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Meissner Effect

1933

Walther Meissner
Robert Ochsenfeld

(generated image for illustration only)

Discovered in 1933 by Walther Meissner and Robert Ochsenfeld, the Meissner effect is the expulsion of a magnetic field from a superconductor during its transition to the superconducting state. When a material is cooled below its critical temperature (\(T_c\)) in the presence of a weak external magnetic field, it actively cancels all magnetic flux inside it, becoming a perfect diamagnet.

The Meissner effect is a defining characteristic of superconductivity, distinguishing it from a hypothetical perfect conductor. A perfect conductor, according to Lenz’s law, would trap any existing magnetic field inside it as it cools, because changing the flux would induce currents to oppose the change. In contrast, a superconductor actively expels the field. This expulsion is achieved by the generation of screening currents on the surface of the material. These currents create a magnetic field that perfectly cancels the external field within the bulk of the superconductor. The magnetic field penetrates only a small distance into the surface, known as the London penetration depth (\(\lambda\)). This discovery was crucial because it showed that superconductivity is a true thermodynamic phase transition, not just a case of infinite conductivity. It provided a key piece of the puzzle that any microscopic theory of superconductivity would have to explain. The effect is the basis for the dramatic levitation demonstrations where a magnet floats above a high-temperature superconductor cooled with liquid nitrogen. The expulsion of the magnet’s field by the superconductor creates a repulsive force strong enough to counteract gravity.

The Meissner effect breaks down when the applied magnetic field is too strong. For Type I superconductors, superconductivity is abruptly destroyed above a critical field \(H_c\). For Type II superconductors, the field begins to penetrate the material in the form of quantized flux vortices above a lower critical field \(H_{c1}\), while the material remains superconducting until a much higher upper critical field \(H_{c2}\).

Cryogenics, Electromagnetism, Magnetic Resonance Imaging (MRI), Materials Science, Quantum Error Correction, Super Capacitors

UNESCO Nomenclature: 2211

– Solid state physics

Type

Physical Property

Disruption

Foundational

Usage

Widespread Use

Precursors

discovery of superconductivity (1911)
Maxwell’s equations of electromagnetism
Lenz’s law
understanding of diamagnetism

Applications

maglev trains (magnetic levitation)
superconducting magnetic bearings
diagnostics of superconducting materials
demonstrations of quantum phenomena

Patents:

Potential Innovations Ideas

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Related to: Meissner effect, superconductivity, diamagnetism, magnetic field expulsion, London penetration depth, critical temperature, Type I superconductor, screening currents, magnetic levitation, phase transition.

Historical Context

London Dispersion Force

The London dispersion force (LDF) is the weakest type of Van der Waals force, arising from quantum mechanical fluctuations in the electron clouds of atoms and molecules. These fluctuations create temporary, instantaneous dipoles that induce corresponding dipoles in neighboring atoms, resulting in a net attractive force. The interaction potential energy \(V\) between two atoms at distance \(r\) is approximately \(V = -\frac{C_6}{r^6}\).

Colorimeter measuring light sources in a laboratory for colorimetry applications.

Planckian Locus

The Planckian locus is the path that the color of an incandescent black-body radiator follows in a chromaticity space as its temperature changes. It is typically plotted on the CIE 1931 xy chromaticity diagram, appearing as an arc from the reddish-orange region to the bluish-white region. It serves as the fundamental reference for defining color temperature.

Laboratory analysis of ultraviolet spectrum subdivisions for photometry applications.

Ultraviolet Spectrum Subdivisions (UVA, UVB, UVC)

The ultraviolet spectrum is commonly subdivided into UVA (400–315 nm), UVB (315–280 nm), and UVC (280–100 nm). UVA, or long-wave UV, is the least energetic and penetrates the skin deepest. UVB, or medium-wave UV, causes sunburn and is crucial for vitamin D synthesis. UVC, or short-wave UV, is the most energetic and germicidal but is completely absorbed by Earth's atmosphere.

Meissner Effect

Laboratory experiment demonstrating Hamaker Theory in physical chemistry of surfaces.

Hamaker Theory (physics)

A theory that extends the microscopic Van der Waals forces between individual atoms to the macroscopic scale, calculating the total interaction force between bulk objects (e.g., two spheres, a sphere and a plate). It assumes pairwise additivity, integrating the microscopic \(r^{-6}\) potential over the volumes of the interacting bodies. The result is quantified by the Hamaker constant, \(A\).

P-N junction in a solar cell demonstrating semiconductor physics.

The P-N Junction Photovoltaic Principle

A solar cell's core is a p-n junction, an interface between p-type and n-type semiconductor materials. This junction creates a built-in electric field in a depletion region. When photons with sufficient energy strike the semiconductor, they create electron-hole pairs. The electric field separates these charge carriers, driving electrons to the n-side and holes to the p-side, generating a voltage.

Researcher demonstrating the Weissenberg Effect with viscoelastic fluid in a laboratory.

The Weissenberg Effect (fluids)

The Weissenberg effect is a phenomenon in viscoelastic fluids where the fluid climbs up a rotating rod inserted into it. This is contrary to the behavior of Newtonian fluids, which are pushed outwards by centrifugal force, forming a vortex. The effect is caused by normal stress differences that develop in the fluid under shear.

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Laboratory scene demonstrating thermoelectricity applications with Peltier cooler and generator.

Onsager Reciprocal Relations

A key theorem in non-equilibrium thermodynamics, these relations express the equality of certain cross-coefficients between coupled flows of energy and matter. They state that in the absence of a magnetic field, the matrix of transport coefficients is symmetric: \(L_{\alpha\beta} = L_{\beta\alpha}\). This links seemingly unrelated transport phenomena, such as the Seebeck and Peltier effects in thermoelectricity.

Laboratory technician measuring Correlated Color Temperature of LED light sources with a spectrometer.

Correlated Color Temperature (CCT)

Correlated Color Temperature (CCT) is a metric for light sources that do not radiate as ideal black bodies, such as LEDs or fluorescent lamps. It is the temperature of the Planckian radiator whose color is perceived as most similar to the light source. This 'closeness' is determined by finding the point on the Planckian locus nearest to the source's chromaticity coordinates.

Perfect Reflecting Diffuser in a laboratory for colorimetry and spectrophotometry calibration.

Perfect Reflecting Diffuser (PRD)

The Perfect Reflecting Diffuser, also known as a perfect white, is a theoretical, idealized surface used as a reference standard in colorimetry and spectrophotometry. It is defined as a surface that reflects 100% of all incident light at every wavelength in the visible spectrum and reflects this light perfectly diffusely (lambertian reflectance), meaning its brightness is uniform from any viewing angle.

Chemist measuring superacid solutions in an organic chemistry laboratory.

Superacids and the Hammett Acidity Function

A superacid is an acid with an acidity greater than that of 100% pure sulfuric acid. The conventional pH scale is inadequate for these media. Instead, their acidity is measured using the Hammett acidity function, \(H_0\). This function is based on the protonation of weak indicator bases and is defined as \(H_0 = pK_{BH^+} - \log\left(\frac{[BH^+]}{[B]}}\right)\).

Industrial facility for hydrogen peroxide production using the anthraquinone process.

The Anthraquinone Process for H₂O₂ Production

The anthraquinone process, developed in the 1930s, is the dominant industrial method for producing hydrogen peroxide. It involves the hydrogenation of an anthraquinone derivative to an anthrahydroquinone, followed by its oxidation with air to regenerate the original anthraquinone and produce hydrogen peroxide. The H₂O₂ is then extracted with water and concentrated, creating a continuous, efficient cycle.

Chemist balancing redox equations in a laboratory, showcasing oxidation state in inorganic chemistry.

The Oxidation State Concept (oxidation number)

The oxidation state, or oxidation number, is a hypothetical charge that an atom would have if all its bonds to different atoms were 100% ionic. It provides a way to track electron transfer in redox reactions. An increase in oxidation state signifies oxidation, while a decrease signifies reduction. This formalism simplifies the analysis of complex chemical reactions.

Thermate Composition

Thermate is an incendiary composition that enhances standard thermite. It is typically a mixture of thermite, barium nitrate (\(Ba(NO_3)_2\)), and sulfur. The barium nitrate acts as an oxidizer, increasing the thermal output and making the reaction less dependent on atmospheric oxygen. Sulfur is added primarily to lower the ignition temperature, making the mixture easier and more reliably ignited.

Plasticity Theory

Plasticity is the theory describing the deformation of a solid material undergoing non-reversible changes of shape in response to applied forces. Unlike elasticity, where deformation is recovered upon unloading, plastic deformation is permanent. The theory involves a yield criterion to define the onset of plasticity, a flow rule to describe the evolution of plastic strain, and a hardening rule.

(if date is unknown or not relevant, e.g. "fluid mechanics", a rounded estimation of its notable emergence is provided)