General physics-i 18
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This chapter discusses concepts of thermodynamics including temperature, heat, work, and heat capacity. It introduces the three laws of thermodynamics: 1) Zeroth law: two objects in thermal equilibrium with a third object are in equilibrium with each other 2) First law: the change in internal energy of a system is equal to the heat supplied minus the work done by the system 3) Applications of thermodynamic processes including adiabatic, constant-volume, cyclical, and free expansion processes. Modes of heat transfer - conduction, convection, and radiation - are also covered.
![18-2 Temperature
Thermodynamics
=Thermal physics
Temperature
Hot? Cold?
Scale?
Kelvin (K) in SI unit
[273 + Celsius]
Universe was very hot right
after Big Bang(1039 K)
Now about (3K)](https://image.slidesharecdn.com/general-physics-i18-141002140024-phpapp02/85/General-physics-i-18-3-320.jpg)
![Cyclical process = [Q=W]
Returns to the same state:
If the system received a
certain amount of heat,
the same amount of work
has been done by the
system.
Internal energy remains
the same after a cycle.](https://image.slidesharecdn.com/general-physics-i18-141002140024-phpapp02/85/General-physics-i-18-21-320.jpg)
![Free expansion = [pext=0:W=0]
No heat transfer.
No external pressure.
No work in expansion.
No equilibrium during
the expansion](https://image.slidesharecdn.com/general-physics-i18-141002140024-phpapp02/85/General-physics-i-18-23-320.jpg)
General physics-i 18
- 1. Chapter 18 Temperature, Heat, and the First Law of Thermodynamics
- 2. Things to learn ƒ We will learn concepts useful in thermodynamics (temperature, heat, work, and heat capacity) and relations among them. ƒ We will learn laws of thermodynamics and their applications: - Zeroth law: T equal at thermal equilibrium - First law: energy conservation - Adiabatic, constant-volume, cyclical, free-expansion processes. ƒ We will learn effects of heat: - Change in T - Change of phase (heat of transformation) - Thermal expansion ƒ We will learn modes of heat transfer.
- 3. 18-2 Temperature Thermodynamics =Thermal physics Temperature Hot? Cold? Scale? Kelvin (K) in SI unit [273 + Celsius] Universe was very hot right after Big Bang(1039 K) Now about (3K)
- 4. 18-3 The zeroth Law of Thermodynamics If bodies A and B are each in thermal equilibrium with a third body T, then they are in thermal equilibrium with each other.
- 5. 18-4 Measuring temperature Practical standard 0 degrees Celsius : freezing point of water 100 degrees Celsius : boiling point of water Easily reproducible; these may vary! Scientific reference scale T of Triple-point of water is defined by 273.16 K International agreement reproducible
- 6. Calibrating thermometers Triple-point of water = vapor, water, and ice are in equilibrium (273.16 K) Make a gas thermometer in equilibrium with a triple-point water cell which has a definite temperature
- 7. Constant-volume gas thermometer Use the fact: T= C p T: temperature C: constant if the volume of a gas is fixed P: pressure
- 8. Constant-volume gas thermometer gives correct value as p3 Æ 0
- 9. 18-5 Celsius & Fahrenheit
- 10. 18-6 Thermal expansion ƒ Thermal expansions -Expansion slots for sections of the bridge -Dental cavity filling: thermal expansion property should be matched. -Bimetal strip ƒ Linear expansion ƒ Volume expansion
- 11. SP 18-2 ƒ A oil trucker loaded 37,000 L of diesel fuel in Las Vegas and delivered his entire load in Payson, UT (23 oC lower). ƒ β of diesel fuel = 9.5 × 10-4 /oC ƒ α of steel truck tank = 11 × 10-6 /oC ƒ How many liters did he deliver?
- 12. 18-7 Temperature and Heat Heat is the energy transferred between system and environment because of the temperature difference a) System is hotter than environment Æ System loses heat (Q<0) b) Same temperature (in equilibrium) Æ No heat flows (Q=0) c) System is colder than environment Æ System gains heat (Q>0)
- 13. 18-8 The absorption of heat by solids and liquids
- 14. ƒ Heat Capacity C ƒ Specific Heat (heat capacity per unit mass) ƒ Molar Specific Heat (heat capacity per one mole) • 1 mol = 6.02 X 1023 ƒ An important point: • constant pressure vs. constant volume ƒ Heat of Transformation - Heat of vaporization - Lv=539 cal/g = 40.7 kJ/mol = 2256 kJ/kg (water) - Heat of fusion - LF=79.5 cal/g = 6.01 kJ/mol = 333 kJ/kg (water)
- 15. Molar Specific Heat Problem 23
- 16. SP 18-3
- 17. 18-9 A closer look at Heat and Work
- 18. P-V plot
- 19. Problem 43
- 20. 18-10 The first law of Thermodynamics 18-11 Special cases Adiabatic process: no heat transfer Constant volume process: no work
- 21. Cyclical process = [Q=W] Returns to the same state: If the system received a certain amount of heat, the same amount of work has been done by the system. Internal energy remains the same after a cycle.
- 22. Problem 48 cyclic process
- 23. Free expansion = [pext=0:W=0] No heat transfer. No external pressure. No work in expansion. No equilibrium during the expansion
- 24. SP 18-5 Boiling water Æ steam Constant pressure (1atm) Work done by the gas?
- 25. 18-12 Heat Transfer Mechanisms: conduction Problem 61
- 26. Conduction through a composite slab P must be invariant (energy conservation) Parallel combination:P=P1+P2 energy is transferred through two channels
- 27. Convection Difference in temperature Æ Difference in pressure Æ Fluid can flow (from high pressure to low pressure) Æ Heat is transferred
- 28. Radiation Electromagnetic wave e.g. radiation from the Sun Any object with T > 0 K radiates!
- 29. SP 18-7 ƒ Ts = -23 oC; Ta = + 6.0 oC Water: m = 4.5 g, A = 9.0 cm2, d = 5.0 mm ε = 0.90 ƒ Find the time required for the water to freeze via radiation. Can the freezing be accomplished during one night?