Kelvin (Thomson) Relations

The Clausius-Clapeyron relation describes the relationship between pressure and temperature for a substance at a phase transition, such as liquid and vapor. For water vapor, it shows that saturation vapor pressure increases exponentially with temperature. The approximate form is \(\frac{dp}{dT} = \frac{L}{T(V_v - V_l)} \approx \frac{L p}{R_v T^2}\), where L is latent heat.

Eddy currents are loops of electrical current induced within bulk conductors by a changing magnetic field, in accordance with Faraday's law. They flow in closed loops in planes perpendicular to the magnetic field. Following Lenz's law, these currents create their own magnetic field that opposes the change in the external flux, causing a repulsive or drag force and resistive heating.

Lead-Acid battery type is the first rechargeable battery, invented by Gaston Planté in 1859. It operates using a lead (Pb) anode and a lead dioxide (PbO₂) cathode immersed in a sulfuric acid (H₂SO₄) electrolyte. During discharge, both electrodes convert to lead sulfate (PbSO₄), a process that is reversed during charging, allowing for energy storage and reuse.

This is the differential form of Faraday's law of induction, one of Maxwell's four equations. It states that a time-varying magnetic field (\(\mathbf{B}\)) always accompanies a spatially varying, non-conservative electric field (\(\mathbf{E}\)). The relationship is expressed as \(\nabla \times \mathbf{E} = -\frac{\partial \mathbf{B}}{\partial t}\). This equation governs how changing magnetic fields create electric fields at a specific point in space.

Maxwell's equations are a set of four coupled partial differential equations that form the foundation of classical electromagnetism. They describe how electric and magnetic fields are generated and altered by each other and by charges and currents. They are Gauss's law, Gauss's law for magnetism, Faraday's law of induction, and the Ampère-Maxwell law.

The Joule-Thomson (or Joule-Kelvin) effect describes the temperature change of a real gas when it is forced through a valve or porous plug while kept insulated (an isenthalpic process). At a given pressure, a gas has an inversion temperature. If expanded below this temperature, it cools; if expanded above it, it heats up. This cooling effect is a cornerstone of modern refrigeration and liquefaction.

The first commercially successful rechargeable battery. It uses a lead (Pb) anode, a lead dioxide (PbO₂) cathode, and a sulfuric acid (H₂SO₄) electrolyte. During discharge, both electrodes are converted into lead sulfate (PbSO₄), and the sulfuric acid is consumed. This process is chemically reversible by applying an external current, making it a practical and robust energy storage system.

One of the four Maxwell's equations, Gauss's law for magnetism states that the net magnetic flux out of any closed surface is zero. This is expressed mathematically as \(\oint_S \vec{B} \cdot d\vec{A} = 0\). This law is a statement of the experimental observation that magnetic monopoles (isolated north or south poles) have never been detected. Magnetic field lines always form closed loops.

Electromagnetic waves are disturbances of the electromagnetic field that propagate through space, carrying energy. They are created by accelerating electric charges and consist of synchronized, perpendicular oscillations of electric and magnetic fields. In a vacuum, they travel at the speed of light, \(c\). The electromagnetic spectrum encompasses radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.