London Dispersion Force

A quantum mechanical phenomenon where a wavefunction can propagate through a potential energy barrier. Classically, a particle lacking sufficient energy to surmount a barrier would be reflected. However, due to the wave-like nature of particles, there is a non-zero probability that the particle can appear on the other side of the barrier, effectively 'tunneling' through it.

A non-Newtonian fluid is one whose viscosity changes under an applied shear stress. Unlike a Newtonian fluid where viscosity is constant, its flow properties are not described by a linear relationship between shear stress (\(\tau\)) and shear rate (\(\dot{\gamma}\)). This dependency can manifest as shear-thinning (viscosity decreases with stress) or shear-thickening (viscosity increases with stress).

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.

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.

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.

It is impossible to simultaneously know with perfect accuracy certain pairs of complementary physical properties of a particle. The most common example is the position \(x\) and momentum \(p\). The principle states that the product of their uncertainties, \(\Delta x\) and \(\Delta p\), must be greater than or equal to a specific value: \(\Delta x \Delta p \ge \frac{\hbar}{2}\).

A light-emitting diode is a semiconductor p-n junction. When a suitable forward voltage is applied, electrons from the n-side and holes from the p-side are injected into the depletion region. As they recombine, energy is released. In direct band gap semiconductors, this energy is efficiently emitted as photons of light, a process known as electroluminescence.

Electrochemical potential, \(\bar{\mu}_i\), quantifies the total energy of a charged species `i` in a system. It combines the chemical potential, \(\mu_i\), which accounts for concentration and intrinsic properties, with the electrostatic potential energy, \(z_i F \phi\). The formula is \(\bar{\mu}_i = \mu_i + z_i F \phi\), where \(z_i\) is the ion's charge, \(F\) is the Faraday constant, and \(phi\) is the local electric potential.

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.

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.

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 \(H_0 = pK_{BH^+} - \log\left(\frac{[BH^+]}{[B]}}\right)\).

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.