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- 1. flipperworks.com Applications• Engineering• Chemistry• Earth Science• Astrophysics• Everyday life
- 2. flipperworks.comApplications To design pressure cookers
- 3. flipperworks.com
- 4. flipperworks.com
- 5. flipperworks.comApplications Automobile engine
- 6. flipperworks.comApplications
- 7. flipperworks.comApplications Household refrigerator
- 8. Power Plant flipperworks.comApplications
- 9. flipperworks.comApplications Solar Heater
- 10. flipperworks.com1 Introduction • In the study of thermal physics there is a need to approach it in two levels. – macroscopic level – microscopic level
- 11. flipperworks.com1 Introduction Macroscopic Approach • Look at macroscopic variables that can be measured by simple experiments: – temperature – pressure – volume • Derive general relationships and equations that can describe the experiments. – Advantage: • easily related to experiment – Disadvantage: • lacks fundamental explanations
- 12. flipperworks.com1 Introduction Microscopic Approach • Explain macroscopic properties by looking closely into the atoms and molecules that make up matter to understand what is happening . – Advantage: • Gives a real explanation of what is actually happening. – Disadvantage: • Too many particles will require the use of complex computation.
- 13. flipperworks.com1 Introduction • Lets begin by asking ourselves, – What is Temperature? – What is Heat?
- 14. flipperworks.com2. Temperature • In a macroscopic view: – Temperature is the physical property which determines the direction flow of heat. heat • e.g Heat flows from higher temperature to lower temperature Hot Cold Heat flows
- 15. flipperworks.com2. Temperature • In a macroscopic view: – Temperature is a physical property of a system that provide a measure of hotness or coldness.
- 16. flipperworks.com2. Temperature • In a microscopic view: – Temperature is a measure of the average kinetic energy of molecules in a body.
- 17. flipperworks.com2.1 Heat and Thermal Equilibrium • When two bodies are in thermal contact, energy can be transferred between them. Hot Cold
- 18. flipperworks.com2.1 Heat and Thermal Equilibrium • Microscopically the energy transfer occurs in two ways. Higher kinetic Lower kinetic energy molecules energy molecules Hot Cold
- 19. flipperworks.com2.1 Heat and Thermal Equilibrium • But the rate of transfer of energy from a hotter body is always greater than that from a cooler body. Higher kinetic Lower kinetic energy molecules energy molecules Hot Cold Energy Energy
- 20. flipperworks.com2.1 Heat and Thermal Equilibrium • This net energy transfer from a body of a higher temperature to a lower temperature is known as heat. Hot Cold Heat flows
- 21. flipperworks.com2.1 Heat and Thermal Equilibrium • Heat will flow between two bodies as long as there is temperature difference between them. Hot Cold Heat flows
- 22. flipperworks.com2.1 Heat and Thermal Equilibrium • When two bodies are in thermal contact and there is no flow of heat from one body to another, they are said to be in thermal equilibrium. • At thermal equilibrium (microscopically) The rate of transfer of energy is the same from both bodies. Thus these two bodies are said to be at the same temperature.
- 23. flipperworks.com2.1 Heat and Thermal EquilibriumConsider the 2 systems, X and Y: insulator No thermal contact No flow of heat between X and Y X Y Fig 1
- 24. flipperworks.com2.1 Heat and Thermal Equilibrium X and Y are in thermal contact Temperature of X > Temperature of Y Rate of transfer of energy from X to Y > Rate of transfer of energy from Y to X X Y Heat flows from X to Y Fig 2 heat Temperature of X decreases and Temperature of Y increases
- 25. flipperworks.com2.1 Heat and Thermal Equilibrium X and Y in thermal equilibrium Rate of transfer of energy from X to Y = Rate of transfer of energy from Y to X X Y No flow of heat between X and Y Fig 3 Temperature of X = Temperature of Y
- 26. flipperworks.com2.2 Zeroth Law (law of thermal equilibrium) Zeroth law of thermodynamics states that if bodies A and B are in thermal equilibrium with a third body C, then A and B are in thermal equilibrium with each other. C A ⇒ TA = TB C B TA = T C TB = TC
- 27. flipperworks.com2.2 Zeroth Law (law of thermal equilibrium) • The significance of the Zeroth Law: – It allows us to claim that two objects in thermal equilibrium with each other must be at the same temperature. – It allows us to know whether objects are at the same temperature, even when we can’t place them in thermal contact. – It allows temperature to become reproducible, and quantifiable. (Temperature can be a physical quantity)
- 28. flipperworks.com2.2 Zeroth Law (law of thermal equilibrium) In other words We could create a thermometer to measure temperature.
- 29. flipperworks.comExample 1 A solid X is in thermal equilibrium with a solid Y, which is at the same temperature as a third solid Z. The three bodies are of different materials and masses. Which one of the following statements is certainly true? A X and Y have the same heat capacity. B There is no net transfer of energy if X is placed in thermal contact with Z. C It is not necessary that Y should be in thermal equilibrium with Z. D It is not necessary that X should be at the same temperature as Z.Tx = Ty Therefore Tx = Tz Ans: BTy = Tz
- 30. flipperworks.com2.3 Thermodynamic Temperature Scale • To measure temperature quantitatively, we need to have a scale. Empirical Scale 2 Scales Thermodynamic Temperature Scale • An empirical temperature scale is a temperature scale based on experimental results. – e.g. Centigrade Scale
- 31. flipperworks.com2.3 Thermodynamic Temperature Scale • An empirical scale requires a thermometric property and two fixed points (i.e ice point and steam point) • Thermometric Property: A physical property that changes in a known way with temperature.
- 32. flipperworks.com2.3 Thermodynamic Temperature Scale Examples of thermometric properties used in various thermometers: Type of Thermometer Thermometric Property liquid-in-glass length of mercury in a thermometer capillary tube Resistance resistance of platinum wire thermometer Thermocouple EMF of a copper- thermometer constantan thermocouple constant volume gas pressure of a fixed mass thermometer of gas at constant volume
- 33. flipperworks.comThermomete Constant volume gas thermometerrs Thermocouple Resistance Thermometers mV iron iron constantan Junction 2 Junction 1
- 34. flipperworks.com2.3 Thermodynamic Temperature Scale • Problem with empirical scales based on particular thermometers: – scales agree only at calibration points. Ideal • A need to have a scale which is independent of any thermometric property (absolute scale). – reliable – reproducible
- 35. flipperworks.com2.3 Thermodynamic Temperature Scale • The THERMODYNAMIC temperature scale is theoretical and is independent of the properties of any particular thermometric substance. • The scale is also known as the Absolute Temperature Scale.
- 36. flipperworks.com2.3 Thermodynamic Temperature Scale The two fixed points in the Thermodynamic Temperature Scale are: (a) absolute zero which is the temperature at which the pressure of an ideal gas becomes zero. It is arbitrarily given the value 0 K. (b) the triple point of water which is the temperature at which ice, water and water vapour coexist in dynamic equilibrium.
- 37. flipperworks.com2.3 Thermodynamic Temperature Scale Phase diagram for water
- 38. flipperworks.com2.3 Thermodynamic Temperature Scale Diagram of a triple point cell Thermometer well Water Dewar vapour vessel Ice Ice water sheath mixture Thermal contact liquid Water
- 39. flipperworks.com2.3 Thermodynamic Temperature Scale • The triple point of water is chosen because it – is unique, invariant and occurs only at one definite temperature and pressure. (T = 273.16 K and Pressure = 611.73 Pa) – can be easily and accurately reproduced using a triple point cell.
- 40. flipperworks.com2.3 Thermodynamic Temperature Scale The unit of temperature in the thermodynamic scale is the kelvin, symbol K. Kelvin is also the S.I. unit of temperatureOne kelvin is defined to be 1 of the 273.16thermodynamic temperature of the triple point of water 1 If, × Ttr = 1 K 273.16 Ttr = 273.16 K
- 41. flipperworks.com2.4 The Celsius ScaleThe Celsius scale is related to the Thermodynamicscale by the exact equation: t/oC = T/K – 273.15 The unit for this scale is degree Celsius, symbol oC (same symbol as for degree Centigrade).
- 42. flipperworks.comExample 2 What is the change in temperature in kelvin when the temperature falls from 540.85 °C to 502.02 °C? A 38.83 K B 311.98 K C 273.15 K D 228.85 K Ans: A
- 43. flipperworks.comWhat we have covered• Definition of Temperature – Macroscopic – Microscopic• Heat and Thermal Equilibrium• Zeroth Law and its significance – Thermodynamic Temperature Scale – Celsius Scale
- 44. flipperworks.com What happen when you heat a substance?ExpandsTemperature increase
- 45. flipperworks.com3 Heat Capacity Heat Capacity HEAT CAPACITY, C, of a body is defined as the quantity of heat absorbed / liberated, Q, by the body per unit temperature change. Q = C ∆θ S.I. unit for heat capacity is J K-1
- 46. flipperworks.com3 Heat Capacity Specific Heat Capacity SPECIFIC HEAT CAPACITY, c, of a material, is defined as the quantity of heat absorbed / liberated, Q, per unit mass of the material per unit temperature change. Q = m c ∆θ The S.I. unit of specific heat capacity is J kg-1 K-1 C = mc
- 47. flipperworks.comExample 3The specific heat capacity of copper is 400 J kg -1 K-1.(a) What is the heat capacity of 5 kg of copper?(b) If the copper temperature rises by 10 oC, what would be the heat gained? (a) heat capacity C = m c = 5 x 400 = 2,000 J K-1
- 48. flipperworks.comExample 3The specific heat capacity of copper is 400 J kg -1 K-1.(a) What is the heat capacity of 5 kg of copper?(b) If the copper temperature rises by 10 oC, what would be the heat gained? (b)Heat gained, Q = m c ∆θ = 5 x 400 x 10 = 20,000 J
- 49. flipperworks.com3.1.1 Determination of specific heat capacity, c (Electrical Method) For Solid Conductors: (Insulation)
- 50. flipperworks.comBy the principle of conservation of energy,Assuming negligible heat loss to the surroundings.Electrical energy supplied = Heat absorbed by block VIt = m c (θ2 - θ1) V It c= m(θ 2 − θ1 ) What happens to the value of c if heat loss is not negligible?
- 51. flipperworks.comBy the principle of conservation of energy,Assuming negligible heat loss to the surroundings.Electrical energy supplied = Heat absorbed by block V I t2 = m cL (θ2 - θ1) + h t2 t2 would be longer than t (ideal time taken) cL = V It 2 m(θ 2 − θ1 ) The calculated cL will be higher than the actual value c.

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