Mohr’s Circle for Strain Analysis

Sublimation is a laboratory technique for purifying compounds, particularly volatile solids. The impure solid is gently heated, often under reduced pressure, causing it to sublime directly into a gas. This gas then deposits as a pure solid on a cooled surface, known as a cold finger, leaving the non-volatile impurities behind in the original container.

The color temperature is a characteristic of visible light that measures its hue on a scale from warm (yellowish) to cool (bluish). It is defined as the temperature of an ideal black-body radiator that radiates light of a comparable hue to that of the light source. The unit of measurement is kelvin (K).

The Galilean cannon demonstrates velocity multiplication through sequential, one-dimensional elastic collisions. When a stack of balls with decreasing mass is dropped, the bottom ball rebounds and collides with the one above. In an idealized case where a large mass \(m_1\) rebounds at velocity \(v\) and hits a much smaller mass \(m_2\) moving down at \(v\), the smaller mass is propelled upwards at nearly \(3v\).

The thermal efficiency (\(\eta_{th}\)) of an ideal Otto cycle is a function of the compression ratio (\(r\)) and the specific heat ratio (\(\gamma\)) of the working fluid. The formula is \(\eta_{th} = 1 - \frac{1}{r^{\gamma-1}}\). This equation shows that efficiency increases with the compression ratio, providing a fundamental principle for engine design and performance optimization.

The minimum feature size that a projection photolithography system can print is limited by diffraction and is approximated by the Rayleigh criterion. The critical dimension (CD) is given by \(CD = k_1 \cdot \frac{\lambda}{NA}\), where \(\lambda\) is the wavelength of light, NA is the numerical aperture of the lens, and \(k_1\) is a process-related coefficient. Smaller features require shorter wavelengths or higher numerical apertures.

Thermite possesses a very high activation energy, making it stable at room temperature and difficult to ignite. Ignition requires reaching temperatures of approximately 1,300 °C (2,400 °F). This is typically achieved not with a direct flame but with an intermediate, high-temperature initiator like a burning magnesium ribbon or a specially designed pyrotechnic fuse, which provides the necessary localized energy to start the reaction.

Planck's relation is a fundamental equation in quantum mechanics that quantifies the energy of a single photon. The formula is \(E = h\nu\), where \(E\) is the energy of the photon, \(\nu\) (nu) is its frequency, and \(h\) is the Planck constant. This relation establishes the particle-like nature of light, showing that its energy is quantized in discrete packets, or quanta.

The brilliant, iridescent blue of the Morpho butterfly's wings is not produced by pigments but by structural coloration. The wings are covered in microscopic scales with nano-structures shaped like tiny Christmas trees. These structures selectively reflect blue light through thin-film interference and diffraction, while absorbing other wavelengths, creating an intense, angle-dependent color.

Oxygen Balance (OB%) is a measure of the degree to which an explosive can be oxidized. If an explosive molecule contains enough oxygen to convert all its carbon to carbon dioxide and all its hydrogen to water, it has an OB% of zero. A positive OB% means excess oxygen is present, while a negative OB% indicates an oxygen deficit, affecting energy output and byproducts.

The Q10 temperature coefficient is a rule of thumb for estimating the effect of temperature on the rate of deterioration. For many chemical and biological systems, the rate of reactions approximately doubles for every 10°C (18°F) increase in temperature. This principle is widely applied to predict changes in the shelf life of food and pharmaceuticals under varying thermal conditions.

Energy is not continuous but comes in discrete packets called quanta. The energy \(E\) of a single quantum of electromagnetic radiation (a photon) is directly proportional to its frequency \(\nu\). This relationship is defined by the Planck-Einstein relation, \(E = h\nu\), where \(h\) is the Planck constant. This concept fundamentally challenged classical physics.