| Date | November 2011 | Marks available | 2 | Reference code | 11N.3.sl.TZ0.C4 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Explain | Question number | C4 | Adapted from | N/A |
Question
It was over a hundred years after the accidental discovery of liquid crystals that liquid-crystal displays (LCDs) came into common use in the 1990s. Liquid crystals are formed over a temperature range between the solid and the liquid state.
Describe the nematic liquid-crystal phase in terms of the arrangement of the molecules.
Explain the effect of increasing the temperature on the nematic liquid crystal.
Markscheme
no layered arrangement / molecules distributed randomly;
(on average) molecules point in same direction/orientation/directional order;
Accept suitable diagram.
directional order decreases/is lost / starts to behave like a liquid;
extra energy causes greater movement/overcomes intermolecular forces;
Examiners report
Very few of the candidates scored full marks on the description of the nematic liquid-crystal phase.
Probably because of the difficulty of selecting the correct words, and surprisingly only a few scored the mark in terms of the effect of the extra energy, namely causing greater movement or overcoming intermolecular forces.
