How Does A Switchable Magnet Work?
A switchable magnet works by providing two alternate routes for the magnetic flux that have almost equal reluctance, so you need no force switch from one to the other. One path simply goes out through the face, and the other is shorted through the bar in the middle.
A magnetic switchable device (often called a magnetic base) is a magnetic fixture that uses one or more permanent magnets in a configuration that allows the external field to be turned on or off.
How Do Magnets That Can Be Turned On And Off Work?
First you have to know that magnetic fields are generated by moving charges. When there is a current, there is a magnetic field. Ampere’s equivalence principle tells us that, from far away, a current flowing in a coil is indistinguishable from a magnetic dipole.
Of course the magnetic field is a vector, so it has a magnitude and a direction. It is quite easy to prove that the magnetic field generated by a current flowing around a coil is proportional to the current. This means that increasing the current will increase the magnetic field, and in particular if you stop the current you will “turn off” the magnetic field. Furthermore, B is directed along an axis perpendicular to the coil (if you draw the coil on a piece of paper as a circle, the magnetic field is directed towards you).
It seems we have the ingredients to build a “magnet that can be turned off”, like you asked! These are called electromagnets, and they are made out of many coils. What happens is that, inside the coils, a magnetic field is generated. First, let’s talk about it’s direction. If one coil generates a field perpendicular to it, how will the field generated by many connected coils be directed? Of course, still perpendicular to them! And what will it’s magnitude be? It turns out, B =μ0Ni/l , where N is the number of coils and l the length of the electromagnet.
What does this mean? That once you built your electromagnet (with N coils and length l), you can control the magnetic field inside it by simply changing the current passing through the coils. To turn it off, just turn off the current!
Compare this with a permanent magnet. To produce a strong magnetic field, the electromagnet requires a lot of current, which means a huge power supply. Not only, but a current will dissipate energy in the form of heat, so it must also be cooled down, which is not easy at all. On the other hand, the permanent magnet requires no power, it just creates a magnetic field by existing.
What Is An On-off Magnet?
Most people would think that an on-off magnet is an electromagnet. When the electricity is switched on, it becomes a magnet. When the electricity is switched off, it stops being a magnet.
To be more accurately, that is not completely right. There are another 2 types of “on and off” magnet: permanent magnet with on and off switch device; electro permanent magnet switched on and off by electric current.
Electrically Switched On and Off Permanent Lifting Magnet
There is this type of magnet, that is switched on by electric current to release its magnetic force, and switched off by electricity too, to demagnetize itself. It is called electro-permanent magnet.
Electrically switched on and off permanent magnets, are conveniently turned on and off as the user requires. They have been widely used in different industries as magnetic chucks for grinding and milling ferrous items, lifting magnets for handling large heavy workpieces, and magnetic grippers on robotic arms in automation.
