What invention did Edison create to demonstrate the dangers of alternating current?

Edison's invention of the electric chair was a notable and critical moment in the history of electrical systems, particularly in the context of the battle between alternating current (AC) and direct current (DC). He created the electric chair as part of a campaign to demonstrate the dangers associated with alternating current, which was being promoted by his rival, Nikola Tesla, and George Westinghouse.

By using the electric chair in public demonstrations, Edison aimed to show that AC was more dangerous than his own preferred direct current. The electric chair was designed to administer a lethal shock using alternating current, which helped cement the perception that AC was hazardous. This aggressive campaign against AC played a significant role during the period known as the "War of Currents," where Edison's advocacy for DC contrasted sharply with the growing popularity and eventual dominance of AC in the electrical industry.

The other options, like the light bulb, while significant in Edison's career, do not directly relate to the issue of demonstrating the dangers of alternating current. The light bulb was a groundbreaking invention in its own right but was intended to showcase the benefits of electric light rather than to confront the risks of AC. Similarly, the electric fence and the telegraph, while relevant to electrical innovation, did not