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Magnetic force is an invisible and intangible non-contact force that profoundly influences the world. Its most intuitive manifestation is the attraction and repulsion between magnets: the two magnetic poles, North (N) and South (S), adhere to the basic law of “opposite poles attract, as poles repel.” This macroscopic phenomenon is rooted in the order of the microscopic world. Within atoms, the tiny magnetic moments generated by electron motion and spin are the fundamental source. In ferromagnetic materials like iron, cobalt, and nickel, a large number of atomic magnetic moments spontaneously align in an orderly fashion, forming strong spontaneous magnetization, which manifests as the familiar macroscopic magnetic force we observe.
The Microscopic Origin of Magnetic Force
To deeply understand magnetic force, one must penetrate the surface of matter and delve into the atomic interior. All substances are composed of atoms, and the charge of electrons outside the atomic nucleus, combined with their ceaseless motion, makes each atom akin to a tiny magnet with an intrinsic magnetic moment.
However, the vast majority of substances do not exhibit magnetism at the macroscopic level. This is because the magnetic moments of their atoms or molecules are oriented randomly, canceling each other out, resulting in a near-zero net magnetic moment. Only in ferromagnetic substances does a special “exchange interaction” between atoms exist, prompting adjacent magnetic moments to spontaneously align in parallel, forming macroscopic magnetic domains and thereby producing strong collective magnetism. This explains why magnets can exert force “out of thin air.”
How to Measure Magnetic Force
In the 1830s, German mathematicians and physicists Carl Friedrich Gauss and Wilhelm Weber collaborated to invent an early magnetometer. Its main principle was to measure the strength and direction of the magnetic field by the deflection angle of a magnetic needle in the Earth’s magnetic field. They achieved the first quantitative study of the Earth’s magnetic field, opening a new chapter in geophysics.
What instruments are used to measure magnetic force?
| Instrument Type | Core Principle | Typical Sensitivity / Resolution | Main Application Scenarios |
|---|---|---|---|
| Fluxgate Magnetometer | Utilizes changes in induction intensity of a high-permeability core in a saturated magnetic field. | ~1 nT | Ground archaeology, engineering surveys, navigation. |
| Proton Magnetometer | Based on measuring the Larmor precession frequency of hydrogen protons in the geomagnetic field. | 0.1–0.01 nT | Mineral exploration, oil and gas structural surveys, regional geological mapping. |
| Optically Pumped Magnetometer | Utilizes quantum energy level transitions of specific atoms under light and magnetic fields. | Up to 0.001 nT (1 pT) | Airborne and UAV geophysical exploration, fundamental physics research. |
| Superconducting Quantum Interference Device (SQUID) | Based on the Josephson effect in a superconducting loop, measuring quantized changes in magnetic flux. | Up to 0.000001 nT (1 fT) | Extremely weak magnetic field detection, biomagnetic imaging, cutting-edge physics experiments. |
The Significance of Measuring Magnetic Force
The core purpose of magnetic surveying is to detect magnetic anomalies caused by differences in the magnetic properties of near-surface subsurface media, thereby inferring subsurface structures and the spatial distribution of materials. These differences mainly stem from variations in the induced magnetization and remanent magnetization of rocks and minerals. Magnetic surveying is efficient, economical, and has a wide coverage, making it suitable for all stages of detailed exploration.
Applications of Magnetic Force
By capturing these subtle changes in magnetic fields with high-precision magnetometers, we can locate, image, and study invisible subsurface targets without disturbing the Earth’s surface. Its main applications are as follows:
Mineral Resource Exploration: Directly detecting deposits rich in strongly magnetic minerals. Alteration zones or structures associated with certain metallic ores can produce indirect magnetic anomalies, providing clues for mineral exploration.
Oil and Gas Structural Research: Primarily used to identify sedimentary basin boundaries, determine basement depth and undulation, and trace major deep faults, providing crucial data for assessing oil and gas prospects and regional geological structures.
Engineering and Environmental Surveys: Used to detect concealed faults, karst caves, and other geological hazards.
Archaeological Exploration: Ancient human activities often produce significant thermoremanence due to heating or the presence of magnetic materials, creating a striking contrast with the surrounding soil.
Some FAQs
Why can magnets attract or repel each other?
The fundamental source of magnetism is the microscopic magnetic moment generated by the movement and spin of electrons within atoms. In ferromagnetic materials, the microscopic magnetic moments between atoms spontaneously align in parallel, forming macroscopic magnetic domains, thereby generating a powerful magnetic force.
Are all metals attracted to magnets?
No. Only metals containing ferromagnetic elements such as iron, nickel, and cobalt are strongly attracted. Metals like copper, aluminum, gold, and silver are not attracted to magnets, even though they are also metals.
Do magnets have a single pole?
No. All magnets have complete north and south poles. Even if you cut a magnet in half, each half will still have complete north and south poles.
How is magnetic force measured?
The earliest quantitative measurement was invented in the 1830s by German scientists Carl Friedrich Gauss and Wilhelm Weber. They used the deflection angle of a magnetic needle in the Earth’s magnetic field to measure the strength and direction of the magnetic field, known as an early magnetometer.
What are the important applications of magnetic force in modern life?
Magnetic force is used to manufacture permanent magnets and controllable electromagnets, driving technologies such as electric motors, generators, and hard disk storage. In the future, it may be used for early warning of natural disasters like earthquakes and volcanoes.
Will magnets lose their magnetism over time?
Permanent magnets can maintain their magnetism for decades or even longer under normal conditions. However, high temperatures and strong external magnetic fields can accelerate their demagnetization.
Conclusion
In ancient times, people were fascinated by the attraction between magnets, as if it were a secret power bestowed by heaven. Through long-term exploration, humanity gradually mastered the magnetic properties of lodestone and, based on this, invented high-performance permanent magnets of different grades, and even electromagnets that could be switched on and off at will. This is not merely technological progress, but also a crystallization of human wisdom.
Today, research in magnetism allows us to fully reveal underground geological structures using an invisible force exerted by the Earth itself. We can now expect to provide early warnings of developing natural disasters such as earthquakes and volcanoes, buying precious time to protect lives and homes.
For more insights, check these related blogs:
- Basic knowledge of magnetic field strength
- Comprehensive Guide to Electromagnetic Energy
- What Metals are Magnetic or Not Magnetic?
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