Our knowledge of electromagnets developed from a series of observations. In 1820, Hans Oersted discovered that a current-carrying wire produced a magnetic field. Later in the same year, André-Marie Ampere discovered that a coil of wire acted like a permanent magnet and François Arago found that an iron bar could be magnetized by putting it inside of a coil of current-carrying wire. Finally, William Sturgeon found that leaving the iron bar inside the coil greatly increased the magnetic field.
Mark is doing an experiment creating a magnet. He takes a piece of iron named iron bar A and wraps it in a coil of copper wire. After that he puts an electric current through the copper for about an hour.
Based on the above, answer the following question:
Given Mark repeates his experiment with a second iron bar, Iron bar B but leaves it in the coil for 3 hours, which bar has a stronger magnetic field, Iron bar A or Iron bar B?