Describe the meaning of the term liquid crystals.

When a liquid-crystal display is warmed with a hairdryer, the display loses its clarity and may no longer be visible. Explain why this happens on a molecular level.

fluids that have physical properties dependent on molecular orientation/orderly molecular arrangement;

Allow “fluids that exhibit molecular orientation/orderly molecular arrangement”.

Allow “(LCs) show properties of liquids and crystals simultaneously”.

thermal agitation disrupts directional order of liquid crystal / OWTTE;

rotation of plane polarized light disrupted / crystals no longer have ability to affect light in same way / OWTTE;

An understanding of liquid crystals was generally conveyed. Some candidates stated that liquid crystals show properties of liquids and solids simultaneously which did not score as they did not mention the crystalline state explicitly for solids. In (b) only the really top-tier candidates were able to explain the question asked on a molecular level, i.e. the fact that thermal agitation disrupts the directional order of the liquid crystal and as a result the rotation of plane polarized light is disrupted. This question proved to be possibly one of the hardest questions on the paper overall for candidates.

An understanding of liquid crystals was generally conveyed. Some candidates stated that liquid crystals show properties of liquids and solids simultaneously which did not score as they did not mention the crystalline state explicitly for solids. In (b) only the really top-tier candidates were able to explain the question asked on a molecular level, i.e. the fact that thermal agitation disrupts the directional order of the liquid crystal and as a result the rotation of plane polarized light is disrupted. This question proved to be possibly one of the hardest questions on the paper overall for candidates.