The expansion and contraction of a magnetic material under a changing magnetic field is called?

• A. Magnetostriction
• B. Piezoelectricity
• C. Refraction
• D. Rarefaction

Answer: (A)

Magnetostriction is the change in dimensions a magnetic material experiences when its magnetization changes due to a magnetic field. This happens because magnetic domains reorient and interact with the crystal lattice, creating small strains through magnetoelastic coupling. As a result, the material can expand or contract along directions related to its magnetization, depending on the material’s properties.

This phenomenon is key in ultrasonic testing when using magnetostrictive transducers, where an alternating magnetic field drives the material to generate ultrasonic waves, and conversely, mechanical waves can affect the magnetic state.

The other terms don’t fit here: piezoelectricity involves electric polarization in response to mechanical stress (or vice versa), not magnetic-field-induced strain; refraction is the bending of waves as they pass between media with different speeds; rarefaction refers to the low-density phase of a sound wave, not a material’s response to a changing magnetic field.