Magnetic Flux: The Invisible River Running Through Everything
A plain-language guide to one of physics’ most important (and most misunderstood) concepts
What Is Magnetic Flux?
Imagine you’re standing in a river holding a hula hoop. The amount of water flowing through that hoop every second depends on three things: how fast the river is flowing, how big the hoop is, and what angle you’re holding it at. Turn the hoop to face the current head-on and you get maximum flow through it. Turn it sideways, edge-on to the current, and nothing passes through.
Magnetic flux works exactly the same way — except instead of water, it’s an invisible magnetic field flowing through a surface.
Magnetic flux is simply a measure of how much magnetic field passes through a given area.
That’s it. No mystery. It’s the magnetic equivalent of “how much water flows through this hoop.”
Why Should You Care?
Because magnetic flux is the basis of almost every electrical device you use:
- Your phone charger works because changing magnetic flux generates electricity (that’s what the transformer inside it does)
- Electric motors in your car, blender, and washing machine all work by manipulating magnetic flux
- Generators at power plants convert spinning motion into electricity by changing the flux through wire coils
- MRI machines use extraordinarily precise magnetic flux to image the inside of your body
- Wireless charging pads transfer energy through flux coupling between coils
The single most important law connecting magnetism and electricity — Faraday’s Law — says: a changing magnetic flux creates an electric voltage. That one sentence is the foundation of modern civilization’s electrical infrastructure.
The Units: A Simple Guide
Physics has a few different units for measuring magnetic fields and flux. Here’s the plain-language breakdown:
Measuring the Field Strength (How Fast the “River” Flows)
| Unit | Symbol | Scale | Where You’ll See It |
|---|---|---|---|
| Tesla | T | The SI (official science) unit | MRI machines, lab research, engineering specs |
| Gauss | G | The older, smaller unit. 1 Tesla = 10,000 Gauss | Earth’s field, magnets, everyday magnetism |
Everyday examples:
- Earth’s magnetic field at the surface: ~0.5 Gauss (0.00005 Tesla)
- Earth’s magnetic field at the core: ~25 Gauss
- A refrigerator magnet: ~50 Gauss
- An MRI machine: 15,000–30,000 Gauss (1.5–3 Tesla)
- The strongest sustained lab magnet ever: ~450,000 Gauss (45 Tesla)
Measuring the Total Flux (How Much “Water” Goes Through the “Hoop”)
| Unit | Symbol | What It Means |
|---|---|---|
| Weber | Wb | The SI unit of magnetic flux. 1 Weber = 1 Tesla passing through 1 square meter |
| Maxwell | Mx | The older CGS unit. 1 Weber = 100,000,000 Maxwells |
The relationship is straightforward:
Flux = Field Strength x Area x cos(angle)
If you have a 1 Tesla field passing straight through a 1 square meter surface, that’s 1 Weber of flux. If you tilt the surface 60 degrees, you get half a Weber (because cos 60 = 0.5).
The Flux Quantum: Where It Gets Weird
At the quantum scale, magnetic flux comes in discrete packets — like how water seems continuous but is actually made of individual molecules. The smallest possible unit of magnetic flux in a superconductor is called the flux quantum:
Phi-0 = 2.07 x 10^-15 Weber
This is an incredibly tiny amount. But it’s one of the most precisely measured constants in all of physics, and it shows up everywhere in superconductor behavior. When a magnetic field penetrates a superconductor, it does so in exact multiples of this quantum — never a fraction of it. Each unit of penetrating flux forms a tiny tube called a vortex or fluxon.
The Key Concepts in Plain English
Flux Density vs. Total Flux
Think of it like rain:
- Flux density (measured in Tesla or Gauss) is how hard it’s raining — drops per square foot per second
- Total flux (measured in Weber) is how much water collects in your bucket — it depends on both how hard it’s raining AND how big your bucket is
A strong field through a small area can give the same total flux as a weak field through a large area.
Changing Flux = Electricity
This is Faraday’s Law, and it’s the most practically important thing about flux:
If the amount of magnetic flux through a loop of wire changes — for ANY reason — a voltage appears in the wire.
It doesn’t matter why the flux changes:
- Move a magnet toward the loop -> flux increases -> voltage
- Move it away -> flux decreases -> voltage (opposite direction)
- Spin the loop in a steady field -> flux oscillates -> alternating voltage
- Keep everything still but increase the field -> voltage
This is how generators work. This is how transformers work. This is how your wireless charger works. This is how electric guitars pick up string vibrations. One principle, countless applications.
Flux Pinning: Locking Magnetism in Place
In a superconductor, something remarkable happens: magnetic flux can get pinned — locked in place by tiny defects in the material. The flux vortices (those quantum tubes of magnetic field) get trapped and cannot move.
This is why you see those dramatic demonstrations of superconductors hovering locked in mid-air above magnets. The flux is pinned. The superconductor literally cannot move because the magnetic field lines threading through it are anchored to specific points in the material. Push it sideways, and it springs back. Flip it upside down, and it still holds position. The magnetic flux is frozen in place.
The strength of flux pinning determines how useful a superconductor is for practical applications. Weak pinning means the flux vortices can creep and slide, creating a tiny pseudo-resistance that degrades performance. Strong pinning means rock-solid locking with zero energy loss.
Flux in Nature
The Earth’s Magnetic Field
The Earth generates a magnetic field from convection currents of molten iron in its outer core. At the core, this field is roughly 25 Gauss. By the time it reaches the surface, it has spread out and weakened to about 0.25–0.65 Gauss depending on your latitude and local geology.
This field is what makes compasses work, protects us from solar radiation, and provides the baseline magnetic environment that every living thing on Earth has evolved within. It’s weak by engineering standards — tens of thousands of times weaker than a medical MRI — but it’s omnipresent and essential.
Animal Navigation
Birds, sea turtles, salmon, honeybees, and possibly many other species can detect the Earth’s magnetic flux and use it for navigation. The mechanism isn’t fully understood, but it appears to involve either magnetite crystals (tiny biological magnets) or quantum effects in certain proteins called cryptochromes. Either way, these animals are biological flux sensors — they can feel what our instruments measure.
Flux in Technology
Transformers (Why Your Phone Charger Works)
Your phone needs about 5 volts. Your wall outlet provides 120 volts (in the US). A transformer converts between them using magnetic flux:
A coil of wire creates a magnetic field (flux) in an iron core. A second coil wrapped around the same core picks up that flux. If the second coil has fewer turns than the first, the voltage drops proportionally. Changing the ratio of turns changes the voltage ratio — and it’s all mediated by magnetic flux flowing through the shared core.
Electric Motors
Every electric motor converts electricity into spinning motion by manipulating flux. Current flowing through coils creates magnetic flux that interacts with permanent magnets (or other coils), producing torque. The efficiency of the motor depends on how well the flux is directed and controlled. Better flux management = more efficient motor = less wasted energy as heat.
Hard Drives
Your computer’s hard drive (if it’s not an SSD) stores data as patterns of magnetic flux on a spinning disk. Each tiny region is magnetized in one direction or another — representing a 0 or 1. The read head detects changes in flux as the disk spins beneath it, converting magnetic patterns back into digital data. Every document, photo, and song stored on a magnetic hard drive is literally a pattern of magnetic flux.
Quick Reference Card
| What You Want to Know | Unit | Example |
|---|---|---|
| How strong is this magnet? | Gauss or Tesla | Fridge magnet: ~50 G |
| How much total field passes through this area? | Weber | Transformer core: ~0.01 Wb |
| What’s the smallest flux unit in a superconductor? | Flux quantum (Phi-0) | 2.07 x 10^-15 Wb |
| How fast is the flux changing? | Weber per second = Volts | Generator output |
| How well does this superconductor hold flux? | Activation energy (Kelvin) | YH6: ~10,000–70,000 K |
The Takeaway
Magnetic flux is invisible, silent, and easy to ignore — but it’s the mechanism behind every motor, every generator, every transformer, and every wireless charger on the planet. It’s how the Earth shields us from solar radiation, how birds find their way home, and how your data is stored on a hard drive.
Understanding flux — really understanding it as a physical quantity that flows, gets pinned, changes, and generates voltage — opens the door to understanding how electromagnetism actually works in practice. Not as abstract equations, but as an invisible river of force that we’ve learned to channel, direct, and harness.
And we’re still learning. The behavior of magnetic flux inside superconductors — how it quantizes, how it pins, how it interacts with acoustic vibrations in the lattice — is at the frontier of physics right now. The next breakthroughs in energy, transportation, and computing may all come down to understanding flux just a little bit better than we do today.
This is a companion piece to the Wave Coherence Model of Superconductivity (PART) research papers. For the full theoretical framework, see the PART v2.0 working paper.