Heat and thermodynamics Part-I

Heat and thermodynamics-Part-1 : By R.Buvana Heat and thermodynamics-Part-1

Heat and thermodynamics-Part-I : Heat and thermodynamics-Part-I 1.Heat and temperature 2.Thermometry and temperature scales 3.Absolute temperature 4.Thermal Expansion and their applications 5.Home work questions.

Heat : Heat Heat is something that produces the sensation of hotness or coldness in us. Thus heat is a form of energy that produces the sensation of hotness or coldness in us. Heat energy and Kinetic theory of matter Heat energy flows from a hot body to a cold body. Sign conventions-Heat gained by a body is taken as positive while heat lost by a body is taken as negative.

Units of heat : Units of heat In SI unit of heat is joule(J) In CGS unit of heat is calorie. It is written as cal. Bigger units of heat are kilocalorie (kcal) and kilojoules(kJ). 1 k cal=1000cal 1kJ=1000J.

Temperature : Temperature Temperature of a substance is a physical quantity which measures the degree of hotness or coldness of the substance. Thus, temperature of a substances is the measure of the average kinetic energy of its molecule.

Thermometry : Thermometry A branch of science which deal s with the measurement of temperature of a substance is known thermometry. A device used to measure the temperature of a body is called thermometer. A substance that exhibits one of these thermometric properties and used in a thermometer is called a thermometric substance.

Temperature scales : Temperature scales To measure the temperature of a body with the help of a thermometer, different temperature scales are defined by which a thermometer can be calibrated. Each temperature scale has two fixed points known as lower fixed point and upper fixed point. The various temperature scales used to calibrate a thermometer are-

Conti… : Conti… 1.Celsius Scale(°C). In the Celsius scale 0° C is the lower fixed point and 100°C is the upper fixed point. 2.Fahrenheit Scale (°F).In the Fahrenheit scale 32°F is the lower fixed point and 212°F is the upper fixed point. 3.Reaumer Scale( °R). ). In the Celsius scale 0° R is the lower fixed point and 80°R is the upper fixed point. The formula for the conversion of one temperature scale into another is given below C-0/100=F-32/180=R-0/80 where C,F,R denote the temperature of a body on Celsius, Fahrenheit and Reaumer scales of temp. respectively.

Absolute scale or Kelvin scale : Absolute scale or Kelvin scale The variation of pressure with temperature e for different amount of a given gas in the bulb of a constant volume thermometer .The scale of temp. whose zero coincides with -273.15°C is known as absolute scale or Kelvin scale of temperature. The zero of absolute scale of temperature is denoted by 0 K and known as absolute zero. T(K)=?(°C)+273.15

Thermal expansion : Thermal expansion Almost all solids, liquids and gases expand when their temperature increases. The increase of size of a body due to the increase in the temperature is called thermal expansion. Three types of expansions can take place in solids namely linear, superficial and cubical expansions. Linear Expansion-When a solid is heated and its length increases, then the expansion is called linear expansion. L=L0(1+a?)

Conti… : Conti… Where a is called the coefficient of linear expansion. Superficial expansion-When a solid is heated and its area increases, then the thermal expansion is called superficial or area expansion. A=A0(1+ß?)where ß is called the coefficient of area expansion. Volume expansion-When a substance is heated and its volume increases, then the expansion is called volume expansion . V=V0(1+??)where ? is called coefficient volume expansion .

Relation between a,ß,? : Relation between a,ß,? ß=2a ?=3a Variation of density with temperature ??=?0(1-??) Where ?0 is initial density and ?? final density ? is change in temperature

Home work questions : Home work questions 1.How the fishes can survive in the extreme winter when ponds and lakes are frozen? 2.Calculate the temperature whose value is the same on the Celsius and Fahrenheit scale? 3.What is a bimetallic strip? 4.What is the lowest possible temperature?