In the diagram shown, a wire carriers current `I`. The loop has `N` turns and part of helical loop on which arrows are drawn is outside the plane of paper. What is the value of the `oint vecB.vec(dl)` (as in Ampere's law) on the helical loop shown in the figure?

Options

A. `-mu_(0)(NI)`
B. `mu_(0)(I)`
C. `mu_(0)(NI)`
D. Zero

Answer

C

Explanation

Here, `vec(B)` (due to I) and `dvecl` will be same direction. So, `oint vec(B). vec(dl)=ointBdl cos0^(@)`
`ointBdl=Bointdl=BN2pir=N(B3pir)=Nmu_(0)I`