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Understanding Temperature and Heat

Learn about the concept of temperature, different temperature scales, and methods of temperature measurement. Explore the relationship between temperature, heat, and internal energy. Discover specific heat capacities and their applications.

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Understanding Temperature and Heat

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  1. Temperature Temperature 1 Next Slide Concept of Temperature • To feel the Hotness or coldness of an object • Different temperature scales and definitions of lower fixed point and upper fixed point Explanation • Definition of the temperature of the body : a measure of the average kinetic energy of each particle in that body • Absolute zero (273 C or 0 K)

  2. Temperature Temperature 2 Next Slide Concept of Temperature • At absolute zero, the average kinetic energy of each particle is minimum. • Thermometers : graduated tool used for temperature measurement. 1. Liquid-in-glass thermometer (3 kinds) (a) Mercury-in-glass thermometer Photo (b) Alcohol-in-glass thermometer Photo (c) Clinical thermometer Photo

  3. Temperature Temperature 3 Next Slide Concept of Temperature 2. Rotary thermometer Diagram 3. Resistance thermometer 4. Thermistor thermometer 5. Thermocouple thermometer

  4. Temperature Heat and Internal Energy 1 Next Slide Concept of Internal Energy • Unit of energy : Joule (J) • All objects are composed of small particles and every particle has both kinetic energy and potential energy. • Definition of Internal Energy : the sum of the kinetic and potential energy of all particles in the body Diagram • Rise in temperature means increase in internal energy.

  5. Temperature Heat and Internal Energy 2 Next Slide Concept of Heat • Different methods to increase the temperature of the object : 1. The object is hammered violently Diagram 2. The object is put in contact with a hotter object Diagram 3. Energy released in chemical reactions

  6. Temperature Heat and Internal Energy 3 Next Slide Heating Process • If a hot object is in contact with a cold object, internal energy is transferred from the hot object to the cold object. It is called the heating process.

  7. Temperature Heat and Internal Energy 4 Next Slide Heating Capacity Specific Heat Capacity • Devices to measure the energy transferred to the heater Photo • Experimental set-up to find the relationship between the amount of energy supplied and the rise in temperature Diagram

  8. The energy supplied by heating process to increase the temperature of a body by 1 K (or C) • Energy needed (released) • = Heat Capacity  the temperature raised (lowered) in °C Temperature Heat and Internal Energy 5 Next Slide Heating Capacity • Heat Capacity :

  9. The energy supplied by heating process to increase the temperature of an object with a mass of 1 kg by 1 K (or C) • Energy needed (released) • = Mass  Specific Heat Capacity  the temperature raised (lowered) in °C Temperature Heat and Internal Energy 6 Next Slide Specific Heat Capacity • Specific Heat Capacity :

  10. Substance Specific heat capacity (J kg-1°C-1) Water 4200 Methylated spirit 2400 Ice 2100 Aluminium 900 Glass 670 Iron 460 Lead 130 Temperature Heat and Internal Energy 7 Next Slide Specific heat capacities of common materials

  11. Temperature Heat and Internal Energy 8 Next Slide Worked Examples • Example 1 Calculation • Example 2 Calculation • Applications Explanation

  12. END of Temperature

  13. Temperature Temperature 1 Next Slide • Temperature scale : we choose two temperatures called the fixed points. We define the scale of temperature according to these two fixed points. • Celsius scale : lower fixed point (ice point) and upper fixed point (steam point) • Lower fixed point : temperature of melting point under normal atmospheric pressure is taken as 0C • Upper fixed point : temperature of steam over boiling water at normal atmospheric pressure is taken as 100C

  14. 0C melting ice boiling water 100C lower fixed point upper fixed point Temperature Temperature 1 Next Slide • Two marks are made on the thermometer to indicate the positions of lower fixed point (0C) and upper fixed point (100C).

  15. 0C 10C 20C 30C 40C 50C 60C 70C 80C 90C 100C 0C 10C 20C 30C 40C 50C 60C 70C 80C 90C 100C 273K 283K 293K 303K 313K 323K 333K 343K 353K 363K 373K Back to Temperature Temperature 1 Click Back to • Celsius temperature scale: • Kelvin temperature scale : Kelvin temperature = Celsius temperature + 273 • e.g. 0C = 273 K, 100C = 373 K, 273C = 0 K

  16. Back to Temperature Temperature 2 Click Back to • Mercury-in-glass thermometer : • It is a narrow glass tube. One end of the tube is made into a bulb which contains mercury and the other end is sealed. • Normal temperature range measured : 10C - 100C • Maximum temperature range measured : 39C - 357C

  17. Back to Temperature Temperature 2 Click Back to • Alcohol-in-glass thermometer: • It is a narrow glass tube. One end of the tube is made into a bulb which contains alcohol while the other end is sealed. • Normal temperature range measured : 30C - 60C • Maximum temperature range measured : 115C - 78C

  18. Back to Temperature Temperature 2 Click Back to • Clinical thermometer is shown below : • It is a special mercury-in-glass thermometer with a narrow bend in the tube. The scale used contains only a few degrees above and below the normal body temperature of 37C. It is used to measure the body temperature.

  19. 40 20 60 80 0 Back to Temperature Temperature 3 Click Back to • Rotary thermometer: • When the bimetallic strip with the pointer is heated, it bends because the metal on one side expands more than the metal on the other side.

  20. particles vibrate and have K.E. P.E. depends on the relative position of the particles Back to Temperature Heat and Internal Energy 1 Click Back to • Structure of a solid:

  21. Back to Temperature Heat and Internal Energy 2 Click Back to • A solid is hammered as shown below : • The particles are then forced to vibrate more vigorously, hence they possess more K.E. Temperature, which is a measure of the average K.E. of the particles, rises.

  22. Back to Temperature Heat and Internal Energy 2 Click Back to • A solid is in contact with another solid with a higher temperature • The particles in the solid with a lower temperature are forced to vibrate more vigorously (temperature rises). On the other hand, the particles in the solid with a higher temperature vibrate less vigorously (temperature drops).

  23. Temperature Heat and Internal Energy 4 Next Slide • Kilowatt-hour meter:

  24. Back to Temperature Heat and Internal Energy 4 Click Back to • Joulemeter :

  25. thermometer Joulemeter or kilowatt-hour meter water to power supply immersion heater polystyrene cup stirrer Temperature Heat and Internal Energy 4 Next Slide • The following set-up is used to investigate the relation between the energy supplied and the rise in temperature.

  26. Energy transfer E (J) 0 50 100 150 200 250 300 Temperature T (C) 20 23 26 28.5 32 35 37 Temperature rise T (C) 0 3 6 8.5 12 15 17 Energy transfer E graph of E vs. T temperature rise T (C) 0 Temperature Heat and Internal Energy 4 Next Slide • Results obtained :

  27. Energy transfer E (J) 135 172 221 248 Mass of water m (kg) 0.15 0.20 0.25 0.30 Temperature Heat and Internal Energy 4 Next Slide • We obtain a straight line which passes through the origin. This means that for a constant mass, the energy transfer is directly proportional to the temperature rise, that is, E  T for constant m. • Then we investigate how the energy transfer is related to the mass of water. The time taken to heat different masses of water through the same temperature rise, say 10C. • Results obtained :

  28. Energy transfer E graph of E vs. m mass of water m (kg) 0 Temperature Heat and Internal Energy 4 Next Slide • Again, we obtain a straight line which passes through the origin. This means that for a given temperature change, the energy transfer is directly proportional to the mass of water, that is, E  m for constant T.

  29. Back to Temperature Heat and Internal Energy 4 Click Back to • The polystyrene cup is used to hold the water. It is a bad conductor and so the energy lost to the surroundings is reduced. Moreover, it takes up little energy. • The stirrer is used to stir the water to maintain a homogeneous temperature in the water. • The Joulemeter (or kilowatt-hour meter) can measure the energy supplied to the immersion heater. The unit of the heater is kWh (kilowatt-hour). 1 kWh = 3600000 J

  30. thermometer oil immersion heater polystyrene cup stirrer Temperature Heat and Internal Energy 8 Next Slide • 2.25 kg of oil is put into the following set-up. • Initial reading of Joulemeter : 42500 J • Final reading of Joulemeter : 82500 J • Initial temperature : 30C • Initial temperature : 70C

  31. Heat capacity of the oil = • Specific heat capacity of the oil = Back to Temperature Heat and Internal Energy 8 Click Back to • Energy supplied by the Joulemeter = (82500  42500) J = 40000 J • Rise in temperature = (70  30)C = 40C

  32. Temperature Heat and Internal Energy 8 Next Slide • 2 kg of hot water at 80C is mixed with 4 kg of cold water at 20C. Suppose no energy is lost to the surroundings, what is the final temperature of the water? (Specific heat capacity of water : 4200 J kg-1C -1.

  33. Energy lost by the 2 kg water : • Energy gained by the 4 kg water : Back to Temperature Heat and Internal Energy 8 Click Back to • Let T°C be the final temperature • By the principle of conservation of energy, the amount of energy lost by the hot body = the amount of energy gained by the cold body

  34. Back to Temperature Heat and Internal Energy 8 Click Back to • Since water has a relatively high specific heat capacity, it needs a large amount of energy to raise the temperature of water. • Coolant of the engine of motor cars • Regulate the temperature of living organisms • Regulate the temperature of the land near the sea

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