Describe I-shaped electromagnet.

The figure given below shows a long copper wire wound on $\mathrm{U}$-shaped soft iron core. Name this arrangement. If a steady current is passed in the wire as shown, mark the north and south poles on the iron core.

The figure below shows two loops of radii $r$ and $\raisebox{1ex}{$r$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$ and having number of turns $n$ and $2n$ respectively. Calculate the ratio of magnetic field induced in the two loops when same current is passed in these loops.