10:28in productionCh. 1 · The search/ 10:28 · ceiling 15 min
Physics · Engineering
Hans Christian Ørsted
Ørsted didn’t prove electromagnetism — he startled a compass, and changed physics forever.
Ørsted’s 1820 experiment showed that electric current deflects a compass needle — proving electricity and magnetism are linked. It established the circular geometry of magnetic fields around wires and launched electromagnetism as a unified science. But it offered no numbers, no field equations, and no mechanism — only observation, interpretation, and momentum.
A compass needle moved — not toward or away, but sideways — when current flowed.
4:29
The radiation mistake
He thought magnetism spread outward like light — a wrong analogy, but one that pointed to symmetry.
6:16
The circle
Three months after the first observation, he described the field as circular — the correct geometry.
Worth your time?
Yes. Study the whole thing.
4.5/ 5
What works
established electricity-magnetism linkage
identified circular field geometry
inspired immediate follow-up by Ampère and Faraday
What does not
quantitative measurement
field polarity
mathematical formulation
replication across conditions
Study it if
students of physics history
engineers tracing design lineage
teachers explaining field geometry
Skip it if
practising electromagnetics engineers
researchers seeking new field models
The written brief1 min read
What the work claims
An electric current produces a circular magnetic field around a wire, and magnetic effects radiate from all sides of that wire — establishing a direct, physical relationship between electricity and magnetism.
How it was done
Ørsted passed an electric current through a wire near a compass needle and observed its deflection from magnetic north. He had been seeking this connection since 1818 but was initially confused by inconsistent results.
What holds up
The deflection of a compass needle by a current-carrying wire is reproducible and foundational. The circular geometry of the magnetic field around the wire holds as a qualitative description confirmed by later work.
What does not
Ørsted did not measure field strength, directionality beyond circular geometry, or quantitative relationships between current and deflection. He did not identify polarity, nor did he distinguish between magnetic field lines and radiation analogies.
Why it matters beyond the lab
It ended the treatment of electricity and magnetism as separate phenomena. Without this observation, no electric motors, generators, or transformers would have been conceived on physical principles.
Is it worth your time
Yes — it is the first experimental demonstration that electricity and magnetism are linked, and it directly enabled Ampère, Faraday and Maxwell to build electromagnetism as a science.