Physics 2.4 - Thermal properties and temperature - 2.pptx

Thermal properties

1. CHAPTER 6: HEAT

2. The energy that is being transferred between two bodies as a result of temperature difference is called heat. Heat is a form of energy which causes the sensation of hotness/Coldness.

3. Measurement of Heat C.G.S unit: erg Calorie : 1 calorie is defined as the amount of heat required for raising the temperature of 1g of water through 1 degree Celsius from 14.5oC to 15.5oC. S.I. unit: joule (J) The units calorie and joule are related as: 1 cal = 4.186 J (or nearly 4.2 J) 1 J = 0.24 cal 1 J = 107 erg

4. Temperature Heat always flow from a body at higher temperature to the body at lower temperature. At molecular level, when temperature increases (means body is gaining heat), kinetic energy of molecule increases, thus internal energy of that body increases. Ice point: The temperature at which pure water and ice are in equilibrium in a mixture at 1 atmospheric pressure, represented by 0°C (32°F) Steam point: The temperature at which water vapor condenses at a pressure of one atmosphere, represented by 100°C (212°F)

5. Measurement of Temperature T(K) = 273 + t A degree on Celsius is 1 /100 th part of the interval between the ice point and the steam point . A degree on Fahrenheit scale is 1 /180 th part of the interval between the ice point and the steam point. 1 centigrade degree = 9 /5 Fahrenheit degree  

6. HEAT AS A FORM OF ENERGY The Sun Gives Out Heat Heat is a form of energy. The Sun is the primary source of heat energy. Solid  liquid  gas Gas  liquid  solid ABSORB HEAT RELEASE HEAT

7. Test

8. Other Sources Of Heat Energy   Apart from the sun, we can get heat energy from : Electricity Fossil fuel Radioactive metals The mantle of the Earth. Heat is produced in our daily life wherever there is friction. Friction occurs when two objects rub against each other.   The Uses Of Heat In Our Daily Life.   Heat is a useful form of energy. The uses of heat in our daily life include : Cooking Food drying Boiling water Drying clothes Providing warmth and etc.

9. The Differences Between Heat And Temperature   Heat Temperature Is a form of energy due to motion of molecules in a substance. Is a degree of hotness or coldness of a body. It determines the flow of heat. Is measured in the joule ( J ) Is a measured in the Kelvin ( K ) Is the total amount of kinetic energy of a particles Tells us how fast the particles are moving. Two bodies having the same internal energy may differ in their temperature. Two bodies at same temperature may differ in the quantities of heat energy they can transfer When two bodies are placed in contact, the heat gained by one body is equal to the heat lost by another body. When two bodies at different temperatures are placed in contact, the resultant temperature is always lying between their initial temperatures. Heat is measured by using the principle of Calorimetry. Temperature is measured by a thermometer.

10. Effect of heat on matter

11. Thermometry Types of thermometer: (a) Mercury thermometer (b) Alcohol thermometer

12. Thermal Expansion of Solids: Effect of Heat on Solids Thermal Expansion Formula Linear Expansion: Volume Expansion (Cubical expansion) Superficial Expansion (Areal expansion)

13. Four rods, each of same initial length but made of copper, glass, iron and aluminium are heated to the same rise in temperature. Which rod will expand more? Specific heat of Copper is  0.385J/ goC Specific heat of glass is  0.84J/ goC Specific heat of iron is  0.450J/ goC Specific heat of Aluminium is  0.902J/ goC

14. Relation between Three Coefficients of Expansion

15. Apparent Expansion of Liquid and Real expansion of liquid

16. Anomalous Expansion of Water

17. Thermal Equilibrium Heat flows from a body at a higher temperature to a body at lower temperature till their temperatures become equal. Two bodies are said to be in thermal equilibrium, if they are at the same temperature.

18. SPECIFIC HEAT CAPACITY

19. Thermal (heat) capacity What requires more energy to heat up by 1 o C?

20. Thermal (heat) capacity What requires more energy to heat up by 1 o C? 1 kg water

21. Thermal (heat) capacity What requires more energy to heat up by 1 o C? 1 kg water 1 kg aluminium

22. Thermal (heat) capacity What requires more energy to heat up by 1 o C? 1 kg water 1 kg aluminium 4200 joules of energy 900 joules of energy

23. Thermal (heat) capacity What requires more energy to heat up by 1 o C? 1 kg water 1 kg aluminium 4200 joules of energy 900 joules of energy Water must be supplied with nearly five times as much energy as aluminium for the same rise in temperature.

24. Thermal (heat) capacity What requires more energy to heat up by 1 o C? 1 kg water 1 kg aluminium 4200 joules of energy 900 joules of energy Water must be supplied with nearly five times as much energy as aluminium for the same rise in temperature. It’s all to do with the SPECIFIC HEAT CAPACITY of the material

25. SPECIFIC HEAT CAPACITY Amount of heat (Q) absorbed or given out by a body depends upon the following factors: Mass of the body (m ). The rise or fall in temperature of the body The nature of the material which the body is made of Now we can say that: 𝑄 ∝ 𝑚∆𝑇 or, 𝑄 = 𝑚𝑠∆𝑇 Where s is a constant which explain heat absorption in terms of nature of material. It is a physical quantity which is known as specific heat or specific heat capacity

26. Thermal (heat) capacity The specific heat capacity of a substance is the amount of energy needed to change the temperature of 1kg of the substance by 1 o C.

27. Thermal (heat) capacity The specific heat capacity of a substance is the amount of energy needed to change the temperature of 1kg of the substance by 1 o C. Substance SHC (J / kg o C ) Water 4181 Oxygen 918 Lead 128

28. Thermal (heat) capacity The specific heat capacity of a substance is the amount of energy needed to change the temperature of 1kg of the substance by 1 o C. Substance SHC (J / kg o C ) Water 4181 Oxygen 918 Lead 128 Water has a particularly high SHC, making it very useful for storing heat energy, and for transporting it, eg . in central heating

29. Thermal (heat) capacity The equation (just what you wanted!)

30. Thermal (heat) capacity The equation (just what you wanted!) Energy transferred = mass x specific heat capacity x temperature Energy transferred = m c Δ T Where: m is the mass in kg, c is the SHC in J/( kg o C ) Δ T is the temperature change in o C (or in K)

31. Thermal (heat) capacity The equation How much energy needs to be transferred to raise the temperature of 2kg of water from 20 o C to 30 o C?

32. Thermal (heat) capacity The equation How much energy needs to be transferred to raise the temperature of 2kg of water from 20 o C to 30 o C? Energy transferred = mass x SHC x temp. change = 2 x 4181 x (30 – 20) = 2 x 4181 x 10 = 83,620 J = 83.62 kJ

33. Thermal (heat) capacity So what’s this ‘thermal capacity’ bit?

34. Thermal (heat) capacity So what’s this ‘thermal capacity’ bit? Thermal capacity = mass x SHC

35. Thermal (heat) capacity So what’s this ‘thermal capacity’ bit? Thermal capacity = mass x SHC e g . If there is 3kg of water in a kettle: Thermal capacity = 3 x 4181 = 12,543 J/ o C

36. Thermal (heat) capacity So what’s this ‘thermal capacity’ bit? Thermal capacity = mass x SHC e g . If there is 3kg of water in a kettle: Thermal capacity = 3 x 4181 = 12,543 J/ o C This means that for every 1 o C rise in temperature of the water in the kettle, 12,543 J of energy need to be supplied.

37. Measuring specific heat capacity

38. Measuring specific heat capacity http://www.schoolphysics.co.uk/age16-19/Thermal%20physics/Heat%20energy/text/Specific_heat_capacity_measurement/index.html Energy = power x time Apparatus for determining the SHC of a solid, eg . Aluminium Apparatus for determining the SHC of a liquid, eg . Water

39. Measuring specific heat capacity http://www.schoolphysics.co.uk/age16-19/Thermal%20physics/Heat%20energy/text/Specific_heat_capacity_measurement/index.html Energy = power x time Apparatus for determining the SHC of a liquid, eg . Water Beaker contains 0.75 kg of water. Immersion heater (200W) switched on for 200 seconds Temperature of the water rises by 12.5 o C Calculate the SHC of water

40. Measuring specific heat capacity http://www.schoolphysics.co.uk/age16-19/Thermal%20physics/Heat%20energy/text/Specific_heat_capacity_measurement/index.html Energy = power x time Apparatus for determining the SHC of a liquid, eg . Water Beaker contains 0.75 kg of water. Immersion heater (200W) switched on for 200 seconds Temperature of the water rises by 12.5 o C Calculate the SHC of water Energy transferred = power x time = 200 x 200 = 40,000J = 0.75 x c x 12.5 c = 40 000 / (0.75 x 12.5) SHC of water = 4267 J( kg o C )

41. Measuring specific heat capacity http://www.schoolphysics.co.uk/age16-19/Thermal%20physics/Heat%20energy/text/Specific_heat_capacity_measurement/index.html Energy = power x time Apparatus for determining the SHC of a liquid, eg . Water Beaker contains 0.75 kg of water. Immersion heater (200W) switched on for 200 seconds Temperature of the water rises by 12.5 o C Calculate the SHC of water Actual value for the SHC of water is 4181 J / kg o C . The method described does not make any allowance for heat loss to the surroundings or the beaker.

42. Thermal (heat) capacity Using the high SHC of water: Central heating system, water carries thermal energy from the boiler to the radiators. M Boiler R adiator Pump

43. Thermal (heat) capacity Using the high SHC of water: Central heating system, water carries thermal energy from the boiler to the radiators. M Boiler R adiator Pump In car cooling systems, water carries unwanted heat energy from the engine to the radiator.

44. Latent Heat

45. Solid Liquid Gas { melting { Boiling (evaporating) } condensing } freezing Latent Heat

46. Solid Liquid Gas { melting { Boiling (evaporating) } condensing } freezing Latent Heat Water has three phases or states : Solid (ice) Liquid Gas ( steam )

47. Latent Heat Thermal energy

48. Latent Heat Thermal energy Time

49. Latent Heat Thermal energy Time At this point the ice continues to absorb energy , but it’s temperature does not change .

50. Latent Heat Thermal energy Time At this point the ice continues to absorb energy , but it’s temperature does not change . The energy absorbed at this point is called the latent heat of fusion - It is needed to separate the particles so they can form a liquid .

51. Latent Heat Thermal energy Time At this point the ice continues to absorb energy , but it’s temperature does not change . The energy absorbed at this point is called the latent heat of fusion - It is needed to separate the particles so they can form a liquid . The energy is released again when a liquid changes back to a solid.

52. Latent Heat The specific latent heat of fusion of ice is 330 000 J/kg

53. Latent Heat The specific latent heat of fusion of ice is 330 000 J/kg This means that 330 000 joules of energy are transferred to change each kilogram of ice into water at the same temperature (0 o C).

54. Latent Heat The specific latent heat of fusion of ice is 330 000 J/kg This means that 330 000 joules of energy are transferred to change each kilogram of ice into water at the same temperature (0 o C). Equation: Energy transferred = mass x specific latent heat E = mL

55. Latent Heat The specific latent heat of fusion of ice is 330 000 J/kg This means that 330 000 joules of energy are transferred to change each kilogram of ice into water at the same temperature (0 o C). Equation: Energy transferred = mass x specific latent heat E = mL e g . If 3.5 kg of ice is melted (at 0 o C) E = mL Energy transferred = 3.5 x 330 000 E = 1 155 000 J

56. Latent Heat Measuring the specific latent heat of fusion of ice.

57. Latent Heat Measuring the specific latent heat of fusion of ice.

58. Latent Heat Measuring the specific latent heat of fusion of ice. 100 W immersion heater switched on for 300 seconds. Mass of water collected = 0.10kg E = mL L = E / m E = 100 x 300 = 30 000 J L = 30 000 / 0.10 = 300 000 J/kg Power = energy / time So, energy = Power x time

59. Latent Heat Measuring the specific latent heat of fusion of ice. 100 W immersion heater switched on for 300 seconds. Mass of water collected = 0.10kg E = mL L = E / m E = 100 x 300 = 30 000 J L = 30 000 / 0.10 = 300 000 J/kg Power = energy / time So, energy = Power x time Only an approximate figure for L as no allowance made for heat loss to the surroundings.

60. Latent Heat of Fusion Measuring the specific latent heat of fusion of ice. 100 W immersion heater switched on for 300 seconds. Mass of water collected = 0.10kg E = mL L = E / m E = 100 x 300 = 30 000 J L = 30 000 / 0.10 = 300 000 J/kg Power = energy / time So, energy = Power x time Only an approximate figure for L as no allowance made for heat loss to the surroundings.

61. Latent Heat of Vaporization

62. Latent Heat of Vaporization Water boils at 100 o C, producing steam.

63. Latent Heat of Vaporization Water boils at 100 o C, producing steam. If the kettle is not switched off, more thermal energy is absorbed by the water, producing more steam at 100 o C.

64. Latent Heat of Vaporization Water boils at 100 o C, producing steam. If the kettle is not switched off, more thermal energy is absorbed by the water, producing more steam at 100 o C. The energy absorbed by the water is called the latent heat of vaporization

65. Latent Heat of Vaporization Water boils at 100 o C, producing steam. If the kettle is not switched off, more thermal energy is absorbed by the water, producing more steam at 100 o C. The energy absorbed by the water is called the latent heat of vaporization Most of the thermal energy is need to separate the particles so they can form a gas. Some energy is required to push back the atmosphere as the gas forms.

66. Latent Heat of Vaporization The specific latent heat of vaporization of water is 2 300 000 J/kg

67. Latent Heat of Vaporization The specific latent heat of vaporization of water is 2 300 000 J/kg This means that 2 300 000 joules of energy are transferred to change each kilogram of liquid water into steam at the same temperature (100 o C).

68. Latent Heat of Vaporization The specific latent heat of vaporization of water is 2 300 000 J/kg This means that 2 300 000 joules of energy are transferred to change each kilogram of liquid water into steam at the same temperature (100 o C). Same equation as for the specific latent heat of fusion: E = mL But this time ‘L’ is the specific latent heat of vaporization .

69. Measuring the specific latent heat of vaporization of water. Latent Heat of Vaporization

70. Measuring the specific latent heat of vaporization of water. Latent Heat of Vaporization http://spmphysics.onlinetuition.com.my/2013/07/measuring-specific-latent-heat-of_6.html

71. Measuring the specific latent heat of vaporization of water. Latent Heat of Vaporization http://spmphysics.onlinetuition.com.my/2013/07/measuring-specific-latent-heat-of_6.html Power = energy / time So, energy = Power x time 100 W immersion heater switched on for 500 seconds. Mass of water boiled away = 20.0g E = mL L = E / m E = 100 x 500 = 50 000 J L = 50 000 / 0.02 = 2 500 000 J/kg

72. Measuring the specific latent heat of vaporization of water. Latent Heat of Vaporization http://spmphysics.onlinetuition.com.my/2013/07/measuring-specific-latent-heat-of_6.html Power = energy / time So, energy = Power x time 100 W immersion heater switched on for 500 seconds. Mass of water boiled away = 20.0g E = mL L = E / m E = 100 x 500 = 50 000 J L = 50 000 / 0.02 = 2 500 000 J/kg Only an approximate figure for L as no allowance made for heat loss to the surroundings.