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

Answer

A,D

Explanation

`(A)` For `0 lt r lt R rArr B ne 0`
`(D)` For `r gt 2R rArr B ne 0`