The figure shows a part of a complete circuit. At the instant shown, the current `i=2A` and it is decreasing at rate `2xx10^(3)A//s`. Find the potential difference between A and B and energy stored in the magnetic field at this instant. `V_(A)-12+3i+15+5i+L(di)/(dt)+2i=V_(B)`

Explanation

By KVL, `V_(A)-12+3i+15+5i+L(di)/(dt)+2i=V_(B)`
`"or "V_(A)-12+3(2)+15+5(2)+(1xx10^(-3))(-2xx10^(+3))+2(2)=V_(B)`
`therefore" "V_(A)-12+6+15+10-2+4=V_(B)`
`V_(A)+21=V_(B)`
`rArr" "V_(A)-V_(B)=-21V`.
Energy stored `U=(1)/(2)Li^(2)=(1)/(2)xx10^(-3)xx4=2mJ.`