The First Law of Thermodynamics

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Physics Fluid Mechanics and Thermal Physics

	The first law of Thermodynamics:
	The first law of thermodynamics is a generalization of the conservation of energy that encompasses changes in internal energy. This is universally valid law and can be applied to many processes and provides a connection between the microscopic and macroscopic worlds. There are two ways in which energy can be transferred between a system and its surroundings. One is through the work done by the system and other is through heat. Both mechanisms result in a change in the internal energy of the system and therefore usually result in measurable changes in the macroscopic variables of the system, such as the pressure, temperature, and volume of a gas. If a system undergoes a change from initial state to final state so that an amount of energy Q is transferred to the system and an amount of work W is done by the system, then the change in internal energy is nothing but Q-W: When the system undergoes an infinitesimal change in state in which a small amount of energy dQ is transferred by heat and a small amount of work dW is done , the internal energy changes by an amount dE_int This is the first law of thermodynamics which is basically an energy conservation equation. Heat Capacity and Specific Heat: Heat capacity (C) for a particular sample of a substance is defined as the amount of energy needed to raise the temperature of that substance by 1^oC If an amount of heat energy Q produces a change in temperature of a substance by ΔT, then it can be written as: The specific heat c of a substance is the heat capacity per unit mass. Thus, if energy Q is transferred by heat to mass m of a substance changes the temperature of the sample by ΔT, then the specific heat of the substance is: