How to find north pole of ring magnet

Ask questions:

It is well known that block magnet has two small poles (N and S). So, do ring magnets have poles? If so, how are the poles distributed?

Conjecture and hypothesis

According to Ampere’s molecular circulation theory, block magnet are all aligned by magnetic molecules to form magnetic poles (as shown in Figure 1). The material of the ring magnet is the same as that of the strip magnet, and the magnetic molecules should also be aligned to form the magnetic poles. It is conjectured that the pole distribution of the ring magnet may be as follows:

• ① The magnetic poles are laterally distributed, as shown in Fig.2A;
• ② The magnetic poles are axially distributed, as shown in Fig.2B;
• ③ The magnetic poles are distributed radially, as shown in Fig.2C.

Figure 1

Figure 2

Design scheme and experiment

We collect a wide range of ring magnets and do a lot of experiments.

Directivity experiment

As shown in Figure 3 on the following page, suspend the ring magnet with thin wire:

Figure 3
Phenomenon: Fig.3A shows no directivity; FIG. 3B shows a certain directivity, but it is not as obvious as a bar magnet, so it is difficult to point north and South stably.
Conclusion: it is impossible to determine whether there are magnetic poles and their distribution, so further experiments are necessary.

Iron powder experiment

Put the ring magnet into the scrap iron, and then gently shake the magnet, showing the distribution as shown in Figure 4.

Figure 4
Obviously there are magnetic poles. The transverse distribution can be ruled out, because the thickness of the magnet is not enough, it is difficult to determine the axial or radial distribution. Further research is needed. However, the possibility of transverse distribution of magnetic poles can be ruled out, that is to say, conjecture ① is wrong.

Interaction experiment

Figure 5 shows the experimental results: only mutual exclusion, not mutual attraction. Therefore, the possibility of radial distribution can be ruled out! Fig. 6 experimental results: the radial distribution of the ring magnet is confirmed. And saw the magnetic levitation phenomenon.

Figure 5

Figure 6

Determination of the north and south poles

Because the height (thickness) of the ring magnet is generally small, the phenomenon of directivity experiment is not obvious, so it is difficult to determine the north and south poles. Figure 7 shows the effect on the small magnetic needle, and figure 8 shows the effect on the electrified straight wire, which can determine the north and south poles of the ring magnet.

Figure 7

Figure 8

It can be determined from the above experiments that the ring magnet has N and S poles just like the bar magnet. It is distributed along the axial direction of the ring, as shown in Figure 8.

What is the magnetic field principle of ring magnet?
Ring magnet. The ring magnet made of hard magnetic material has no magnetism before magnetization. The position and number of magnetic poles depend on the way of magnetization. So the specific use, the number of poles depends on the customer.

What are the pole positions of common ring magnets?

Pole position:

• 1. Some have one or more pairs of magnetic poles in the outer ring of the ring;
• 2. Some have one or more pairs of magnetic poles in the inner ring of the ring;
• 3. Some of them are on the top and bottom of the ring (-N-S);
• 4. Some magnetic poles are on a ring end face and have one or more pairs of magnetic poles.

The distribution map of the magnetic induction line of the circular magnet is also a hot topic for many netizens. The following section provides the distribution map of the magnetic induction line of the circular magnet for reference.
As mentioned earlier, the magnetic field distribution of the ring magnet is also related to your magnetization direction. The axial, radial, multipole and monopole magnetic field distribution will be different.
The distribution of magnetic induction line of ring magnet

How to find north pole of ring magnet?

There are two kinds of magnetic poles for ring magnets, if the ring magnet is axially magnetized, the magnetic pole is at two end faces; if it is radially magnetized, it is at the diameter direction of the ring:

• 1. The magnetic poles are distributed transversely, with N poles on the outside and S poles on the inside.
• 2. The magnetic poles are axially distributed, with N poles on the top and S poles on the bottom.

Here is how to distinguish the north and south poles of a ring magnet:

Method 1: the magnet can be freely rotated in the horizontal plane by hanging it with a thin wire. When the magnet is stationary, it will point to the north-south direction, with N pole at the north end and S pole at the other end.
Method 2: take a compass, and point one end of the magnetic stripe to the south near the compass (the magnetic field is the north pole). If it attracts each other, then this end is the south pole, and repulsion is the North Pole.
Method 3: one end of the magnet is close to the N pole of a small magnetic needle with known polarity, the N pole is repulsive, and the S pole is attractive.

Source: China Permanent Magnet Manufacturer – www.rizinia.com