Find the values of `ointvecB.vec(dl)` for the loops `L_1, L_2 and L_3` in Fig. (The sense of `vec(dl)` is mentioned in the figure)

Explanation

For `L_(1)oint vecB.vec(dl)=mu_(0)(I_(1)-I_(2))`
here `i`is taken positive because magnetic lines of force produced by `I_(1)` is anti clockwise is seen from top. `I_(2)` produces lines of `vecB` in clockwise sense as seen from top. The sense of `vec(dl)` is anticlockwise as seen from top.
for `L_(2):ointvecB.vec(dl)=mu_(0)(l_(1)-l_(2)+l_(4))`
for `L_(3):oint vecB.vec(dl) =0`