A steel sewing needle is magnetized by stroking it repeatedly with the North pole of…
PHYSICS · Single correct · CBSE · Physics · Magnetism and Matter · Magnetism and Matter
Problem
A steel sewing needle is magnetized by stroking it repeatedly with the North pole of a strong bar magnet. The needle is then heated until it glows dull red, gently tapped on a table while aligned along Earth’s geographic North–South line, and allowed to cool to room temperature in that orientation. Which statement best describes the needle’s final magnetic state?
(a) It regains its original strong magnetization with the same polarity because the domains quickly realign as they cool.
(b) It retains only a weak magnetization aligned with Earth’s field because heating randomizes the domains and cooling in Earth’s weak field allows partial realignment.
(c) It becomes completely non-magnetic because heating permanently destroys the ferromagnetic domains.
(d) It acquires a strong magnetization opposite to its original polarity because tapping reverses the orientation of all domains while they are hot.