Draw a neat diagram of electric bell and describe its working.

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. 

In the given figure what is the direction of the force on the current-carrying conductor?