When the two waves are in phase, i. e. the path difference is equal to an integral number of wavelengths, the summed amplitude, and therefore the summed intensity is maximum, and when they are in anti-phase, i. e. the path difference is equal to half a wavelength, one and a half wavelengths, etc., then the two waves cancel and the summed intensity is zero.

When light makes multiple reflections between two or more parallel surfaces, the multiple beams of light generally interfere with one another, resulting in net transmission and reflection amplitudes that depend on the light's wavelength.

When light strikes a material, most of the light is absorbed while a smaller amount of a particular frequency or wavelength is reflected.

When a beam of light crosses the boundary between a vacuum and another medium, or between two different media, the wavelength of the light changes, but the frequency remains constant.

When sodium or its compounds are introduced into a flame, they turn it yellow, because the excited 3s electrons of sodium emit a photon when they fall from 3p to 3s ; the wavelength of this photon corresponds to the D line at 589. 3 nm.

When wavelengths of electromagnetic radiation are quoted, the wavelength in vacuum usually is intended unless the wavelength is specifically identified as the wavelength in some other medium.

When a plane wave of wavelength λ with normal incidence, ( perpendicular to the grating ) each slit in the grating acts as a quasi point-source from which light propagates in all directions ( although this is typically limited to a hemisphere ).

When the path difference between the light from adjacent slits is equal to half the wavelength, λ / 2, the waves will all be out of phase, and thus will cancel each other to create points of minimum intensity.

When groove spacing is less than half the wavelength of light, the only present order is the m = 0 order.

When the photons belonging to the signal at a different wavelength from the pump light meet the excited erbium atoms, the erbium atoms give up some of their energy to the signal and return to their lower-energy state.

When the spectrum is reckoned per frequency interval, the Sun's peak emission appears at a frequency of 3. 43 x 10 < sup > 14 </ sup > Hz ; this means that the peak emission per unit frequency is at 3. 43 x 10 < sup > 14 </ sup > Hz, which corresponds to a wavelength of 883 nm and is well into the infrared.

When circularly polarized light passes through an absorbing optically active medium, the speeds between right and left polarizations differ ( c < sub > L </ sub > c < sub > R </ sub >) as well as their wavelength (< sub > L </ sub >< sub > R </ sub >) and the extent to which they are absorbed (< sub > L </ sub >< sub > R </ sub >).

When coherent light from the laser strikes a pit the material glows, giving off incoherent light of a different wavelength.

When this ratio is less than about one-tenth, Rayleigh scattering occurs in which the scattering coefficient varies inversely as the fourth power of the wavelength.

When the de Broglie wavelength was inserted into the Bragg condition, the observed diffraction pattern was predicted, thereby experimentally confirming the de Broglie hypothesis for electrons.

When an electron in the system absorbs a photon of light of the right wavelength, it can be promoted to a higher energy level.

When comparing the frequency and wavelength dependent expressions of the Rayleigh – Jeans law it is important to remember that

When the diameter of a particle is below or near the wavelength of light ( around 500 nanometers ), the particle cannot be seen in a light microscope with the usual method of illumination.

When a beam of neutrons emanating from a reactor is slowed down and selected properly by their speed, their wavelength lies near one angstrom ( 0. 1 nanometer ), the typical separation between atoms in a solid material.

When the size of the scattering center ( or grain boundary ) is reduced below the size of the wavelength of the light being scattered, the scattering no longer occurs to any significant extent.

When light strikes an object, it usually has not just a single frequency ( or wavelength ) but many.

When η has zero energy, like the infinite wavelength wave, it doesn't change at all.

When the Universe was very young, it was likely infused with dark energy, but with less space and everything closer together, gravity had the upper hand, and it was slowly braking the expansion.

When an aircraft is flying straight and level ( cruise ) most of the lift opposes gravity.

When it was pointed out to Niven that the Ringworld was dynamically unstable, in that once the center of rotation drifted away from the central sun, gravity would pull the ring into contact with the star, he used this as a plot element in the sequel novel, The Ringworld Engineers.

When a body at these points is perturbed, it moves away from the point, but the factor opposite of that which is increased or decreased by the perturbation ( either gravity or angular momentum-induced speed ) will also increase or decrease, bending the object's path into a stable, kidney-bean-shaped orbit around the point ( as seen in the rotating frame of reference ).

When a body ( body 1 ) is acted on by the gravity of another body ( body 2 ), the field can vary significantly on body 1 between the side of the body facing body 2 and the side facing away from body 2.

When these densities are divided, references to the spring constant, gravity and cross-sectional area simply cancel, leaving

When a pendulum is displaced sideways from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position.

When fusion no longer generates enough pressure to counteract gravity, the star rapidly collapses to form a black hole.

He does not explicitly acknowledge any anticipation of his demonstration of electrostatic repulsion by the latter but, as he quotes a passage from the same page, could not have been unaware that, in a discussion of the nature of electrical attraction, Cabeo had written ( Philosophia Magnetica p. 192 ): " When we see that small bodies ( corpuscula ) are lifted ( sublevari et attolli ) above the amber and also fall back to the motionless amber, it cannot be said that such erratic behaviour ( talem matum-but if " matum " is taken as a misprint for " motum ", then the translation is simply " such motion ") is an attraction by the gravity of the attracting body.

When moving within a rotating reference frame such as in a centrifuge or environment where gravity is simulated with centrifugal force, the coriolis effect causes a sense of motion in the vestibular system that does not match the motion that is seen.

When the head is tilted or the body position is changed with respect to gravity the displacement of the stones causes the hair cells to bend.

When long-range forces ( typically gravity or the Coulomb force ) are taken into account, then the interaction between each pair of particles needs to be computed.

When a liquid is poured into an open human mouth, the swallowing process is completed by peristalsis which delivers the liquid to the stomach ; much of the activity is abetted by gravity.

When installed vertically, glass ( or plastic ) bears its own weight because only a small area ( the top edge of the glazing ) is subject to gravity.

When gravity is negligible and using a Cartesian coordinate system for spacetime, the divergence of the non-gravitational stress – energy will be zero.

When a low, near-circular orbit around a body with substantial gravity ( as is required for many scientific studies ) is needed, the total required velocity changes can be on the order of several kilometers per second.

When a body is affected by a non-uniform external gravitational field, one can sometimes define a center of gravity relative to that field that will act as a point where the gravitational force is applied.

When it is necessary to consider a gravitational torque, it is easier to represent gravity as a force acting at the center of mass, plus an orientation-dependent couple.

When the quantum properties of gravity are not disregarded, spacetime itself becomes a quantum object, and therefore the usual logic of conventional quantum field theory, which requires the existence of a well defined classical geometry, does not work anymore.

When an aircraft is in cruise for example, lift does oppose gravity, but occurs at an angle when climbing, descending or banking.

When a fluid element is displaced on an interface or internally to a region with a different density, gravity tries to restore the parcel toward equilibrium resulting in an oscillation about the equilibrium state or wave orbit.

When the head is tilted or the body position is changed with respect to gravity, the displacement of the stones causes the hair cells to bend.

When balls reach the top of the elevator, gravity takes the ball to the ball track.

When the bodies reach sizes of approximately one kilometer, then they can attract each other directly through their mutual gravity, enormously aiding further growth into moon-sized protoplanets.