Faraday : créer de l'électricité avec le magnétisme ?
The Discovery of Electromagnetism
Early Discoveries in Electromagnetism
- In 1820, Danish physicist Hans Christian Ørsted discovered that an electric current creates a magnetic field around it, demonstrating the relationship between electricity and magnetism.
- André-Marie Ampère later showed that a fixed coil could induce a current in another circuit, observing this phenomenon in 1822 with a simple copper ring parallel to the coil.
Attempts at Inducing Current
- Michael Faraday reported several attempts from 1824 onwards to induce an electric current using either another current or a magnet, but these efforts initially yielded no results.
- In 1831, Dutch physicist Willem Einthoven highlighted the extraordinary power of electromagnets constructed by Joseph Henry, which could lift heavy loads despite being powered by modest batteries.
Faraday's Breakthrough Experiment
- Faraday utilized multiple turns (spires) in his coils to significantly enhance the magnetic effect during his experiments aimed at inducing currents.
- He successfully demonstrated induced current through two coils wrapped around an iron ring; when he established or cut off the current in one coil, it caused noticeable deflections on a galvanometer connected to the second coil.
Observations and Variations
- When cutting off the first coil's current, Faraday noted that the induced current flowed in the opposite direction.
- He experimented further by placing both coils around a wooden cylinder instead of iron and observed minimal effects unless they were closely positioned.
Understanding Induction Effects
- By adjusting distances between coils and utilizing switches for control, Faraday found transient deflections on the galvanometer indicating induced currents.
- The introduction of an iron core significantly increased galvanometer readings compared to setups without it.
Exploring Magnetic Influence
- Faraday discovered that when establishing current in one coil, the induced current was always opposite to that of its source.
- He explored various methods of changing magnetic fields within coils and found that moving magnets or rotating coils could generate alternating currents.
Legacy of Electromagnetic Induction