Heat

Form of energy which flow from one body to another body due to difference in temperature between the bodies.

Unit of heat: calorie

1 calorie=4.186 joule

Temperature: Physical cause which decided the direction of flow of heat.

Measurement of Temperature: Thermometer.

(c-0)/100 = (f-32)/180 = (k-273)/100

** freezing point of mercury is -39 C

**freezing point of alcohol is -115 C

Range of mercury thermometer -30 to 350 C

                Platinum                     -200 to 1200

                Thermocouple            -200 to 1500 

Specific heat Capacity: Amount of heat required to raise the temperature of unit mass of substance through 1C, Its SI unit is Joule/Kg Kelvin

 

** If in place of mass, one mole of gas is heated, the heat required to increase the temperature by unity called molecular heat capacity.

Specific Heat of Gas at constant Volume Sv

Specific Heat of Gas at Constant Pressure Sp

Molecular Heat capacity at Constant Volume Cv

Molecular Heat capacity at Constant Pressure Cp

Relation:

Cp/Cv =Sp/Sv =Y is adiabatic exponent of gas

Cp=MSp

Cv=MSv where M is the molar mass of gas.

Cp-Cv=R=M(Sp-Sv)

Sp-Sv=R/M

Thermal Expansion:  When a body is heated its length, area, and volume increases.

γ=2β=3α

** when temperature of eater increases from 0 to 4 C then, its volume decreases, if the temperature increases above $ C then, Its Volume start increasing.

Transmission of Heat:

• Conduction: heat is transformed by successive vibration of the particles of the medium without bodly movement of the particle. ex: heat transfer in solid.
• Convection: Heat is transformed by actual movement of particle, ex: liquid and gas.earth atmosphere is heated by convection.
• Radiation: Transfer of heat takes place with the speed of light, without affecting the intervening medium.

Newton Law of Cooling: The rate of loss of heat by body is directly proportional to the difference in temperature between the body and the surrounding.

Kirchoff's Law: The ratio of emissive power to absorptive power is same for all surfaces at the same temperature and is equal to emissive power of the black body at that temperature.

Stefan's Law: The radiant energy emitted by black body per unit area per unit time is directly proportional to the fourth power of its absolute temperature.

Change of State:

• Fusion: change from solid to liquid
• Freezing: liquid state to solid state, it takes place at fixed temperature.
• Vaporization: Change from liquid state to vapour state  Vaporization takes place by two method: Evaporation and Boiling.   Evaporation: It takes place only from the exposed surface of liquid at all temperature, it causes cooling.   Boiling: Takes Place at fixed temperature and from whole part of liquid, Boiling point of liquid increase with increase in pressure.
• Condensation: Change from vapor state to liquid state.
• Sublimation: change solid into vapor.it takes place when boiling point is less than melting point.
• Hoar frost: changes vapour into solid.

Latent Heat or Heat of Transformation: The amount of heat required to change unit mass of substance at constant temperature is called latent heat..

Q=mL( mass, latent heat)

Relative Humidity:

ratio of amount of water vapour present in a given volume of atmosphere to the amount of water vapour required to saturate the same volume at at temperature.

It is measure by hygrometer. It increases with increase in temperature.

Favourable atmosphere for human being:

temp 23 to 25 C

RH: 60 to 65%

Speed of air 0.75 miture/minute to 2.75.

Thermodynamics:

First law of Thermodynamics: heat energy given to the system is sued in following ways:

• Increasing the temperature and hence the internal energy of the system.
• Doing work by system

First law is equivalent to principal conservation of energy.

Isothermal Process: changes in system without changes in temperature.

Adiabatic Process: changes in system with there is no exchange of heat energy.

Second Law of Thermodynamics: 

kelvin statement: whole of the heat can never be converted into work

Clausis statement: heat by itself can't flow from body at lower temperature to body at higher temperature.

Heat Engine: Convert heat energy into mechanical energy.

It has three parts: souce, sink and working substance.

It may be divided into two types:

• Internal Combustion Engine: heat produced in engine itself ex: petrol engine, diesel engine.
• External Combustion Engine: heat produced outside the engine ex: steam engine.

Reversible/Carnot heat Engine: 

(η) = [Q1−Q2]Q1

Carnot Theorem: 

• All the reversible heat engine operating between same source and sink have same efficiency independent of nature of working substance.
• No heat engine operating between two given temp will have more efficiency than a reversible heat engine operating between the same two temp.

Refrigerator or Heat Pump:Vapour of freon CCL2F2 act as refrigerant.