Rory Compton, of Balclutha Primary School, asks :-

What is a liquid crystal display?

Ken Jolley, a chemist at Massey University, responded.

Liquid crystal displays can be attached to electronic devices such as calculators, watches and television sets so that numbers, letters and even pictures can be displayed. But how do they work?

Consider one of the display characters on an electronic calculator. This consists of seven very thin glass wafers containing liquid crystal. The glass wafers are placed on a black background and arranged in the form of a figure eight. The liquid crystal is a special type of liquid that is made up of long thin molecules shaped a bit like lollipop sticks but much smaller. The molecules like to line up alongside each other, rather like matches in a matchbox. When the molecules are arranged in this way light can pass through the wafer and you can see the black line behind it. If a voltage is applied across the wafer the molecules turn through right angles and when this happens light cannot pass through the wafer and the black line cannot be seen. Thus, if a voltage is applied to all seven wafers no figure will be displayed. If a voltage is applied only to the central wafer a black zero will appear. By selecting various combination of wafers any number from 0 to 9 can be displayed.

Liquid crystal displays require the skills of chemists to make the special molecules that make up a liquid crystal and the skills of physicists who make the clever electronic devices that turn the wafers on and off.