What method can magnetize iron and steel?

Rubbing with a magnet is the correct method for magnetizing iron and steel. This technique, known as "friction magnetization" or "contact magnetization," involves taking a permanent magnet and stroking it along the length of the iron or steel object. By aligning the magnetic domains within the material, the process imparts a magnetic charge to the object.

When the magnet is rubbed over the metal, the magnetic field induces magnetization in the material, causing the atoms to align in a specific direction, which results in the material itself becoming a magnet. This method is simple and effective for small objects or tools like nails and screws, where one might need a temporary magnet.

In contrast, heating with electric current would involve a much different process, primarily used in induction heating, but is not a direct method of magnetizing a material. Submerging metal in liquid nitrogen does not influence its magnetic properties; this method is often used to study the effects of superconductivity or cryogenics but is not a means of magnetization. Coating with magnetic powder does not magnetize the base material; rather, it could create a surface that has magnetic properties due to the powder but does not fundamentally change the magnetic characteristics of the underlying iron or steel.