HAPTER LEVEN - NCERT

CHAPTER ELEVENTHERMAL PROPERTIES OF INTRODUCTIONWe all have common sense notions of heat and is a measure of hotness of a body. A kettlewith boiling water is hotter than a box containing ice. Inphysics, we need to define the notion of heat, temperature,etc., more carefully. In this chapter, you will learn what heatis and how it is measured, and study the various proceses bywhich heat flows from one body to another. Along the way,you will find out why blacksmiths heat the iron ring beforefitting on the rim of a wooden wheel of a horse cart and whythe wind at the beach often reverses direction after the sungoes down. You will also learn what happens when water boilsor freezes, and its temperature does not change during theseprocesses even though a great deal of heat is flowing into orout of TEMPERATURE AND HEATWe can begin studying thermal properties of matter withdefinitions of temperature and heat. Temperature is a relativemeasure, or indication of hotness or coldness.

volume expansion (Fig. 11.5). Fig. 11.5 Thermal Expansion. If the substance is in the form of a long rod, then for small change in temperature, ∆T, the fractional change in length, ∆l/l, is directly proportional to ∆T. ∆ ∆ l l =α1 T (11.4) where α 1 is known as the coefficient of linear expansion (or linear expansivity) and is

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  Thermal, Expansion, Thermal expansion

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