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  2. Negative frequency - Wikipedia

    en.wikipedia.org/wiki/Negative_frequency

    Let ω > 0 be an angular frequency with units of radians/second. Then the function f(t) = −ωt + θ has slope −ω, which is called a negative frequency.But when the function is used as the argument of a cosine operator, the result is indistinguishable from cos(ωt − θ).

  3. Spectral density - Wikipedia

    en.wikipedia.org/wiki/Spectral_density

    To find the value of the energy spectral density ¯ at frequency , one could insert between the transmission line and the resistor a bandpass filter which passes only a narrow range of frequencies (, say) near the frequency of interest and then measure the total energy () dissipated across the resistor.

  4. Wavenumber - Wikipedia

    en.wikipedia.org/wiki/Wavenumber

    where ν is the frequency of the wave, λ is the wavelength, ω = 2πν is the angular frequency of the wave, and v p is the phase velocity of the wave. The dependence of the wavenumber on the frequency (or more commonly the frequency on the wavenumber) is known as a dispersion relation.

  5. Q factor - Wikipedia

    en.wikipedia.org/wiki/Q_factor

    The Q factor is a parameter that describes the resonance behavior of an underdamped harmonic oscillator (resonator). Sinusoidally driven resonators having higher Q factors resonate with greater amplitudes (at the resonant frequency) but have a smaller range of frequencies around that frequency for which they resonate; the range of frequencies for which the oscillator resonates is called the ...

  6. Zero-point energy - Wikipedia

    en.wikipedia.org/wiki/Zero-point_energy

    In 1900, Max Planck derived the average energy ε of a single energy radiator, e.g., a vibrating atomic unit, as a function of absolute temperature: [24] = / (), where h is the Planck constant, ν is the frequency, k is the Boltzmann constant, and T is the absolute temperature. The zero-point energy makes no contribution to Planck's original ...

  7. Redshift - Wikipedia

    en.wikipedia.org/wiki/Redshift

    In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and energy, is known as a blueshift, or negative redshift.

  8. Dispersion relation - Wikipedia

    en.wikipedia.org/wiki/Dispersion_relation

    As mentioned above, when the focus in a medium is on refraction rather than absorption—that is, on the real part of the refractive index—it is common to refer to the functional dependence of angular frequency on wavenumber as the dispersion relation. For particles, this translates to a knowledge of energy as a function of momentum.

  9. Negative energy - Wikipedia

    en.wikipedia.org/wiki/Negative_energy

    The negative-energy particle then crosses the event horizon into the black hole, with the law of conservation of energy requiring that an equal amount of positive energy should escape. In the Penrose process , a body divides in two, with one half gaining negative energy and falling in, while the other half gains an equal amount of positive ...