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  2. Negative refraction - Wikipedia

    en.wikipedia.org/wiki/Negative_refraction

    Negative refraction. Negative refraction is the electromagnetic phenomenon where light rays become refracted at an interface that is opposite to their more commonly observed positive refractive properties. Negative refraction can be obtained by using a metamaterial which has been designed to achieve a negative value for (electric) permittivity ...

  3. 1 + 2 + 3 + 4 + ⋯ - Wikipedia

    en.wikipedia.org/wiki/1_%2B_2_%2B_3_%2B_4_%2B_%E...

    Analytic continuation around the pole at s = 1 leads to a region of negative values, including ζ(−1) = ⁠− + 1 / 12 ⁠. In zeta function regularization , the series ∑ n = 1n {\textstyle \sum _{n=1}^{\infty }n} is replaced by the series ∑ n = 1n − s . {\textstyle \sum _{n=1}^{\infty }n^{-s}.}

  4. Numerical aperture - Wikipedia

    en.wikipedia.org/wiki/Numerical_aperture

    The numerical aperture with respect to a point P depends on the half-angle, θ1, of the maximum cone of light that can enter or exit the lens and the ambient index of refraction. As a pencil of light goes through a flat plane of glass, its half-angle changes to θ2. Due to Snell's law, the numerical aperture remains the same: NA = n1 sin θ1 ...

  5. Method of image charges - Wikipedia

    en.wikipedia.org/wiki/Method_of_image_charges

    Method of image charges. The method of image charges (also known as the method of images and method of mirror charges) is a basic problem-solving tool in electrostatics. The name originates from the replacement of certain elements in the original layout with fictitious charges, which replicates the boundary conditions of the problem (see ...

  6. 1/2 + 1/4 + 1/8 + 1/16 + ⋯ - Wikipedia

    en.wikipedia.org/wiki/1/2_%2B_1/4_%2B_1/8_%2B_1/...

    1/2 + 1/4 + 1/8 + 1/16 + ⋯. First six summands drawn as portions of a square. The geometric series on the real line. In mathematics, the infinite series ⁠ 1 2 ⁠ + ⁠ 1 4 ⁠ + ⁠ 1 8 ⁠ + ⁠ 1 16 ⁠ + ··· is an elementary example of a geometric series that converges absolutely. The sum of the series is 1. In summation notation ...

  7. Photon counting - Wikipedia

    en.wikipedia.org/wiki/Photon_counting

    Photon counting is a technique in which individual photons are counted using a single-photon detector (SPD). A single-photon detector emits a pulse of signal for each detected photon. The counting efficiency is determined by the quantum efficiency and the system's electronic losses. Many photodetectors can be configured to detect individual ...

  8. Elementary charge - Wikipedia

    en.wikipedia.org/wiki/Elementary_charge

    T I {\displaystyle {\mathsf {TI}}} Value. 1.602 176 634 × 10−19 C. ‍. [1] The elementary charge, usually denoted by e, is a fundamental physical constant, defined as the electric charge carried by a single proton or, equivalently, the magnitude of the negative electric charge carried by a single electron, which has charge1 e. [2] [a]

  9. Four color theorem - Wikipedia

    en.wikipedia.org/wiki/Four_color_theorem

    In mathematics, the four color theorem, or the four color map theorem, states that no more than four colors are required to color the regions of any map so that no two adjacent regions have the same color. Adjacent means that two regions share a common boundary of non-zero length (i.e., not merely a corner where three or more regions meet). [1]