A level Thermal Physics Edexcel

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  • Thermal Physics
    • Heat and Temperature
      • Temperature
        • Heating an object causes its temperature to rise
        • If  the average  Kinetic energy of the molecules of a substance increases, then it has a higher temperature
        • It is the internal energy that determines the temperature
      • Heat transfer
        • Heating will becomes distributed  throughout a substance, with the heat being passed from hotter areas to colder ones.
      • Absolute zero is the point when the molecules will no longer be moving at all.  (-273 C)
    • Specific heat capacity
      • Depends on three things
        • 1. The amount of heat energy transferred
        • 2. The mass of the object
        • 3. The Specific heat capacity of the material from which the object is made.
      • A material has a given property known as its Specific Heat Capacity, C.
        • This is the energy needed to raise the temperature of 1kg of a particular substance by 1K
      • }E= mc}temp
        • Jkg-1 K-1
    • Iternal energy
      • If we sum the kinetic and the potential energies of a substance, we have measured its internal energy.
      • The internal energy is randomly distributed across all the molecules according to the      Maxwell-Boltzmann Distribution.
    • The Maxwell-Boltzmann distribution
      • If we plot the kinetic energy against the number of molecules that have that energy, we get a curved graph called the Maxwell-Boltzmann distribution
      • The characteristic shape of the graph shows that:
        • There are no molecules with zero energy.
        • Only a few molecules have high energies.
        • There is no maximum value for the energy a molecule can have.
      • The graph is for one specific temperature. As the temp changes so the graph changes.
      • Molecular kinetic energy
        • 1/2m<c2>=3/2kT
          • Were k is the Boltzmann constant, 1.38x10-23 JK-1
          • T is temp and it must be in kelvin
    • Root-Mean-Square Speed
      • This has the symbol ?<c2>
      • This is the speed associated with the average kinetic energy,  1/2m<c2>
      • To find the R.M.S
        • First, find the Square of each value
        • Then the average of the square values is.
        • Finally, take the square root to get the R.M.S speed.
    • Boyle's law
      • A law stating that the pressure of a given mass of an ideal gas is inversely proportional to its volume at a constant temperature.
        • P  & 1/v
    • Charles's law
      • The density of an ideal gas at constant pressure varies inversely with the temperature.
        • V & T
    • The Pressure law
      • For a constant mass of gas at a constant volume, the pressure exerted by the gas is proportion to its absolute temp
        • P & T
    • Ideal gases
      • 1. the molecules have zero size.
      • 2.  The molecules are identical.
      • 3. The molecules collide with each other and the wall of there container without any loss of energy, in collisions which take zero time.
      • 4. The molecules exert no forces on each other, except during collisions.
      • 5. There are enough molecules so that statistic can be applied.
      • pV=NkT
        • pV=nRT
          • n is the number of moles of the gas; R is the Universal gas constant,     R= 8.31 Jkg-1 mol-1
            • pV=NkT
              • pV=nRT
                • n is the number of moles of the gas; R is the Universal gas constant,     R= 8.31 Jkg-1 mol-1

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    يقوم المكيف بالتبريد بصفة مستمرة من خلال تكرار عملية تحويل السائل إلى غاز داخل أنابيب التبريد في المكيف فتمتص حرارة من داخل الغرفة ليتبخر السائل المبرد ويتحول إلى غاز، ثم يتم ضغط الغاز باستخدام محرك خاص فتنطلق الحرارة التي امتصها ليتحول إلى سائل مرة أخرى وتتم مرحلة الضغط في الجزء الخارجي من نظام التكييف، تتكرر العملية باستمرار سحب الحرارة من داخل الغرفة إلى خارج الغرفة ولكي يؤدي المكيف هذه المهمة بكفاءة فإن له دورة تعمل من خلال عدة مراحل وهي على النحو التالي : يقوم المحرك ضاغط غاز بضغط غاز الفريون مما يرفع درجة حرارته لأن حسب المبدأ الأول للديناميك الحرارية عندما نقوم بضغط غاز بقوة هائلة فإن جزيئات هذا الاخير تقترب بعضها من بعض مماينتج عنه ارتفاع في الطاقة الداخلية ومنه ارتفاع في الارتجاج الحراري ، وبالتالي ارتفاع في الحرارة ويزداد ضغطه كما هو موضح في الشكل الجزء الأيسر باللون الأحمر.

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