不存在磁单极

Whenever you split a magnet in half, you get another magnet. So basically when you split a magnet at exactly the line between North and South, whichever part you split will automatically divide itself into its opposing force. So suppose we split a magnet and get the North side. Immediately, the North side will split in half and spontaneously have a South side. So they are always bipolar, and never have only a North or South pole independent of each other.

When we think of charges, we think of electrons and protons. As we saw before, current is the flow of electrons -- we couldn't have made this assertion if charges could be isolated and then flow freely.

So electricity and magnetism are analogous in many senses. What is the analog of a monopole in magnetism?

Fun fact. The first of Maxwell's equations will, in mathematical form, read out this fact. See here to jump straight to the connection (not recommended if you do not know about Maxwell's equations in mathematical form).

It is unknown whether magnetic monopoles exist.

They simply cannot exist.

A magnetic monopole is a hypothetical arrangement in which a magnet is split and one North piece and one South piece are obtained. However, when the magnet is split, the half with north has half of the half immediately switch to south, and the half with south has half of the half immediately switch to north. Thus, these monopoles with a magnetic pole by itself are never obtained and are only hypothetical.