P27_006.PDF

6. We express the magnitude of the current density vector in SI units by converting the diameter values

in mils to inches (by dividing by 1000) and then converting to meters (by multiplying by 0 . 0254) and

ﬁnally using

A =

πR 2 =

4 i

πD 2

J =

10 6 A/m 2 . In fact, this is the wire with the largest value of J allowed by the given

data. The values of J in SI units are plotted below as a function of their diameters in mils.

7e+06

6e+06

5e+06

4e+06

40 60 80 100 120 140 160 180 200

D(mils)

For example, the gauge 14 wire with D =64mil=0 . 0016 m is found to have a (maximum safe) current

density of J =7 . 2