The birth and life of an electromagnet

In September 1820, the French physicist D. Arago noticed that the wire through which current flows attracts iron filings and magnetizes steel needles like a magnet. A. M. Amper once entered the laboratory of D. Arago and proposed to roll the wire into a spiral, and place the needle inside the spiral. Scientists saw that the needle was magnetized much stronger than before. The resulting spiral or tube was subsequently called a solenoid. Having caught the connection between the magnet and the solenoid, Ampere suggested that inside the magnet there are a huge number of tiny rings with current. Ampere’s idea was true - only the role of rings with current, as we now know, is played by electrons orbiting around atomic nuclei. The birth of an electromagnet was approaching...

The birth of an electromagnet was approaching...

Ampere's solenoid was not yet an electromagnet - it lacked an iron core, which became a real magnet when passing current through turns of wire. The core enhanced the action of the solenoid many times, making the electromagnet much stronger than the best natural magnets. And this core was first introduced into the solenoid by the English mechanic William Sturgeon (1783-1850). In 1825, Sturgeon presented to the Art Society the first electromagnet he built.

It was a horseshoe-shaped rod coated with varnish, 30 cm long and 1,3 cm in diameter. Only one layer of bare copper wire was wound on this rod, which was closed to an electric battery. With a mass of 0,2 kg, Sturgeon's electromagnet lifted an iron load, almost 20 times heavier.

Until 1840, Sturgeon's electromagnets were the strongest in the world. And then the future great physicist D. Joule came forward. He increased the number of poles of the electromagnet and rationally placed them on the load. At the same time, the Joule electromagnet was capable of lifting 1,2 tons with its own weight of 5,5 kg! It was important that the poles were paired and their number even. It turned out that not every increase in the number of poles is beneficial. So, for example, the "three-armed" electromagnet is worse than the usual bipolar, because the magnetism of each of the rods interferes with the others. It is also disadvantageous to make one large electromagnet from separately wound small electromagnets.

Electromagnets have become widely used in industry for lifting heavy steel loads. In 1864, an electromagnet weighing 260 kg was built in New York.

But, the electromagnet was not such a safe lifting device. As soon as the current stopped, the electromagnet instantly lost power, and a terrible load fell on what and anyone. Therefore, in the future they began to act differently.

The turns of wire for the electromagnet began to be wound not on simple iron, but on the magnetized material - a permanent magnet, and so that when passing current, demagnetize it. To lift the load, the current was turned off, and a permanent magnet (and now there are very strong permanent magnets) attracted steel, iron and cast-iron objects, which they lifted and carried into place. And in order to release the load, current was supplied to the turns, and the magnet was temporarily demagnetized - the poles of the permanent magnet and the solenoid windings were opposite! The load disengaged. When the magnet did not have to work, the current, of course, was turned off, moving the magnet away from iron objects away, for example, lifting it into the air.

In the first half of the XX century. Electromagnets were built that lifted weights up to 75 tons. However, it turned out that the benefit from Sturgen's introduction of an iron rod inside the winding gradually began to disappear. While the coils were small, iron greatly increased the magnet's lift. But then, the creators of electromagnets noticed that with an increase in the strength of the magnet, its iron seemed to be saturated and no longer helps the electromagnet. They began to build magnets with short sharpened poles, a massive yoke and huge coils. You can, of course, make the amount of iron in an electromagnet so large as not to bring it to "oversaturation". The American inventor Edison, for example, proposed building the largest electromagnet in the world by wrapping magnetic iron ore rock in the American city of Ogden, weighing more than 100 million tons!

Unfortunately, this bold and witty project was not implemented.