A magnetic pole of strength 1Am is moved 10 times around a long straight wire carrying a steady current of $\pi$A. The work done is (assume ${\pi }^2\approx 10$)
 

work done to make one unit north pole once around the conduction is ${\mu }_{0}i$ joules ( Ampere's circuital law )

 for ten rotations 10${\mu }_{0}i$ joules

$W=10\times 4\pi \times {10}^{-7}\times \pi =4{\pi }^2\times {10}^{-6}= 40\mu J \left(\because {\pi }^2\approx 10\right)$