How a Compass Needle Changed the World
The odd little event that launched the electromagnetic revolution
Few people end up giving lectures in the physical sciences at a major university. Rarer still are people who make important scientific discoveries. Hans Christian Ørsted may have the unique distinction of making a world-changing scientific discovery while giving a university lecture.
On April 21, 1820, Ørsted was conducting a classroom demonstration at the University of Copenhagen. While passing an electric current through a wire, Ørsted noticed that every time the current was switched on or off, a nearby compass needle would move slightly.
Magnetism and electricity were both familiar physical forces at the time. However, this was the first time anyone had noticed a connection between the two.
The effect intrigued Ørsted. Without mentioning anything to his students, he made a mental note to come back and experiment more in his private time. Over the next three months, he reproduced this odd behavior under a variety of conditions. He noticed and recorded some interesting observations:
- The needle moved through a larger angle when a stronger electric current flowed through the wire.
- The needle also moved more when the wire and needle were placed…
