How to melt a matel in a short time.

I once saw a very interesting and amazing video. In the video, someone used a big coil that had been conducted to melt a metal. He put a metal above the coil and made electric current that keep running in the coil. A few seconds later, the metal turned red and melted.

Here's the video:

This video comes from :https://www.youtube.com/watch?v=8i2OVqWo9s0

That's very cool isn't it? Although it looked like magic, there was no magical about it. Instead, it's because of the law of physics. This big electric coil is made with copper, a metal that has high conductivity. This kind of metal can allow electric current to pass with a low resistance, so it is normally be used as the material of wire. According to Ampere's circuital law, a given current is associated with a magnetic field. If the current forms a closed loop(like the coil in this video), there will be a magnetic field as well, and this magnetic field is related to the electric current. To know the direction of the magnetic field, you have to use your right hand, and curl your fingers to the direction where current circuits. The direction of your thumb will be the direction of magnetic north pole.


After knowing that, we can start to understand why the metal in the video can be melted in 3 minutes. The reason is that the electric current within the coil is very strong, and it keeps changing its direction. We call this type of current "alternative current" because it constantly change its direction . This kind of current is used in our daily lives because of its ability to reduce the lost of energy. In this video, this guy used this alternative current because of other reasons. When the direction of current is changed, the direction of magnetic field is changed as well, and when a piece of metal is placed in a changing magnetic field, according to Lenz's law, electric current will be induced. If the magnetic field keeps changing, the current will keep existing in the metal. As long as the current is running in the metal, it generates heat because of the electric resistance. In this video, the current in the copper coil is strong, so the induced current in the metal is strong, too. In the same material, the stronger the current, the more heat will be generated. That's why the metal in the video can be heated up very quickly and melted in the end.