The Three-Pole Electromagnet
A standard piece of demonstration apparatus in the second half of the 19th century was the horizontal electromagnet. Figure 1 shows a pair of them from the 1860 era in my personal museum. The coils were wound on mandrels about 7 mm in diameter, which were then removed after the turns were glued together. With no core, or a brass rod as a core, it will support only a few ferrous objects from each end. With a ferrous metal core, strands of small iron objects (washers or paper clips) can be supported. It is hard to imagine how amazing this demonstration must have been to students when they first saw it in the 1840s. Perhaps our students today can recreate this amazement when given a single-turn, hollow-core solenoid, an iron rod that can fit into the core, a power supply, and a supply of paper clips—with no prior hints as to what will happen.
“The Three-Pole Electromagnet”, The Physics Teacher, 49, 496 (2011)
The Physics Teacher