A nematic liquid crystal is a transparent or translucent liquid that causes the polarization (that is, the focusing in a plane) of light waves to change as the waves pass through the liquid. The extent of the change in polarization depends on the intensity of an applied electric field . Nematic comes from a Greek prefix nemato meaning threadlike and is used here because the molecules in the liquid align themselves into a threadlike shape. Nematic liquid crystals are used in twisted nematic display s, the most common form of liquid crystal display .
twisted nematic display (TN display)
A twisted nematic (TN) display is a common type...(WhatIs.com)
A typical nematic liquid crystal produces a 90-degree shift in the polarization of the light passing through when there is no electric field present. When a voltage is applied, an electric field is produced in the liquid, affecting the orientation of the molecule s. This causes the polarization shift to be reduced. The effect is slight at low voltages, and increases as the voltage (and the resulting field strength) increases. When the applied voltage reaches a certain level, the polarization shift disappears entirely.
Because their light transmission properties can be deliberately varied as a function of applied external voltage, nematic liquids are used in alphanumeric liquid-crystal displays ( LCD s), such as those found in digital wristwatches and many consumer electronic devices.