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( Relaxation time)
Relaxation time is a general concept in physics for the characteristic time in which a system changes to an equilibrium condition from a non-equilibrium condition. It can measure the time-dependent response of a system to well-defined external stimuli. For instance, the properties of a dielectric change on a time scale determined by the relaxation time when an external electric field is changed. This so-called dielectric relaxation time is a property of a solid that is closely related to its conductivity. The dielectric relaxation time is a measure of the time it takes for charge in a semiconductor to become neutralized by conduction process. It is small in metals and can be large in semiconductors and insulators. An amorphous solid, such as amorphous indomethacin displays a temperature dependence of molecular motion, which can be quantified as the average relaxation time for the solid in a metastable supercooled liquid or glass to approach the molecular motion characteristic of a crystal. Differential scanning calorimetry can be used to quantify enthalpy change due to molecular structural relaxation[1]. Let the homogenous differential equation  model damped unforced oscillations of a weight on a spring.
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