Hysteresis is defined as what phenomenon?

• A. A change in temperature that causes the reversible hydrocolloid to transform from one physical state to another
• B. Absorption of water causing swelling
• C. Loss of water causing shrinkage
• D. A color change under light exposure

Answer: (A)

Hysteresis is the idea that a material’s state depends on its thermal history, so its transitions between states occur at different temperatures depending on whether you’re heating or cooling. For a reversible hydrocolloid like agar, it gels when cooled and liquefies when heated, but the gel-to-liquid transition happens at a different temperature than the liquid-to-gel transition. A temperature change that causes the material to switch between physical states captures this temperature-driven, history-dependent behavior. The other options describe swelling, shrinking, or color change, which aren’t about this temperature-dependent state change.