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Section 1 Notes: Temperature Scales and Conversions

Section 1 Notes: Temperature Scales and Conversions. 1. How does a thermometer determine temperature?. Thermodynamics (Unit 1 spring). Thermodynamics- Physics that deals with heat and its conversion into other forms of energy. Temperature Variables. T K = Temperature Kelvin

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Section 1 Notes: Temperature Scales and Conversions

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

  2. Thermodynamics (Unit 1 spring)

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

  4. Temperature Variables • TK= Temperature Kelvin • TC= Temperature Celsius • TF= Temperature Fahrenheit

  5. Absolute Zero= 0 Kelvin, a temperature where no motion would occur. There is no kinetic energy in the molecules. • 0 Kelvin= -273.15 ºCelsius

  6. Conversion Scale ( )

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

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

  9. Example 2 • A time and temperature sign on a bank indicates the outdoor temperature is -20.0 ºC. What is the corresponding temperature on the Fahrenheit scale?

  10. Example 2 • A time and temperature sign on a blank indicates the outdoor temperature is -20.0 ºC. What is the corresponding temperature on the Fahrenheit scale?

  11. The Kelvin Temperature Scale • Has scientific significance due to its absolute zero point. • Has equal divisions as the Celsius scale • Not written in degrees • 0º C is 273.15 K • Therefore the conversion is:

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

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

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

  15. 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

  16. Click on the diagram to be taken to the page

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

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

  19. 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)

  20. Heat is energy in transit • Heat lost by one object equals heat gained by another • Heat lost = Heat gained • -QA = QB

  21. Heat transfers from hot to cold • Holding a hot cup • Holing a cold glass (heat leaving your hand feels cold)

  22. Example 3 • 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

  23. Tcan = 15º C Tcan = 5º C Twater = 20º C Twater = 35º C • Direction: From high temperature to low temperature • Rate of transfer depends on temperature difference: The greater temperature difference the greater the energy transfer

  24. Example 4 Where would the greater energy transfer take place and which way would the energy transfer? • Ice = 0 ºC Juice = 20 ºC • 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

  25. Tcan = 11º C Twater = 11º C What happens when the temperature inside and out are equal?

  26. Tcan = 11º C Twater = 11º C • Heat is transferred until there is thermal equilibrium • Thermal Equilibrium- When temperatures are equal and there is an even exchange of heat

  27. Section 4 Notes: Heat Transfer • Types of Heat Transfer: • Conduction • Convection • Radiation

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

  29. Thermal conductors- rapidly transfer energy as heat • Thermal insulators- slowly transfer energy as heat

  30. Challenge • Put the following in order of most thermally conductive to least. Copper, Wood, Air, Water, Concrete 1 2 3 4 5

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

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

  33. 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.

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

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

  36. Section 5: Laws of Thermodynamics

  37. 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

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

  39. In a system: How can you measure the quantity of heat entering or leaving? Q = Δ U or Q = Uf – U0 • Q: The quantity of heat that enters or leaves a system • U0: Initial internal energy in system • Uf: 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

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

  41. 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

  42. 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)

  43. 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?

  44. 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? 1500 - 2200 1500 + 2200

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

  46. Work done on a system:Work to Internal Energy • 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.

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

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