An initially unmagnetized bar of nickel is placed in a strong uniform magnetic field at
PHYSICS · Single correct · CBSE · Physics · Magnetism and Matter · Magnetism and Matter
Problem
An initially unmagnetized bar of nickel is placed in a strong uniform magnetic field at 25∘C. While the field remains on, the bar is heated to 700∘C and then allowed to cool back to 25∘C after the field is turned off.
Which statement best explains why the bar shows almost no permanent magnetization at the end of this process?
(a) While the bar was heated, eddy currents generated internal magnetic fields that opposed the external field, so its domains never aligned and no permanent magnetization remained after cooling.
(b) Heating to 700∘C increases the magnetic permeability of nickel, causing the domains to lock in random directions as it cooled.
(c) The bar lost magnetization because heating it above its Curie temperature destroyed long-range domain alignment, and the domains did not realign when the external field was later removed.
(d) Cooling in the absence of a field reduces the magnitude of each atomic magnetic dipole moment to nearly zero, eliminating any net magnetization.