A steady current `I` flows along an infinitely long hollow cylindrical conductor of radius `R`. This cylinder is placed coaxially inside an infinite solenoid of radius `2 R`. The solenoid has a `n` turns per unit length and carries a steady current `I`. Consider a point `p` at a distance `r` from the common axis . The correct statement(s) is (are)

Options

A. In the region `0 lt r lt R`, the magnetic field is non - zero
B. In the region `R ltr lt 2R`, the magnetic field is along the common axis
C. In the region `Rlt r lt 2R`, the magnetic field is tangential to the circle of radius `r`, centered on the axis
D. In the region `r gt 2R`, the magnetic field is non - zero

Answer

A, D

Explanation

In the region ` O lt r lt R, the magnetic field is present due to current in solenoid.
In the region ` r gt 2R`, the magnetic field is present due to the current in the cylinder.
For the region ` R lt r lt 2R`, the magnetic field is neither along the common axis , nor tangential to the circle of radius `r`. ` (a) and (d)` are correct
options.