Which term refers to materials whose properties can be changed under external stimuli?

• A. Composite material
• B. Smart material
• C. Polymers
• D. Ceramic

Answer: (B)

Smart materials are materials whose properties can be changed or controlled by external stimuli such as temperature, electric or magnetic fields, light, or moisture. This ability to respond to environmental changes lets a design adapt during use, enabling sensing and actuation within a single material. Examples include shape memory alloys (like nitinol) that change shape with heat, electrochromic materials that alter color with voltage, and piezoelectric materials that shift dimensions or generate voltage when stressed. In contrast, a composite material is simply a combination of different substances to tailor properties, polymers cover a broad class with many non-responsive types, and ceramics are typically hard and brittle without intrinsic responsiveness. Thus, the term that refers to materials whose properties can be changed under external stimuli is smart material.