Rank the value of `ointvec(B)vec(dl)` for the closed paths shown in figure from the smallest to largest.

Options

A. `a,b,c,d`
B. `a,c,d,B`
C. `a,d,c,b`
D. `a,c,b,d`

Answer

B

Explanation

We shall use `ointvec(B).dvec(I)=mu_(0)I` where `I` is the current encolsed by loop.
Net current enclose by path a is zero.
Net current enclosed by path `c` is `A`.
Net current enclosed by path `d` is `3A`.
Net current enclosed by path `b` is `5A`.