343
OF ENGINEERING FORMULÆ.
Electrical Formulae, by Paget Higgs, LL.D., C.E.—
continued.
compared with the resistance of the conductor of
the cable, the charge it will take will be directly
proportional to its length. If the resistance of the
battery is large compared with that ot the con-
ductor, the charge the cable will take will be
directly proportional to the square of its length.
When two or more cables whose farther ends are
to earth are charged so that the strengths of the
currents flowing through them are the same, the
charges will be directly proportional to the squares
of the lengths.
37. If dx = thickness of differential cylinder
at distance x from longitudinal axis of cable, its
resistance will be dr — -—-—and the whole
2 TT I x A
resistance of length I =
i ' R
1
2-n- IK J x 2ir lÅ
Å being the specific conductivity.
38. The resistance to the flow of electricity from
a central electrode of radius p to the periphery of
a regular polygon of n sides is
4
1 _
2irkS
log- --------------~
? 3 + cos. -
n >