L3 - Heat Work and FirstLaw(1)

# L3 - Heat Work and FirstLaw(1) - PH2103 Thermal Physics...

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PH2103 Thermal Physics Lecture 3: Heat and Work Massimo Pia Ciamarra [email protected] SPMS-PAP-03-14 Textbook paragraph: 1.4

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1. Energy and thermodynamics Internal energy Mechanical Equivalent of Heat 2. First law of thermodynamics Heat and Internal energy Conservation of energy 3. Heat Transfer Conduction Convection Radiation Agenda
1. Energy and thermodynamics Internal energy & Heat

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Pressure of an Ideal Gas __ 2 2 1 3 2 v m V N P
Pressure can be increased by Increasing the number of molecules per unit volume in the container www.pitt.edu Pressure of an Ideal Gas __ 2 2 1 3 2 v m V N P

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Pressure can be increased by Increasing the number of molecules per unit volume in the container Increasing the average translational kinetic energy of the molecules www.pitt.edu Pressure of an Ideal Gas __ 2 2 1 3 2 v m V N P
Molecular Interpretation of Temperature The total kinetic energy (N molecules) is proportional to the absolute temperature : P = 2 3 ( N V )( 1 2 m v 2 ) PV = Nk B T = nRT } 1 2 m v 2 = 3 2 k B T KE tot = N ( 1 2 m v 2 ) = 3 2 Nk B T = 3 2 nRT

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Internal Energy In an ideal gas, the KE is the only type of energy the molecules can have U is the internal energy of the gas 3 2 U nRT
Internal Energy In an ideal gas, the KE is the only type of energy the molecules can have U is the internal energy of the gas In a polyatomic gas, additional possibilities for contributions to the internal energy are rotational and vibrational energy in the molecules 3 2 U nRT

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Heat Heat is the transfer of energy between two objects in thermal contact because of a temperature difference between them Denoted by the symbol Q bakoheat.com SI unit: Joule Historically, unit of heat was “calorie” (cal), energy necessary to raise 1 g of water from 14.5 o C to 15.5 o C 1 cal = 4.186 J ( mechanical equivalent of heat ) Cal = kcal = 1000 cal
Mechanical Equivalent of Heat Joule established the equivalence between mechanical energy and internal energy It takes approximately 4.18 J of mechanical energy to raise 1 g of water by 1 o C James Prescott Joule (1818- 1889) was an English physicist and brewer

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Joule’s Experiment Both heat and work can change the internal energy of the system
Joule’s Experiment Work is done on water . Energy is transferred to water and appears as an increase in temperature Both heat and work can change the internal energy of the system

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Joule’s Experiment Work is done on water . Energy is transferred to water and appears as an increase in temperature We could replace the insulating walls by conducting walls and transfer heat to the system to produce the same increase in temperature Both heat and work can change the internal energy of the system
Joule’s Experiment Work is done on water . Energy is transferred to

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