GEOLOGY

Detailed explanation-1: -The magnetic field disappears when the current is turned off. The wire turns are often wound around a magnetic core made from a ferromagnetic or ferrimagnetic material such as iron; the magnetic core concentrates the magnetic flux and makes a more powerful magnet.

Detailed explanation-2: -Heating the magnet to high temperatures or generating a magnetic field with an alternating current in the vicinity of the magnet are two ways to demagnetize it (assuming you want to do so). The simplest way to demagnetize it, however, is with a hammer.

Detailed explanation-3: -Electromagnets can be turned on or off and their strength can be changed by controlling the electric current. An electromagnet is a solenoid wrapped around a bar of iron or other ferromagnetic material. It is stronger if there are more turns in the coil of wire or there is more current flowing through it.

Detailed explanation-4: -You can increase the current in the solenoid. You can add more loops of wire to the solenoid. You can wind the coils of the solenoid closer together. You can use a stronger ferromagnetic material for the core.