While most see magnets as a novelty item there's no denying how complex these pieces of metal are. To begin with, magnetism is an invisible force so they appear to work through magic, and then on top of that, they are usually very simple at first glance. A magnet is after all just a piece of metal to the naked eye.
And yet every magnet is completely different when it comes to its effectiveness. There are small magnets that seem almost impossible to separate from each other. Just like there are also large magnets that barely seem to work at all. On top of that, it's not like a magnet's strength is consistent.
Anybody who has owned a bar magnet can tell that the poles are incredibly strong but the sides barely have any effect. So to understand where a magnet's strongest and weakest point, today we'll take a look at how magnetism is related to the size and shape of a magnet.
Where is a Magnet the Strongest and Weakest?
Generally speaking, a magnet is at its strongest at either of its two poles, however, defining the poles of a magnet can be tricky depending on its shape.
Using a regular bar-shaped magnet as an example it's pretty easy to tell that its tips are the strongest points, meaning that these are the two poles.
The poles are basically what we think of as the positive and negative charges of a magnet, which means that if you have doubts about where they are you can simply grab another magnet and identify the two points where they attract or repel each other.
The reason why magnets are at their strongest on either of the poles is due to the fact this is the area where their magnetic fields start spreading from. We will learn more about magnetic fields soon, but for now, you can think of them as the range of efficacy of each magnet. So logically they'll be at their strongest near their origin point.
Following the same logic, a magnet is at its weakest near the middle of its two poles. So in a bar magnet, the center would be the weakest, a horseshoe magnet would start faltering at the top of its curvature and a disc magnet is weaker at its edges.
The closest both poles are to each other the harder it will be to find the weak and strongest points in a magnet, but it all comes down to the distance from the poles.
What is the Magnetic Field?
To fully understand how magnets work, as well as why the poles are so important to their strength we need to discuss the concept of a magnetic field. As we all know magnetism is ultimately invisible to the naked eye, as far as our senses can tell nothing is pulling a piece of metal towards a magnet. But logically this isn't the case, and it all comes down to their magnetic fields.
Magnetism is derived from the unique orientation and charge of the electrons inside a piece of metal. So in general magnets can be said to operate and work at an atomic level. These particles generate a series of forces or vectors that we call the magnetic field.
So from each pole of a magnet, there are countless invisible forces born from these charges that are constantly interacting with their environment. These invisible forces can be seen as each pull or push a magnet makes, and are the reason why magnets can affect metals in the first place.
Since magnets are at their strongest at their poles this means that their magnetic field generally speaking starts on these poles. And since the strength of these fields falls off at an accelerated pace the further you get from the fields this also explains why the middle of a magnet tends to be its weakest point.
At What Distance Does the Strength of the Poles Start to Weaken?
By now we understand that the poles of a magnet are the strongest point of a magnet since this is where a magnetic field originates, but how noticeable is the difference compared to the rest of the magnet? Most household magnets are after all fairly small, so the “middle” point is almost next to the poles anyways. Would a magnet still have weaker spots in this case? How can we figure the actual strength of a magnetic field relative to its distance?
While in theory magnetic fields never run out of range, they do have one major weakness. And that is that their strength decreases at an incredibly accelerated rate. So no matter how vast the magnetic field is, any distance from the poles will make it weaker.
To calculate the strength of a magnet related to the distance from the poles all you need to do is to calculate the cube of the distance like this Effective Strength = 1/Cubed Distance.
Let's say at 1 cm away from the poles your magnet can still pick up coins. At 2 cm away the power will be just 1/8th of that, meaning that it likely will fail to pick the coin altogether. Now while this doesn't provide a numerical value to the strength of a magnet it does illustrate just how fast the strength of a magnetic field drops.
So no matter how small your magnet is, its middle point will only be one fraction of its original power. You can assume the weakest point of your regular household magnet will roughly amount to 1/27 of the strength of its poles, which in most cases will make its pull completely negligible.
Common Magnet Shapes and Their Strongest Points
Since magnets only need to be of the right material to be able to hold an electromagnetic charge, they come in countless shapes and forms. In fact, you could likely make a magnet in any shape provided you are willing to sacrifice the power of the poles and hence its efficiency.
However today we'll just focus on common shapes that see widespread use. While shape alone doesn't determine the overall power of a magnet they do play a role in how they work and where their poles are located, so understanding each shape can help you find its poles.
The most common example we've used today are bar magnets, these are usually rectangle-shaped. Due to this shape bar, magnets tend to have small poles which usually do result in a weaker magnetic field.
Disc magnets are very similar to flat bar magnets, but since their poles are on each side of the disc they are fairly broad. This ultimately means that they tend to be fairly strong for their size, and since their edge is usually negligible their weakest point isn't as notorious.
Sphere magnets might not look like they have unique poles, but they still do. There are imperceptible points on each end of the sphere that acts as the poles of the magnet, though you'll likely need another magnet to be able to identify them. Due to their shape sphere magnets aren't particularly strong and they are mostly used for their entertainment values.
Horseshoe magnets have one of the most interesting shapes in the market. Their poles are located at each tip of their “U” shape, which means both poles are pointing in the same direction. This means their magnetic pull is enhanced, similarly, their charge is almost null towards the other end.
Other Shapes and Sizes of Magnets
What Shape of Magnets is the Strongest?
The strength of a magnet is largely dependant on its material and age, however, the shape still plays a large role when it comes to its day-to-day efficiency. As we saw above Horseshoe magnets are the only shape in the market that makes both of its poles point in the same direction, and this means that when it comes to attracting metals they offer almost double the strength of other magnets.
Conclusion
A magnet's strength is tied to countless factors like material, age, shape, and internal orientation. However, regardless of these factors, they will always be at their strongest on their magnetic poles. The magnetic poles are where the “positive” and “negative” charges of a magnet can be found, and the invisible force of their magnetic field starts to spread from those poles.
This means that if you want to find the location where a magnet is the strongest or weakest all you need to do is identify its poles with the help of another magnet. Those points where a magnet is attracted or repelled are the poles, and the area near the middle of those poles will be the weakest part of your magnet.
Sources used:
- Strongest and Weakest Parts of a Magnet (thoughtco.com)
- What Is the Strongest Part of a Magnet? | Stanford Magnets
- What are magnetic fields? (article) | Khan Academy
- How Does Magnetism Work? | What are Magnets? (popularmechanics.com)
- The Various Shapes of Magnets and Their Uses | Apex Magnets Blog
- Which Shape of Magnets Is the Strongest? Learn About the Perfect Shape (magnetpartner.com)
- Q & A: magnet at a distance | Department of Physics | University of Illinois at Urbana-Champaign
