Magnetic Field and Poles
Magnetism can be described through an invisible field and the poles that identify a magnet’s orientation. A compass needle responds to the field around a magnet, making part of its shape observable. Pole labels help explain why magnets sometimes move toward one another and sometimes push apart. A bar magnet offers a clear example of how these ideas describe magnetic behavior.
Magnetic field
A magnetic field is the region around a magnet where magnetic forces act on other magnets or magnetic materials. Because the field cannot be seen directly, diagrams use field lines as a visual model, not as physical threads.
- Direction: Outside a bar magnet, arrows run from north to south; inside it, the path returns from south to north again.
- Density: Closer-spaced lines indicate a stronger field in that region, while wider spacing indicates a weaker field; spacing is illustrative, not a measured scale.
- Closed paths: Each line forms a continuous loop: its outside segment runs north to south, and its inside segment returns south to north.
- No crossings: Lines never cross because the field has only one direction at any point; an intersection would imply two directions in the same location.
To map the field around a bar magnet, place it beneath paper and move a small compass to several marked points. Record the needle direction at each point, then connect the marks into a pattern.
North and south poles
A magnet’s north and south poles are the two opposing regions used to describe its orientation; on a bar magnet, they lie near opposite ends. The labels remain attached to the magnet, so turning it changes which direction each pole faces, not which pole it is.
Opposite poles attract: when the north pole of one magnet faces the south pole of another, the magnets pull toward one another. Like poles repel: north facing north, or south facing south, produces a push apart. The facing pole pair determines whether two magnets attract or repel.
When two bar magnets are brought together, turning one through half a rotation swaps the end facing the other magnet and changes the interaction from attraction to repulsion, or vice versa. For a quick check, bring the ends close without contact: attraction means opposite poles face; repulsion means like poles face.
Pull Force and Holding Force
Pull force is a measured load, not a universal measure of how securely a magnet will hold an object. The result applies to a particular magnet, counterface, contact condition, and loading direction. In use, coatings, gaps, geometry, and movement can differ from the test setup. Reading the number alongside its test conditions makes magnet strength specifications more useful for comparison.
Pull force
Pull force is the force required to separate a magnet from a ferromagnetic surface in a defined test setup. It is commonly reported in newtons (N) or pounds-force (lbf), and a test machine may record the peak load just before the magnet releases. The figure describes that separation event, not every way a magnet might be used.
In an installed application, magnetic holding force can differ from the test result. A magnet supporting a steel panel, for example, may face an angled load, vibration, or movement rather than a straight pull away from the surface. Those conditions affect how the assembly behaves, so the measured pull force should be treated as one comparison value, not a complete prediction of performance. Check that the reported result matches the kind of load the assembled part will experience.
Test conditions
A pull-force chart is comparable only when its test details are clear. Small changes at the magnet-to-steel interface or in the direction of loading can change the result.
- Contact: Full-face contact differs from contact across a spacer. Paint, adhesive, or a small air gap increases separation and can lower the measured force.
- Test material: Steel composition and thickness matter; a thin sheet may respond differently from a thick, flat steel plate used as a counterface.
- Surface condition: Rust, dirt, roughness, or a curved surface can reduce the area of close contact compared with clean, smooth, flat surfaces.
- Direction: Direct separation pulls the magnet away from the surface, usually at right angles; sliding loads act parallel to it and measure different behavior.
- Test setup: A fixture that pulls steadily and records release may not represent a part exposed to vibration, an edge load, or uneven contact.
A laboratory value therefore does not guarantee the same performance in every installation, even when the magnet model is identical. For a practical choice, compare results from similar setups and consider the actual load direction and contact surfaces.
Magnet Grade and N-Grade
Magnet grades describe properties of the magnetic material under defined conditions. For neodymium magnets, labels such as N35 and N52 summarize material performance, not every characteristic of a finished part. The grade can help compare materials, but it cannot predict how a particular magnet will perform in an assembly. Dimensions, finish, and the conditions of use also matter.
What a grade indicates
A magnet grade summarizes the performance of its magnetic material under specified test conditions. In common neodymium-iron-boron (NdFeB) nomenclature, N35 and N52 identify different material grades. Their numbers correspond approximately to maximum energy product in megagauss-oersteds (MGOe): N35 is about 35 MGOe, while N52 is about 52 MGOe. Maximum energy product is a material property, not a direct measure of the force a finished magnet will exert in every setup.
Neodymium magnet grades help compare material capability on a like-for-like basis. A higher number generally indicates a higher maximum energy product, so N35 vs N52 magnets can differ in the magnetic material available for a given volume. The label does not mean that every N52 part will outperform every N35 part in every application: dimensions and the completed design affect the result. Grade data are measured under defined conditions, and manufacturers may publish additional properties, such as remanence and coercivity, on a technical datasheet. Check the specific datasheet when comparing grades from different suppliers.
What it does not indicate
A material grade alone does not specify the finished magnet’s holding force, geometry, protective finish, or suitability for a particular operating environment. These properties depend on the part’s design and the conditions it will face.
| Property | What the grade does not provide | Additional information needed |
|---|---|---|
| Holding force | N35 or N52 is not a force value in newtons or pounds. | Part dimensions, contact area, air gap, and the mating material all affect the result. |
| Shape | A grade does not define geometry: a 10 × 2 mm disc and a 20 × 2 mm disc can share a grade. | Diameter, thickness, shape, and magnetization direction must be specified. |
| Coating | N35 does not identify a finish such as nickel-copper-nickel, epoxy, or zinc. | Coating material and thickness depend on the product specification and intended environment. |
| Operating suitability | The base grade does not establish a universal maximum operating temperature. | Common NdFeB designations include N, M, H, SH, UH, and EH; typical nominal limits range from about 80°C for N to 200°C for EH, with manufacturer-specific values. |
Use the grade to compare material capability, then select from a finished-part datasheet that gives the required dimensions, coating, and operating limits. That combination is more useful for choosing a magnet than the grade label alone.
Gauss and Magnetic Flux Density
Magnet specifications may describe field density, material grade, or mechanical performance, and those labels are not interchangeable. A gauss value refers to magnetic flux density at a measurement point. Its meaning depends on the setup used to obtain it. Reading both the unit and the measurement context makes a magnet gauss rating easier to interpret.
Gauss
Gauss (G) is a unit of magnetic flux density, the quantity used to describe a magnetic field at a point. It belongs to the centimeter-gram-second (CGS) system; the SI system expresses magnetic flux density in tesla. A gauss value is a field measurement, not a description of a magnet’s material composition.
That makes it different from a magnet grade, which identifies a magnetic material class, and from a pull-force rating, which expresses force under a specified test arrangement. A magnet gauss rating can describe a field reading at a chosen location, but it does not by itself state how much load the magnet will hold. Treat gauss as a unit for magnetic field intensity, not as a universal score for neodymium magnet strength.
Measurement context
Even for the same magnet, a gaussmeter reading can change with the setup. Check these details before comparing values:
- The location matters because field density varies across a magnet; a reading near an edge may differ from one taken over the center of the same face.
- A probe aligned with the field detects a different component than one turned sideways, so record its orientation relative to the magnet’s surface.
- Distance affects the reading: moving the sensor away from the magnet changes the field it detects, even when the probe remains on the same axis.
- The measurement method matters because sensor type, calibration, and how the probe is positioned can affect the reported value from a gaussmeter.
- Results from different locations, orientations, distances, or instruments are not automatically comparable; compare readings only when the measurement setup and point are matched.
Record the point, orientation, distance, and method alongside each result. That context makes repeated surface-field measurements useful for comparison.