| Date | November 2014 | Marks available | 1 | Reference code | 14N.3.hl.TZ0.12 |
| Level | HL | Paper | 3 | Time zone | TZ0 |
| Command term | Describe | Question number | 12 | Adapted from | N/A |
Question
Liquid crystals are widely used in displays.
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.
Markscheme
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;
Examiners report
There were good descriptions of liquid crystals and many understood the thermal change in (b). The aspect of Kevlar® allowing it to be used as a liquid crystal was better known than that for bullet-proof jackets. Candidates needed to recognize the strong hydrogen bonding between chains.
There were good descriptions of liquid crystals and many understood the thermal change in (b). The aspect of Kevlar® allowing it to be used as a liquid crystal was better known than that for bullet-proof jackets. Candidates needed to recognize the strong hydrogen bonding between chains.
