Edexcel A2 Physics Unit 5 : Chapter 1 : Thermal Physics Prepared By: Shakil Raiman

1.1: Kinetic Theory of Matter A theory explaining the properties of matter based on the idea that at temperatures above absolute zero, molecules within matter are in motion. It infers that the internal energy of an object is derived from the motions and positions of its molecules.

1.1.1: Kinetic Theory of Matter In this model, matter is assumed to be made up of tiny particles called atoms or group of atoms joined together called molecules. These particles are in continuous and random motion.

1.2: Temperature and Heat Energy Temperature is the average kinetic energy of the molecules of an object. If the average kinetic energy of the molecules of a substance increases, then it is at a higher temperature Thermal Energy or heat energy is the sum of the kinetic energies of the molecules of an object. Thermal Energy or Heat Energy is transferred from a higher temperature region to a lower temperature region.

1.3: Absolute zero and Absolute temperature: Absolute zero: The temperature at which the pressure of an ideal gas becomes zero. This is 0 K on Kelvin scale. Absolute Temperature: The Kelvin or thermodynamic temperature scale with zero at -273 C.

1.4: Heat Capacity & Specific Heat Capacity: Same amount of transferred heat energy may not make same temperature rise in two different objects. The rise in temperature depends on: The amount of heat energy transferred The mass of the object The specific heat capacity of the material from which the object is made

1.4.1: Heat Capacity: The amount of heat energy that is needed to raise the temperature of an object by 1 °C or 1 K is called heat capacity. If an object needs H J of heat energy to raise the temperature by C = H/ Unit: JK-1

1.4.2: Specific Heat Capacity: The amount of heat energy that is needed to raise the temperature of 1 Kg of a substance by 1 °C or 1 K is called specific heat capacity. If an object having mass m Kg needs H J of heat energy to raise the temperature by C = H/(m) Unit: JKg-1K-1

1.4.3: Sp. Heat Capacity of Water: Water has high specific heat capacity which is 4200 JKg-1K-1. it can store a large amount of energy when it is heated up it can give out a large amount of energy when it cools down it heats up or cools down slower than other substance

1.4.4: Use of High Sp. Heat Capacity: Water is used as a good coolant in car engines, air-conditioning system and power station. The specific heat capacity of water is much higher than that of soil. Therefore, the same amount of energy is absorbed from the sunlight during daytime, the sea is heated up much slower than the land. Similarly, the sea cools down much slower than the land at night. These are the reasons why the coastal areas tend to have a smaller temperature difference by day and at night while the inland areas have a larger temperature difference. The inland areas have a hotter summers and colder winters than coastal areas. The water in our body keeps us from cooling down or warming up too quickly. This helps to maintain our body temperature uniform if the temperature of the surroundings changes drastically.

1.4.5: Heat Capacity of Mixtures: When two bodies of different temperature are mixed together: Heat energy lost by hot object = heat energy gained by the cold object

1.4.6: Measuring Specific heat capacity: Check on board

1.4.7: Specific heat capacity Values: Check on board

1.5: Melting & Boiling: Melting: When a solid is heated, it melts to a liquid. This process is called melting. The reverse process is called freezing. Boiling: When a liquid is heated, it boils to a gas. This process is called boiling. The reverse process is called condensation.

1.6: Internal Energy: The total random distribution of kinetic and potential energy of a collection of molecules or particles of an object is called internal energy.

1.7: Maxwell-Boltzmann distribution: The velocities of molecules in a gas are distributed according to 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.

1.8: Molecular Kinetic Energy: The average kinetic energy of any molecule in a gaseous sample is proportional to the absolute temperature of the gas. This relationship can be expressed in symbols as: <c2> is the mean square velocity. Where k is the Boltzmann constant, 1.38×10-23 JK-1, Here temperature, T, must be in kelvin.

1.9: Boyle’s Law: For a constant mass of gas at a constant temperature, the pressure exerted by the gas is inversely proportional to the volume it occupies.

1.9: Charles’s Law: For a constant mass of gas at a constant pressure, the volume occupied by the gas is proportional to its absolute temperature. This law can be shown in symbol as:

1.9: Pressure Law: For a constant mass of gas at a constant volume, the pressure exerted by the gas is proportional to its absolute temperature. The pressure law can be shown in symbol as:

1.10: Properties of Ideal Gas An ideal gas would have the following properties The molecules have zero size. The molecules are identical The molecules collide with each other and the walls of their containers without any loss of energy. Collisions take zero time The molecules exert no forces on each other, except during collisions. There are enough molecules so that statistics can be applied.

1.11: Equation of States: An equation relating the pressure, volume and temperature of an ideal gas is called equation of states. pV=NkT Where N is the number of molecules of the gas and k is the Boltzmann constant. The temperature must be absolute temperature in kelvin. pV = nRT Where n is the number of moles of the gas; and R is the Universal gas constant, R=8.31 Jkg-1mol-1 R=kNA where Avogadro number NA = 6.023×1023

Thank You All Wish you all very good luck.