Question

Which action will demagnetise a magnetised piece of steel?

a. cool it in a freezer for several hours.
b. hit it repeatedly with a hammer.
c. put it in a coil carrying a direct current (d.c.).
d. put it near an unmagnetised piece of iron.

Answer 1

The action that will demagnetize a magnetized piece of steel is (C) put it in a coil carrying a direct current (D.C.).

What occurs in this phase?

Put it in a coil with D.C. is the most effective method for demagnetization. When a magnetized object is placed in a coil with a changing magnetic field (created by the d.c. current), the internal magnetic domains in the object start to align with the external field.

As the current is reversed and the field changes direction, the domains are unable to follow perfectly, eventually becoming randomized and demagnetizing the object.

Therefore, the controlled exposure to a changing magnetic field from the coil is the most efficient method for demagnetizing steel.