Magnetism | Can’t Sleep? Discover the Power of Attraction

Benjamin Boster (0:01)

Welcome to the I Can't Sleep Podcast, where I help you drift off one fact at a time. I'm your host, Benjamin Boster, and today's episode is about magnetism.

Magnetism is the class of physical attributes that occurs through a magnetic field, which allows objects to attract or repel each other. Because both electric currents and magnetic moments of elementary particles give rise to a magnetic field, magnetism is one of two aspects of electromagnetism. The familiar effects occurring in ferromagnetic materials, which are strongly attracted magnetic fields, and can be magnetized to become permanent magnets, producing magnetic fields themselves. Demagnetizing a magnet is also possible. Only a few substances are ferromagnetic. The most common ones are iron, cobalt, nickel, and their alloys. All substances exhibit some type of magnetism. Magnetic materials are classified according to their bulk susceptibility. Ferromagnetism is responsible for most of the effects of magnetism encountered in everyday life. But, there are actually several types of magnetism. Paramagnetic substances, such as aluminum and oxygen, are weakly attracted to an applied magnetic field. Diamagnetic substances, such as copper and carbon, are weakly repelled. While anti-ferromagnetic materials, such as chromium, have a more complex relationship with a magnetic field. The force of a magnet on paramagnetic, diamagnetic, and interferomagnetic materials is usually too weak to be felt, and can be detected only by laboratory instruments. So, in everyday life, these substances are often described as non-magnetic.

The strength of a magnetic field always decreases with distance from the magnetic source, though the exact mathematical relationship between strength and distances varies. Many factors can influence a magnetic field of an object, including the magnetic moment of the material, the physical shape of the object, both the magnitude and direction of any electric current present within the object, and the temperature of the object.

Magnetism was first discovered in the ancient world when people noticed that lodestones, naturally magnetized pieces of the mineral magnetite, could attract iron. The word for magnet comes from the Greek term magnetus lithus. The Magnesian stone, lodestone. In ancient Greece, Aristotle attributed the first of what could be called a scientific discussion of magnetism to the philosopher Salis of Miletus, who lived from about 625 BCE to about 545 BCE.

In ancient China, the earliest literary reference to magnetism lies in a 4th century BCE book named after its author, Guiguizi. The 2nd century BCE annals, Lu Xie Chunqiu, also notes, The lodestone makes iron approach. Some force is attracting it. A lodestone attracts a needle. The 11th century Chinese scientist, Shen Kuo, was the first person to write in the Dream Pool essays of the Magnetic Needle Compass, and that it improved the accuracy of navigation by employing the astronomical concept of True North.

By the 12th century, the Chinese were known to use the lodestone compass for navigation. They sculpted a directional spoon from lodestone in such a way that the handle of the spoon always pointed south.

Alexander Nacum, by 1187, was the first in Europe to describe the compass and its use for navigation.

In 1269, Peter Peregrinus de Maricour wrote the Epistola de Magnete, the first extant treatise describing the properties of magnets. In 1282, the properties of magnets and the dry compasses were discussed by Al-Shraf Umar II, a Yemeni physicist, astronomer, and geographer. In 1600, William Gilbert published his work on the magnet and magnetic bodies and on the great magnet, the Earth. In his work, he describes many of his experiments with his model Earth called the Torella. From his experiments, he concluded that the Earth was itself magnetic, and that this was the reason compasses pointed north, whereas previously, some believed that it was the Polestar Polaris, or a large magnetic island on the North Pole that attracted the compass. An understanding of the relationship between electricity and magnetism began in 1819, with work by Hans Christian Ersted, a professor at the University of Copenhagen, who discovered by the accidental twitching of a compass needle near a wire, that an electric current could create a magnetic field. This landmark experiment is known as Ersted's experiment. Jean-Baptiste Biot and Felix Savard, both of whom in 1820, came up with the Biot-Savard law, giving an equation for the magnetic field from a current carrying wire. Around the same time, André-Marie Ampère carried out numerous systematic experiments, and discovered that the magnetic force between two DC current loops of any shape, is equal to the sum of the individual forces that each current element of one circuit, exerts on each current element of the other circuit.

In 1831, Michael Faraday discovered that a time-varying magnetic flux, induces a voltage through a wire loop. In 1835, Carl Friedrich Gauss hypothesized, based on Ampère's force law, in its original form, that all forms of magnetism arise as a result of elementary point charges moving relative to each other. Wilhelm Edward Weber advanced Gauss's theory to Weber electrodynamics. From around 1861, James Clerk Maxwell synthesized and expanded many of these insides into Maxwell's equations, unifying electricity, magnetism, and optics into the field of electromagnetism. However, Gauss's interpretation of magnetism is not fully compatible with Maxwell's electrodynamics. In 1905, Albert Einstein used Maxwell's equations in motivating his theory of special relativity, requiring that the laws hold true in all inertial reference frames. Gauss's approach of interpreting the magnetic force as a mere effect of relative velocities Thus found its way back into electrodynamics to some extent.