Thermal Physics, BRANCH OF PHYSICS, NEEDED BY IGCSE STUDENTS

BRANCH OF PHYSICS, NEEDED BY IGCSE STUDENTS

1. THERMAL PHYSICS IGCSE – PHYSICS

2. Thermal Effects Particles in Solids, Liquids, and Gases Temperature and Thermometers Expansion of Solids and Liquids Heating Gases Thermal Conduction Convection Thermal Radiation Liquids and Vapours Specific Heat Capacity Latent Heat

3. Moving Particles Solid Has fixed shape and volume. Its particles are held closely together by strong forces of attraction (bonds). They vibrate backwards and forwards but cannot change position

4. Moving Particles Liquid Has fixed volume but can flow to fill any shape. The particles are close together and attract each other. But they vibrate so vigorously that the attractions cannot hold them in fixed positions, and they can move past each other

5. Moving Particles Gas Has no fixed shape or volume and quickly fills any space available. Its particles are well spaced out, and virtually free of any attractions. They move about at high speed, colliding with each other and the walls of their container.

6. Moving Particles What are the particles? Elements is made from about 100 simple substances Atom is the smallest possible amount of an element Molecules is groups of atoms

7. Moving Particles Energy of particles The particles in solids, liquids, and gases have: kinetic energy because they are moving (energy because of motion Potential energy because their motion keeps them separated and opposes the bonds trying to pull them together. Gas have the most potential energy because they are furthest apart. Internal energy = kinetic energy + potential energy The hotter a material is, the faster its particles move, and the more internal energy it has Heat Thermal energy = internal energy or heat

8. Moving Particles Energy of particles The particles in solids, liquids, and gases have: kinetic energy because they are moving (energy because of motion Potential energy because their motion keeps them separated and opposes the bonds trying to pull them together. Gas have the most potential energy because they are furthest apart. Internal energy = kinetic energy + potential energy The hotter a material is, the faster its particles move, and the more internal energy it has Heat Thermal energy = internal energy or heat

9. Moving Particles

10. Temperature A temperature scale is a range of numbers for measuring the level of hotness. Most of the times we use Celcius degree to measure the level of temperature.

11. Temperature Objects at the same temperature have the same average kinetic energy per particle. The higher the temperature, the greater the average kinetic energy per particle. Temperature is not the same as heat. For example, a spoonsful of boiling water has exactly the same temperature (100 C) as a saucepanful of boiling water, but you could get far less thermal energy (heat) from it.

12. Temperature Absolute Zero and the Kelvin scale Absolute Zero As the temperature falls, the particles in a material lose kinetic energy and move more and more slowly. At -273 C, they can go no slower They would have minimum energy possible, since the law of physics do not allow particles to have zero energy.

13. Temperature

14. Temperature Fixing a temperature scale Two standard temperatures must be chosen: Lower fixed points  ice point (0 C)  pure ice Upper fixed point  steam point (100 C)  boiling point

15. Temperature Liquid-in-glass thermometers Nearly all liquids expand slightly when heated. This property is used in liquid-in-glass thermometers, which are normally filled with alcohol or mercury. Sensitivity Some thermometers are more sensitive to temperature change than others. The narrower the tube, the higher the sensitivity of the thermometer.

16. Temperature Liquid-in-glass thermometers Range Responsiveness Some thermometers respond more quickly to a change in temperature than others. A thermometer with a larger bulb, or thicker glass round the bulb, is less responsive because it takes longer for the alcohol or mercury to reach the temperature of the surroundings.

17. Temperature Liquid-in-glass thermometers Linearity Although mercury and alcohol thermometers must agree at the fixed points, they do not exactly agree at the other temperatures. That is because the expansion of one liquid is not quite linear compared with the other. However, within the 0-100 C, the disagreement is very small.

18. Temperature

19. Thermal Expansion – Solid & Liquid … the effect that increases the volume of a matter (solid, gas, and liquid) due to the increase of thermal Happens when a matter is heated up Kinetic theory Example, A steel before it is heated up and after

20. Thermal Expansion – Solid & Liquid Example, A steel before it is heated up and after Steel is heated  particles speed up  their vibrations take up more space  expanded

21. Thermal Expansion

22. Thermal Expansion – Solid & Liquid Water and Ice – Exception. Why? When hot water cools, it contracts, but when water freezes it expands and turns into ice. In liquid, the particles are close together In ice, the molecules link up in a very open structures that actually takes up more space than in liquid

23. Thermal Expansion – Gas Gas does not necessarily expand when heated  its volume depends on the container it is in. 3 important factors when dealing with gas: Pressure Volume Temperature Depends on its circumstance, a change in pressure can cause a change in volume or temperature or both, etc.

24. Thermal Expansion – Gas How pressure changes with temperature (at constant volume)

25. Thermal Expansion – Gas How volume changes with temperature (at constant pressure) When pressure is kept constant, then its temperature and volume would be increased

26. Thermal Expansion – Gas Effect on volume of pressure (temperature is constant) – Boyle’s law Boyle’s law: The pressure of a fixed mass of gas is inversely proportional to its volume if its temperature is kept constant or  

27. Thermal Expansion – Gas The gas laws Charles’ law – pressure is constant (ideal gas law)  is constant But, since pressure is constant: or   Charles’ law: The volume of a fixed mass of gas is directly proportional to its absolute temperature if the pressure is kept constant

28. Thermal Expansion – Gas The gas laws 2) Pressure law – volume is constant Pressure law: The pressure of a fixed mass of gas is directly proportional to its absolute temperature if the volume is kept consant .  

29. Thermal Expansion – Gas The gas laws 3) Boyle’s law – temperature is constant  

30. Thermal Expansion – Gas The gas laws 4) Combining the law  

31. Thermal Expansion – Gas Worked example A b icycle pump contains 50cm 3 of air at 17 C and at 1 atm. Find the pressure when the air is compressed to 10cm 3 and its temperature rises to 27 C. Answer 5.2 atm

32. Thermal Expansion – Gas

33. Thermal Expansion – Gas

34. Heat Transfers Conduction Convection Radiation

35. Liquid & Vapors Evaporation Condensation

36. Specific Heat Capacity When alcohol is burnt, its energy would be transferred to the surrounding. We can calculate the amount of heat transferred by the alcohol to the surrounding, by using: is heat transferred (J) is mass (kg) is specific heat capacity (J/kg C or J/kg K) is temperature change (in C or in K)  

37. Specific Heat Capacity A water with the mass of 2 kg cools from 70 C to 20 C. If the specific heat capacity of the water is 4200 J/kg C. Calculate the total of energy lost by water! Answer (negative sign indicate that water is loses its heat or energy)  

38. Specific Heat Capacity Specific heat capacity of several things:

39. Specific Heat Capacity Thermal capacity (heat capacity): It is the amount of energy (J) needed to increase 1 C of compound or mixture. is thermal capacity (J/ C) is mass is specific heat capacity  

40. Specific Heat Capacity Thermal capacity (heat capacity): From the previous question With the mass of 2 kg water, it means that: Or it means that it is needed 8400 J of energy to increase 1 C of water  

41. Specific Heat Capacity When alcohol is burnt, its energy is transferred to water above it through heat. If it is assumed that all heat is absorbed fully by the water, we can calculate the amount of heat transferred from the burning alcohol.  

42. Specific Heat Capacity Example  

43. Specific Heat Capacity Example It means that the total energy is lost from ethanol is 16 400 J or simply -16 400 J  

44. Specific Heat Capacity

45. Specific Heat Capacity Linking the power and specific heat capacity: So, is power (Watt or J/s) is time (s)  

46. Specific Heat Capacity

47. Specific Heat Capacity

48. Latent Heat Water can be a solid (ice), a liquid, or a gas called water vapour (or steam). There are its three phases, or states. Latent heat of fusion: It is the energy needed to separate the particles so that they can form the liquid If the liquid goes back to solid, it means that the energy is released.

49. Latent Heat Latent heat of fusion: Ice has a specific latent heat of fusion of 330 000 J/kg. It means that in order to change each kilogram of ice, it needed 330 000 J. Latent heat of vaporization: It is energy needed to separate the particles so that they can form a gas, but some required to push back the atmosphere as the gas forms. Water has latent heat of vaporization of 2 300 000 J/kg.

50. Latent Heat Therefore: is specific latent heat of fusion or vaporization (J/kg)  

51. Latent Heat