Why would you do that? want to detect metal? I don’t know… maybe you want to find some gold in the ground. You can dig up ALL the earth or find a place where there is gold before you kick. Or maybe you’re looking for buried metallic meteorites. You can even utilize a metal detector to find a ring lost on the beach. These devices are quite useful.
But do you know how they work? I see! When you think about it, it’s not obvious. There are different types of detectors, but they all rely on the same frigid physics of electric and magnetic fields. Let’s take a look, shall we?
Go with the flow
First, how do metals differ from other materials? Every solid object is made up of atoms, each of which has negatively charged electrons orbiting a positive nucleus. In nonmetals such as plastic or glass, electrons largely stick to their original atom.
However, in a metal like copper, the outer electrons float freely and are shared by all atoms. This is why current can flow through metal – if we apply an electric field, electrons will flow in a specific direction, which is called an electric current. Metals are conductive.
Faraday’s law
So how do you create an electric field? The simplest way is to simply apply a charge to the surface of a metal object by adding a few electrons to it – that’s what a battery does. Of course, this won’t work for our purposes though. You’ll need access to the metal before you find it, which doesn’t make sense.
But there is another way. It turns out that A changing magnetic field it also produces an electric field. This is the basic idea of Faraday’s law. If you move a magnet near a metal conductor, this movement creates a changing magnetic field, which produces an electric field. If this electric field occurs in a metal boom: a so-called eddy current is created.
And vice versa
It also works the other way around: just as a changing magnetic field produces an electric current, an electric current produces a magnetic field. Remember that senior science fair project where you wrap a wire around an iron nail and connect the ends to a battery? Once the juice flows out, the nail temporarily becomes magnetic and can grab paper clips.
But as we just saw, you don’t need batteries. The changing magnetic field creates eddy currents in the metal, which then produce their own magnetic fields. Wait! This is even crazier. Since these eddy currents produce magnetic fields, there will be interaction between the metal and the thing producing an alternating magnetic field.
You are now ready for your first very plain metal detector. To create a variable magnetic field, we will simply utilize a moving magnet. In the demo below, I placed a magnet on a coin and then quickly picked it up. The movement creates eddy currents in the coin, which create a magnetic field that interacts with the magnet. See? Coins are bouncing.