A circular conductor of radius ro=1cm has an internal field,
¯¯¯¯¯H=104ro(1a2sinaro−roacosaro)ˆaϕ(A/m)
where, a=π2r0
According to Ampere’s law,
Ienc=∮r=r0→H.dl
ro=10−2 m
∫2π0104r0(4r20π2sinπ2−2r20πcosπ2).r0dϕ
=104∫2π04r20π2dϕ
lenc=104.4r20π×2=8πAmpere