], and we get for those of [«/] = [M‘L*t-»] The dimensions of the other magnetic quantities are derived from those of magnetic pole, using the defining relations in the table containing those, quantities. Dimensions of E.M. Units are derived in a similar manner, starting with the inverse square law for magnetic poles. Ratio of E.M. and E.S. Units:—The ratio of the e m u. of charge to the e.s.u. is c. where c is the measure of the velocity of light in cm. sec.-1 Now the dimensions of charge must be the same on all systems of units. If we equate the dimensions of the c.s. to those of the e.m. unit it is found that [/*-**-*] = [L/T], that is 1 \ /<€ has the dimensions of a velocity. This is necessary if the dimensions which have been derived are to be consistent with Maxwell’s electromagnetic theory in which .* = 1 \ /i0trt is the expression for the velocity of light in a vacuum. If the A mentioned above is not of zero dimensions then V: A. The dimensions of the e.m. and e.s. units are tabulated below. ELECTRICAL AND MAGNETIC UMTS c. the ratio of the electromagnetic to the electrostatic unit of quantity, is usually taken as 3 \ io10, and is a pure number (p. 84). (See Rucker, Phil. Mag., 22, 1SS0.) Reference: “International Conference on Physics. London, 1034: Reports on Units. Unit. Electrical Charge . Resistance Current . Potential. E.M.F. . Electric field Conductivity Capacity. Inductance . Displacement Polarization . Dielectric con- ( stant . . . ! Dimensions. Sym¬ bol. E S. Unit. E.M. Unit. E.S.U. L. M. T. e. L. M. T. /*.; E.M.U Eels dons. Units. —.1- Q R I V <*' E K c I i i o a t * £ I I £ £ o o I o L ; M i — i o D P -£ £ 4 £ -1 £ 1 -1 -2 £ -1 -£ -1 -£ -1 -£ -1 1 o 1 2 -1 -1 £ -1 I 000 1 £ £ o-l 1 o -1 1 £ | -1 -£ | £ -2 £ H-i 1 4 i -a 4 -20 1-1 -10 2 -I I O r*ae. coulomb ohm ampere rolt 1 jc 4 r- ;!. c j (volt cm,) 1 IP ' .3 ' -I £ o -£ -I £ o -£j -20 2 - 1 c 1 /<* 1 i'c i/<3 ohm-1 farad t henry l\ F.M.U >=io-1 — IO* = io-1 = IOs J—IO“ = 10* i cm. 1 1 E.S.U. 3 x 10s* 4x IO-11 :3 x10s* : 1/300 : 9 X IO11 :QX IO11 £XIO”11 4 X IO-20 3 x io10. ■ 3X io10