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Light with the same radiant intensity at other wavelengths has a lower luminous intensity. The curve which represents the response of the human eye to light is a defined standard function y (λ) or V (λ) established by the International Commission on Illumination (CIE, for Commission Internationale de l'Éclairage ) and standardized in ...
If light pressure were the cause of the rotation, then the better the vacuum in the bulb, the less air resistance to movement, and the faster the vanes should spin. In 1901, with a better vacuum pump, Pyotr Lebedev showed that in fact, the radiometer only works when there is low-pressure gas in the bulb, and the vanes stay motionless in a hard ...
It is particularly important in the design of vacuum device components such as cathodes. If defined as being close to a surface, then the vacuum level is typically not a constant due to the equilibrium electric fields in vacuum. The value of the vacuum level depends on the surface chosen due to variations in work function. [3]
The construction industry makes use of measures such as the R-value (resistance) and the U-value (transmittance or conductance). Although related to the thermal conductivity of a material used in an insulation product or assembly, R- and U-values are measured per unit area, and depend on the specified thickness of the product or assembly. [note 2]
The energy E of an electromagnetic wave in vacuum is found by the expression E = hf, where h is the Planck constant and f is its frequency. Bodies at higher temperatures emit radiation at higher frequencies with an increasing energy per quantum.
Light whose wavelength is well outside the visible spectrum has a luminous energy of zero, regardless of the amount of radiant energy present. The SI unit of luminous energy is the lumen second, which is unofficially known as the "talbot" in honor of William Henry Fox Talbot. In other systems of units, luminous energy may be expressed in basic ...
The relative static permittivity, ε r, can be measured for static electric fields as follows: first the capacitance of a test capacitor, C 0, is measured with vacuum between its plates. Then, using the same capacitor and distance between its plates, the capacitance C with a dielectric between the plates is measured.
The electron multiplier consists of a number of electrodes called dynodes. Each dynode is held at a more positive potential, by ≈100 Volts, than the preceding one. A primary electron leaves the photocathode with the energy of the incoming photon, or about 3 eV for "blue" photons, minus the work function of the photocathode. A small group of ...