Which 1820 experiment showed that a current-carrying wire can deflect a compass needle?

Ørsted’s experiment showed in 1820 that a current-carrying wire can deflect a compass needle.

Danish physicist Hans Christian Ørsted noticed that a compass needle moved when an electric current flowed through a nearby wire. The deflection demonstrated a direct connection between electricity and magnetism, which had previously been treated largely as separate subjects.

The effect depends on the relative position of the wire, compass, and current direction. Reversing the current reverses the needle’s deflection. The discovery quickly encouraged André-Marie Ampère and other researchers to investigate forces between currents and the magnetic fields they produce.

The experiment is historically important because it introduced the idea that electric current generates a magnetic field. It is not the same as electromagnetic induction, in which a changing magnetic environment produces an induced voltage or current.