5.1.Given the current density J = −10 4 [sin(2 x )e −2 y a x +cos(2 x )e −2 y a y ]kA /m 2 :
J =400 sin ?
r 2 +4 a r A /m 2
?2 +0 .01 a z A /m 2
5.7.Assuming that there is no transformation of mass to energy or vice-versa,it is possible to
write a continuity equation for mass.
5.9a.Using data tabulated in Appendix C,calculate the required diameter for a 2-m long nichrome
wire that will dissipate an average power of 450 W when 120 V rms at 60 Hz is applied to it:
5.11.Two perfectly-conducting cylindrical surfaces are located at ?=3 and ?=5 cm.The total
current passing radially outward through the medium between the cylinders is 3 A dc.Assume
the cylinders are both of length l .
a)Find the voltage and resistance between the cylinders,and E in the region between the
cylinders,if a conducting material having ?=0 .05 S /m is present for 3 <?5 cm:
Given the current,and knowing that it is radially-directed,we ﬁnd the current density
by dividing it by the area of a cylinder of radius ?and length l :