Magnetic field at a distance r from an infinitely long straight conductor steady current varies as

Options

A. In the region `0lt r lt R`, the magnetic field is non-zero
B. In the region `Rltrlt2R`, the magnetic field is along the common axis
C. In the region `Rltrlt2R` the magnetic field is tangential to the circle of radius r, centered on the axis
D. In the region `rgt2R`, the magnetic field is non-zero

Answer

A, D

Explanation

In the region `0 lt r lt R B_(P)=0, B_(Q)!=0`, along the axis `:.B_("net")!=0`
In the region `Rltrlt2R B_(P)!=0`, tangential to the circle of radius r centered on the axis
`B_(q)!=0`, along the axis, `:.B_("net")!=0` neither in the directions mentioned in options (B) or (C).
In region, `rgt2R B_(P)!=0, B_(Q)!=0:.B_("net")!=0`