Demostrador de AC-DC
This unique apparatus dramatically illustrates the differences between alternating and direct current. It consists of a permanent magnet mounted at the center of an evacuated bulb and within the loop of a long thin carbon filament. The bulb is mounted on a black bakelite box which provides either AC or DC current at the throw of a switch. In experiments, students are asked to determine which switch position corresponds to AC and which to DC. Well informed students will note that AC current causes the filament to oscillate at 60 cycles, while the DC filament maintains its field orientation and does not move at all. With instructions.