Osm Physics by Ashish

Maxwell's thermodynamic relations are four fundamental equations that establish relationships among temperature (\(T\)), pressure (\(P\)), volume (\(V\)), and entropy (\(S\)). These relations are obtained from the fundamental thermodynamic equations by applying the mathematical properties of exact differentials. According to the first law of thermodynamics, \[ dU=\delta Q-\delta W \] For a reversible process involving only pressure-volume work, \[ \delta Q_{\mathrm{rev}}=T\,dS \qquad\text{and}\qquad \delta W_{\mathrm{rev}}=P\,dV \] Therefore, \[ \boxed{dU=T\,dS-P\,dV} \] (1) Here, \(U\) is internal energy, \(T\) is absolute temperature, \(S\) is entropy, \(P\) is pressure, and \(V\) is volume. Let \(U\), \(S\), and \(V\) be differentiable functions of two independent variables \(x\) and \(y\). Their total differentials are \[ dU= \left(\frac{\partial U}{\partial x}\right)_y dx+ \left(\frac{\partial U}{\partial y}\right)_x dy \] \[ ...

Regenerative Cooling, Adiabatic Expansion and Adiabatic Demagnetisation Definition: The cooling produced by reducing the magnetic field acting on a thermally isolated paramagnetic substance is called cooling by adiabatic demagnetisation . Principle A suitable paramagnetic salt, such as gadolinium sulphate, is placed in a thermally insulated glass tube. The tube is connected to a helium chamber and a vacuum system. The cooling assembly is surrounded by liquid helium. Additional cryogenic shielding may be used to minimize heat transfer from the surroundings. The sample is placed between the poles of a strong electromagnet. A magnetic field is therefore applied to the paramagnetic salt. The temperature can be determined from the magnetic susceptibility ...

Regenerative Cooling, Adiabatic Expansion and Adiabatic Demagnetisation Definition: The cooling produced when a compressed gas expands under adiabatic conditions is called cooling by adiabatic expansion . Adiabatic Relation For a reversible adiabatic expansion of an ideal gas, \[ PV^\gamma=\text{constant} \] where \[ \gamma=\frac{C_P}{C_V} \] Using the ideal-gas equation, the temperature-pressure relation becomes \[ TP^{(1-\gamma)/\gamma}=\text{constant} \] Therefore, between two states, \[ \boxed{ \frac{T_2}{T_1} = \left( \frac{P_2}{P_1} \right)^{(\gamma-1)/\gamma} } \] Hence, ...

Regenerative Cooling, Adiabatic Expansion and Adiabatic Demagnetisation Definition: Regenerative cooling is a continuous cooling process in which the cold gas produced by expansion is used to precool the incoming high-pressure gas before it undergoes further expansion. Principle of Regenerative Cooling In regenerative cooling, a portion of the gas that has already undergone Joule–Thomson expansion is passed through a heat exchanger in thermal contact with the incoming high-pressure gas. The returning cold gas cools the incoming gas before it reaches the throttle valve. The precooled gas then undergoes another Joule–Thomson expansion and becomes still colder. The process is repeated continuously. With each cycle, the temperature of the incoming gas decreases furth...

When a real gas is allowed to flow adiabatically through a porous plug from a region of high pressure to a region of low pressure, its temperature may change. This phenomenon is known as the Joule–Thomson effect , and the process is called Joule–Thomson expansion or throttling . Porous Plug Experiment The apparatus used in the Joule–Thomson porous-plug experiment is shown schematically in Fig. Consider a gas flowing through a thermally insulated tube containing a porous plug P . Two weightless and frictionless pistons X and Y are fitted on the two sides of the plug. The entire system is thermally insulated; hence, no heat is exchanged with the surroundings. Initially, let the gas occupy chamber A , having ...

  A charged particle produces an electric field in the space surrounding it. When another charged particle is placed in this field, it experiences an electric force. Thus, the electric field provides a physical description of the influence of a charge on the space surrounding it. The electric field at a point is defined as the region of space around a charge or a system of charges in which another charged particle experiences an electric force. The concept of the electric field was developed by Michael Faraday . Electric field is a vector field , since it has both magnitude and direction. It is quantitatively described in terms of electric field intensity .   Intensity of Electric Field The electric field intensity at a point is defined as the force experienced by a unit positive test charge placed at that point: where is the force acting on the test charge . The test charge is assumed to be a very small positive point charge , so that its presence does not appreciably distu...