The More You Know #6 – Metal Detectors are MAGIC?

In Physics by Mystifact

We have all heard of metal detectors; they are everywhere. If you have been on holiday, you have walked through one at Airport security. Some of you may have even had the luxury of playing with a handheld one to go on a treasure hunt. In practice, they work wonders; for example, they are good at stopping terrorists from travelling around, or even when looking for your parent’s ring in the garden after a family barbecue. How they work is fascinating and by the end of this article you will learn just that!

Electricity and Magnetism

When people see these two words they tend to run away – but please do stay! This will make sense and it certainly is interesting, I promise!

What is their relevance?

Imagine an inseparable pair of best friends, or a madly in love married couple; this is what electricity and magnetism are like. Where you see an electric field you see a magnetic field. Without this cute relationship between them, there are a lot of things we stop being able to do; for example, using a washing machine, vacuum cleaning, playing with computers – in fact, generating electricity would be impossible.


Electromagnets are simply the combination of electric fields and magnetic fields in some sort of machine. Let me tell you how electricity is generated using them, by talking about wind turbines (Figure 1) as an example [1]. When wind blows the turbine’s arms around, this motion causes copper wires inside it to start moving around. These wires are kept between a couple of magnets. What you now need to know now, is this golden rule, which we will refer back to later on:

When a conducting object (like a metal) is moved around a magnetic field, a current is generated in this metal. If there is a current in a metal there is a magnetic field around this current.

If you don’t understand this rule, it will all make sense in due course. Nevertheless, this is why wind turbines are a renewable source of energy because you cannot run out of wind and nothing is being wasted making this electricity.

How do metal detectors work?

The metal detector is basically made of 2 coils, one in one circuit, the other in another [2]. One coil is called the transmitter coil, the other is called the receiver coil. When you switch the detector on, the current flowing through the transmitter coil ‘creates’ (or induces) a magnetic field. When you start to wave your detector about, you are moving this magnetic field.

Remember our golden rule?

If this magnetic field (from the transmitter coil) passes through a metal ring, which conducts electricity, what happens to it? A current is produced within this ring, due to electromagnetism. Now since there is a current, again, using the golden rule, it induces a secondary magnetic field around it (the ring). This secondary magnetic field is picked up by the receiver coil in the detector, which is connected to a buzzer.

Again, referring to our golden rule:

The magnetic field in the metal ring causes a flow of current in the receiver coil which causes the buzzer to go off. There you have it, how a metal detector works. Amazing, right?

If you have any questions, leave them below and until next time, take care.

~ Mystifact


Please note; no copyright infringement is intended. All images used have been labelled for re-use on Google Images. If any artist or designer has any issues with any of the content used in this article, please don’t hesitate to contact me to correct the issue.

Previous ‘The More You Know’ posts:
The More You Know #1 – How to lose weight if you are 100% desperate
The More You Know #2 – Bees have spidey senses!
The More You Know #3 – The Human Race in a Sugar Cube?
The More You Know #4 – Human vs. Hydrogen Bomb
The More You Know #5 – The Physics behind the PERFECT free kick

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