1)

The current density varies with radial distance r as J = ar2, in the cylindrical wire of radius R.The current passing through the wire between radial distance R/3 and R/2 is 


A) 65πaR42592

B) 25πaR472

C) 65πa2R32938

D) 81πa2R4144

Answer:

Option A

Explanation:

Given , J= a r2

i=21J×2πrdr=R/2R/3ar2×2πrdr

    =2πaR/2R/3r3dr=2πa|r44|R/2R/3

=πa2[(R2)4(R3)4]

  =πaR42×6581×1665πaR42592