A liquid crystal thermometer or plastic strip thermometer is a type of thermometer that contains heat-sensitive (thermochromic) liquid crystals in a plastic strip that change color to indicate different temperatures. The thermometer is a device that measures Temperature or Temperature gradient using a variety of different principles it comes from the Greek roots Thermochromism is the ability of Substance to change Color due to a change in Temperature. Liquid crystals are substances that exhibit a phase of matter that has properties between those of a conventional Liquid, and those of a Solid Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature  Liquid crystals possess the mechanical properties of a liquid, but have the optical properties of a single crystal. Temperature changes can affect the color of a liquid crystal, which makes them useful for temperature measurement. The resolution of liquid crystal sensors is in the 0. 1°C range. The Celsius Temperature scale was previously known as the centigrade scale. Disposable liquid crystal thermometers have been developed for home and medical use.
There are two stages in the liquid crystals, 1 - the hot nematic stage is the closest to the liquid phase where the molecules are freely moving around and only partly ordered. 2 - the cold smectic stage is closest to the solid phase where the molecules align themselves into tightly wound chiral matrixes.
Liquid crystal thermometers portray temperatures as colors and can be used to follow temperature changes caused by heat flow. They can be used to observe that heat flows by conduction, convection, and radiation. Heat conduction or thermal conduction is the spontaneous transfer of thermal energy through matter from a region of higher Temperature to a region of lower Convection in the most general terms refers to the movement of molecules within Fluids (i Radiation, as in Physics, is Energy in the form of waves or moving Subatomic particles emitted by an atom or other body as it changes from a higher energy
Liquid crystals are very often used when someone is ill and for other medical reasons. They read body temperature by being placed against the forehead. Liquid crystals are safer than a mercury-in-glass thermometer, but don't always give an exact result, especially the smaller ones. A mercury-in-glass thermometer, invented by German physicist Daniel Gabriel Fahrenheit, is a Thermometer consisting of mercury in a Glass
Liquid crystal thermometers are also commonly used in aquariums. An aquarium (plural aquariums or aquaria) is a Vivarium consisting of at least one transparent side in which Water -dwelling Plants 
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