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Section 1 Notes: Temperature Scales and Conversions 1. How does a thermometer determine temperature?

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Presentation on theme: "Section 1 Notes: Temperature Scales and Conversions 1. How does a thermometer determine temperature?"— Presentation transcript:

1 Section 1 Notes: Temperature Scales and Conversions 1. How does a thermometer determine temperature?

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3 Thermodynamics (Unit 1 spring)

4 Thermodynamics- Physics that deals with heat and its conversion into other forms of energy.

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6 Temperature Variables T K = Temperature Kelvin T C = Temperature Celsius T F = Temperature Fahrenheit

7 Absolute Zero= 0 Kelvin, a temperature where no motion would occur. There is no kinetic energy in the molecules. 0 Kelvin= ºCelsius

8 Conversion Scale ( )

9 Example 1 A healthy person has an oral temperature of 98.6 ºF. What would this reading be on the Celsius scale?

10 Example 1 A healthy person has an oral temperature of 98.6 ºF. What would this reading be on the Celsius scale?

11 Example 2 A time and temperature sign on a bank indicates the outdoor temperature is ºC. What is the corresponding temperature on the Fahrenheit scale?

12 Example 2 A time and temperature sign on a blank indicates the outdoor temperature is ºC. What is the corresponding temperature on the Fahrenheit scale?

13 The Kelvin Temperature Scale Has scientific significance due to its absolute zero point. Has equal divisions as the Celsius scale Not written in degrees 0 º C is K Therefore the conversion is:

14 Intro 1. Convert 50º F into ºC and Kelvin

15 Intro 1. Convert 50º F into ºC and Kelvin

16 Intro 1. Convert 50º F into ºC and Kelvin

17 Section 2 Notes: Kinetic Energy and Temperature Kinetic energy (KE)- Energy of movement Temperature- A measure proportional to the average kinetic energy of a substance. –higher temperature = higher kinetic energy –The more kinetic energy the quicker the molecules are moving around

18 Click on the diagram to be taken to the page

19 Draw a picture representing molecular motion of three identical molecules at these two temperatures

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21 Section 3 Notes: Internal Energy vs. Heat Internal energy (U)- Sum of the molecular energy –kinetic energy, potential energy, and all other energies in the molecules of a substance. –Unit: Joule Heat (Q) is energy in transit –energy flows from a hot to a cold substance. –Unit: Joule An object never has “heat” or “work” only internal energy (heat is transferred and work is done)

22 Heat is energy in transit Heat lost by one object equals heat gained by another Heat lost = Heat gained -Q A = Q B

23 Heat transfers from hot to cold (a)Holding a hot cup (b)Holing a cold glass (heat leaving your hand feels cold)

24 The coffee looses 468J of heat. How much heat does Bob gain? (assuming no heat was lost to the surroundings) The same: Bob gained 468 J of heat Example 3

25 –Direction: From high temperature to low temperature –Rate of transfer depends on temperature difference: The greater temperature difference the greater the energy transfer T water = 20º C T can = 15º C T water = 35º C T can = 5º C

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27 Example 4 Where would the greater energy transfer take place and which way would the energy transfer? A.Ice = 0 ºC Juice = 20 ºC B.Ice = 0 ºC Juice = 25 ºC B. has a bigger temperature difference and therefore greater energy transfer. Energy transfers from hot to cold: Juice to Ice

28 What happens when the temperature inside and out are equal? T water = 11º C T can = 11º C

29 Heat is transferred until there is thermal equilibrium Thermal Equilibrium- When temperatures are equal and there is an even exchange of heat T water = 11º C T can = 11º C

30 Section 4 Notes: Heat Transfer Types of Heat Transfer: –Conduction –Convection –Radiation

31 Conduction- Caused by vibrating molecules transferring their energy to nearby molecules. Not an actual flow of molecules. heat transfer

32 Thermal conductors- rapidly transfer energy as heat Thermal insulators- slowly transfer energy as heat

33 Challenge Put the following in order of most thermally conductive to least. Copper, Wood, Air, Water, Concrete

34 1. Copper 2 Concrete 3. Water 4. Wood 5. Air

35 Convection- process in which heat is carried from place to place by the bulk movement of a fluid (gas or liquid). Examples

36 Radiation (electromagnetic radiation) – Reduce internal energy by giving off electromagnetic radiation of particular wavelengths or heated by an absorption of wavelengths. Ex. The UV radiation from the sun making something hot. Absorption depends on the material.

37 Draw your own pictures in the table that represent these three types of heat transfer.

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39 Section 5: Laws of Thermodynamics

40 A System System- A collection of objects upon which attention is being focused on. This system includes the flask, water and steam, balloon, and flame. Surroundings- everything else in the environment The system and surrounding are separated by walls of some kind. System Surroundings

41 Walls between a system and the outside Adiabatic walls- perfectly insulating walls. No heat flow between system and surroundings.

42 In a system: How can you measure the quantity of heat entering or leaving? Q = Δ UorQ = U f – U 0 Q: The quantity of heat that enters or leaves a system U 0 : Initial internal energy in system U f : Final internal energy in system If Q is positive then energy entered the system If Q is negative then energy left the system This is directly related to temperature. –If the system gets colder then heat left –If the system gets warmer then heat entered

43 Example 5 The internal energy of the substance is 50 J before The internal energy of the substance is 145 J after a) How much heat was transferred in this system? b) Did it enter or leave?

44 First Law of Thermodynamics: –Conservation of energy applied to thermal systems. –Energy can neither be created nor destroyed. It can only change forms –Stated in an equation ΔU = Q + W

45 First Law of Thermodynamics: Conservation of Energy ΔU = Q + W –Internal Energy (U) (positive if internal energy is gained) –Heat (Q) (positive if heat is transferred in) –Work (W) (positive if work is done on the system) –The unit for all of these is the Joule (J)

46 Example 6 & 7 6. A system gains 1500 J of heat from its surroundings, and 2200 J of work is done by the system on the surroundings. What is the change in internal energy? 7. A system gains 1500 of heat, but 2200 J of work is done on the system by the surroundings. What is the change in internal energy?

47 6. A system gains 1500 J of heat from its surroundings, and 2200 J of work is done by the system on the surroundings. What is the change in internal energy? 7. A system gains 1500 of heat, but 2200 J of work is done on the system by the surroundings. What is the change in internal energy? Example 6 & 7

48 Now how can you tell if work is done by or on a system? Is work done on or by the system ? a)nail/wood system b) Bunsen burner, flask, balloon system

49 Work is done by the man causing frictional forces between the nail and the wood fiber. Work increases the internal energy of the wood and nail. Work done on a system: Work to Internal Energy

50 Work done by a system: Internal Energy to Work The balloon expands doing work on its surroundings The expanding balloon pushes the air away

51 Work done on or by a gas Volume must change or no work is done. On a gas- Volume decreases (work must be done to force molecules into a smaller area) By a gas- Volume increases (the pressure of the gas causes the volume to increase)

52 Section 5 Notes 4 Common Thermal Processes Isobaric Process Isochoric process (isovolumetric) Isothermal process Adiabatic process Each will have their own assumptions

53 4 Thermal Processes Isobaric Process – occurs at constant pressure ΔP = 0

54 4 Thermal Processes Isochoric process (Isovolumetric) – one that occurs at constant volume. ΔV = 0 and therefore W = 0

55 Thermal Processes Isothermal process – one that occurs at constant temperature T (temperature) directly relates to U (internal energy) ΔU = 0

56 Thermal Processes Adiabatic process – on that occurs with no transfer of heat ΔQ = 0

57 Example 8 How much heat has entered or left the system when 500J of work has been done on the system in an isothermal process?

58 Example 8 How much heat has entered or left the system when 500J of work has been done on the system in an isothermal process?

59 Example 9 How much work is done on or by the system when internal energy increases by 55J in n adiabatic process?

60 Example 9 How much work is done on or by the system when internal energy increases by 55J in n adiabatic process?

61 Section 6: Three Laws of Thermodynamics

62 First Law of Thermodynamics Energy Conservation: Conservation of energy applied to thermal systems. Energy can neither be created nor destroyed. It can only change forms When heat is added to a system, it transforms to an equal amount of some other form of energy. Equation: ΔU = Q + W (work is done on a system)

63 Second Law of Thermodynamics (Second Law) Law of Entropy –Heat goes from hot to cold. –No cyclic process is 100% efficient it can’t convert heat entirely into work Some energy will always be transferred out to surroundings as heat. –Energy systems have a tendency to increase their entropy or disorder. Entropy- Measure of randomness or disorder in a system

64 Third Law of Thermodynamics As a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value. A theoretical impossibility –If it occurred everything would stop and there would be no more entropy

65 Section 7: Transformation of energy in a heat engine

66 The Heat Engine –a device that used a difference in temperature of two substances to do mechanical work –It transferring energy from a high-temperature substance (the boiler) to a lower temperature substance –For each complete cycle: W net = Q h - Q c What the variables stand for here: Q h = Heat from high temperature substance Q c = Heat to low temperature substance W or work equals the difference of Q h and Q c

67 The Heat Engine How it works: main points There will be an area of high temperature (boiler) and an area of low temperature Heat wants to go from a high temperature to a low temperature. Work is done by capturing energy in the transfer and using it to do work The work done by the engine equals the difference in heat transferred from the hot to cold substance.

68 The Heat Engine –For each complete cycle: Work = Energy transferred as heat from the high temperature substance to the colder temperature substance What the variables stand for here: Q h = Heat from high temperature substance Q c = Heat to low temperature substance W or work equals the difference of Q h and Q c

69 Example 10 A heat engine is working at 50% efficiency. How much work is done between a 670J and 200J reservoir?

70 Example 10 A heat engine is working at 50% efficiency. How much work is done between a 670J and 200J reservoir?


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