The Wonderful World of Magnetic Fields
Have you ever wondered why a compass always points north? Or how pigeons fly thousands of kilometres to return home? These mysterious phenomena are attributed to the invisible force of magnetic fields, and our Earth is a giant magnet. Next, I will introduce he basic knowledge of magnets in detail, hoping to be helpful in your daily life.
Definition of Magnets
A magnet is an object capable of producing a stable magnetic field, with its history tracing back to ancient Greece’s use of natural lodestone. At that time, people used it to create the earliest compasses, opening the door to human understanding of magnetic phenomena. As early as the 6th century BCE, the philosopher Thales observed that lodestone could attract iron filings, laying the foundation for magnetism studies.
Modern science reveals that the magnetism of a magnet originates from the numerous magnetic domains within its structure. You can think of them as tiny “magnetic communities” within the material. In unmagnetized materials, these domains are randomly oriented and cancel each other out. When they align in the same direction under an external magnetic field, the material exhibits strong macroscopic magnetism. Common man-made permanent magnets in our daily lives, such as neodymium iron boron magnets and ferrite magnets, can retain their magnetism for over a century at room temperature.
Composition of Magnets
The reason a magnet can generate a magnetic field around it is described by several key concepts that outline its magnetic field configuration:
Magnetic Axis: An imaginary straight line connecting the north and south poles of the magnet, representing the axis of symmetry for the entire magnetic field structure.
Magnetic Poles: The two regions at the ends of the magnetic axis, namely the north pole (positive pole) and south pole (negative pole). Magnetic field lines emanate from the N pole and enter the S pole, forming a closed loop.
Neutral Line: In a bar magnet, this is a plane perpendicular to the magnetic axis that separates the north and south magnetisation regions. In this area, the magnet’s own magnetic field strength is the weakest, serving as the boundary where the magnetic field direction transitions.
What Metals Can Magnets Attract?
When a magnet’s external magnetic field acts on other materials, the materials exhibit three main types of magnetic behaviour based on their internal electron magnetic moments’ response:
Ferromagnetism: Such as iron, cobalt, and nickel, where materials have strong net magnetic moments that greatly amplify and respond to the magnetic field, resulting in strong attraction by the magnet.
Paramagnetism: Like aluminium and platinum, which show a weak positive response to external magnetic fields, producing a very slight attraction.
Diamagnetism: Such as copper, silver, and carbon, which generate a small magnetic moment opposite to the external field, leading to weak repulsion.
Below is a simple table of magnetic properties for several typical ferromagnetic elements:
| Element | Electron Configuration | Strength |
|---|---|---|
| Fe | [Ar] 4s² 3d⁶ | Very Strong |
| Co | [Ar] 4s² 3d⁷ | Strong |
| Ni | [Ar] 4s² 3d⁸ | Moderate |
| Gd | [Xe] 6s² 4f⁷ 5d¹ | Moderate |
Do Magnetic Monopoles Exist?
The answer is no. this is a fundamental law of magnetism. Everyone knows that magnets always have two poles: the south pole (negative pole) and the north pole (positive pole). Some people have wondered: If I break a magnet in half, wouldn’t that give me a lone south pole and north pole? But in reality, what you get are two smaller, complete magnets. Why is that?
When you break a magnet with tools, you’re actually severing the material, but the magnetic field isn’t “cut.” Magnetic field lines are continuous and don’t break. Each fragment rearranges its internal magnetic domains to form a complete magnetic dipole, still with its own N and S poles. It’s like a broken string of beads where the beads automatically reassemble into two shorter strings.
Common Applications of Magnets
Magnets have a wide range of applications, all based on the magnetic axis. Here are some common applications:
| Application Example | Principle and Expansion |
|---|---|
| Compass | Needle aligns N pole with Earth's magnetic north, magnetic axis matches geomagnetic axis for direction reference. |
| Magnetometer | Detects magnetic axis direction and neutral line to measure geomagnetic strength. |
| DC Motor | Stator magnets interact with rotor magnetic axis. Current reverses poles for continuous rotation, neutral line optimizes commutator. |
| AC Generator | Rotor magnetic axis cuts stator coils to induce current, neutral line balances phases. |
| MRI | Superconducting magnets create uniform 1.5-7T magnetic axis field, RF pulses along axis excite hydrogen atoms. |
| Magnetic Navigation Capsule | External magnets drive capsule's internal magnetic axis for rotation and drug release, neutral line aids positioning. |
| Maglev Train | Magnetic axis interacts with track poles, neutral line controls levitation height for frictionless high-speed travel. |
| Magnetic Storage | Read/write head flips data bits using tiny magnetic poles, magnetic axis encodes 0/1 directions. |
| Magnetic Soft Robots | Magnetic axis bends soft body, neutral line assists path planning for minimally invasive surgery. |
Is Earth a giant magnet?
Yes, Earth is indeed a giant magnet composed of north and south poles. Earth’s magnetic field forms a vast magnetic shield tens of thousands of kilometres away, deflecting streams of charged particles from the sun and most high-energy cosmic rays, preventing it from suffering the fate of Mars, which lacked a global magnetic field and was gradually stripped of its atmosphere. A small number of charged particles trapped by the magnetic field flow towards the poles, colliding with the upper atmosphere to create the spectacular auroras.
1. Navigation and Positioning:
Earth’s magnetic field provides us with a natural and stable global directional reference frame, enabling the ancient compass to function as a pointing tool. In many navigation systems, geomagnetic sensor data is fused with data from other sensors to calibrate orientation and improve pointing stability.
2. Biological and Health Impacts:
The geomagnetic field is an indispensable navigation tool for many organisms. Migratory birds, turtles, salmon, and many other animals have been shown to possess keen magnetoresistance, relying on the geomagnetic field to complete their astonishing global migrations. This behaviour maintains the balance of ecosystems, the reproduction of species, and key natural processes such as agricultural pollination, indirectly ensuring the survival of human resources.
FAQ Summary
Can magnets be split? Yes, but you won’t get a magnetic monopole! Each fragment will reform a complete N-S pole pair.
Why don’t permanent magnets lose their magnetism? Permanent magnets have highly ordered internal magnetic domains, remaining stable for decades at room temperature.
Will Earth’s magnetic field reverse? Yes, it reverses every 200,000-300,000 years.
Does the 5G signal interfere with magnetic fields? 5G is a high-frequency electromagnetic wave that mainly interferes with electronic devices rather than static magnetic fields. The two do not directly conflict.
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