Materials science and dielectrics — assertion–reason on electro-mechanical coupling Assertion (A): In many dielectric materials, applying an electric field (and thus producing dielectric polarization) can cause mechanical distortion of the solid. Reason (R): If dielectric polarization causes mechanical distortion, then the converse must always hold; namely, any mechanical distortion will necessarily cause dielectric polarization in that material.

Introduction / Context:
This assertion–reason problem tests your understanding of electro-mechanical coupling in dielectric solids, including electrostriction and piezoelectricity. An applied electric field can polarize a dielectric and, in some classes of materials, induce strain; however, the logical converse is not universally guaranteed.

Given Data / Assumptions:

• Dielectric polarization can arise from electronic, ionic, or orientational mechanisms when an electric field is applied.
• Mechanical distortion refers to macroscopic strain in the solid.
• “Many materials” implies a broad class, not only special crystals.

Concept / Approach:
All dielectrics exhibit electrostriction, a quadratic coupling where strain is proportional to the square of the electric field (or polarization). Certain non-centrosymmetric crystals also exhibit the piezoelectric effect, a linear coupling where strain is proportional to the field and, conversely, stress/strain produces polarization (the converse effect). Thus, while it is broadly true that dielectric polarization can produce mechanical distortion (A is true), the converse statement is only guaranteed for piezoelectric materials. It is not a universal rule for “many materials,” so R is false as a general statement.

Step-by-Step Solution:
Establish that electrostriction exists in all dielectrics: polarization → strain (quadratic), so mechanical distortion may occur.Recognize that piezoelectricity is a special case requiring non-centrosymmetric crystal structures; only then does the converse (mechanical stress → polarization) necessarily hold.Therefore, the assertion (A) stands, but the reason (R) overgeneralizes and is false.

Verification / Alternative check:
Standard materials texts distinguish electrostriction (universal, quadratic) from piezoelectricity (conditional, linear). Many polymers and centrosymmetric crystals show electrostriction but not piezoelectricity; applying mechanical stress to such materials does not generate net polarization.

Why Other Options Are Wrong:
Option (a) claims R explains A; incorrect because R is not universally true. Option (b) says both are true; but R is false in general. Option (d) claims A is false; electrostriction makes A true. “None of these” is unnecessary because (c) precisely fits.

Common Pitfalls:

• Equating electrostriction with piezoelectricity and assuming bidirectionality in all dielectrics.
• Forgetting the structural requirement (lack of inversion symmetry) for the converse effect.

Final Answer:
A is true but R is false