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Why do liquid crystals change color with temperature?
The long, cigar shaped, molecules of a liquid crystal align themselves into orderly flat planes. The molecules in each flat plane are oriented at a slight angle from the molecules in the plane below it. Eventually, as the stack builds up and each layer is off set by a slight twisting from the one below it, two layers will have the same orientation. The distance between these two aligned layers is called the pitch. When white light is directed at this stack of molecules, the wavelength of light equal to this pitch distance is reflected back. At cold temperatures the pitch is far apart; red light is reflected back. At higher temperatures the molecules move faster and the layers twist more, causing the pitch to become shorter, reflecting blue light. Each liquid crystal has only a few degrees of temperature where the organization is such that light is reflected back. On either side of this temperature range, all light is absorbed and the liquid crystal appears black.
Reviews
Students can use Liquid Crystal Sheets to plan and conduct an investigation to describe and classify different kinds of materials by their observable properties.
Students can use Liquid Crystal Sheets to collect data to construct an argument with evidence that some changes caused by heating or cooling can be reversed and some cannot.
Students can use Liquid Crystal Sheets to make observations to provide evidence that energy can be transferred from place to place by heat currents.
Students can use Liquid Crystal Sheets s to apply scientific principles to design, construct, and test a device that either minimizes or maximizes thermal energy transfer.
Students can use Liquid Crystal Sheets for an investigation to determine the relationships among the energy transferred, the type of matter, the mass, and the change in the average kinetic energy of the particles as measured by the temperature of the sample.
The temperature is a measure of the average kinetic energy of particles of matter. The Liquid Crystal Sheets creates a beautiful thermal print when acted on by an object, such as your hand. Each color represents a different temperature.
Students can use Liquid Crystal Sheets to plan and conduct an investigation to provide evidence that the transfer of thermal energy when two components of different temperature are combined within a closed system results in a more uniform energy distribution among the components in the system (Second Law of Thermodynamics).
Students can place their hand on the Liquid Crystal Sheets to observe the transfer of heat energy to the surface of the temperature sensitive material. Each color represents a different temperature.
Each color represents a different temperature as students test a device that either minimizes or maximizes thermal energy transfer. There are three temperature ranges of sheets available for investigations.
Students can use the Liquid Crystal Sheets for an investigation to determine the relationships among the energy transferred by different objects.
* NGSS is a registered trademark of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of, and do not endorse, this product.
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