A. Most radios have an internal AM antenna called a "loopstick". This consists of a ferrite rod with a coil of wire wrapped around it. Ferrite is a ceramic material with iron oxide and other compounds mixed in with it. This gives it a high magnetic permeability.
The frequencies at which broadcast AM radio operates have very long wavelengths, and the ferrite rod works well with them. You may have noticed that the radio picks up better when it is turned in one direction than another. This is because the loopstick is a directional antenna. It works best when either end of the rod is pointed at the station and works relatively poorly when it is turned side-on.