![]() ![]() ![]() Stars are often modeled as black bodies in astronomy. Hotter bodies, emit radiation with its spectrum shifted into higher and higher frequencies, into the visible part of the spectrum and start glowing red or even white when they are heated even more. Our bodies, when at their normal temperature of about 310 K (37 ☌), radiate only in the infrared part of the spectrum. At room temperature, the peak in this radiation is mostly in the infrared (thermal) region. The spectrum of light produced by a hot object depends on its temperature. The energy that was absorbed by a black body, is re-emitted in a wide spectrum and is called black-body radiation.īlack bodies are so important in physics because they do not reflect radiation, they only emit it like all other bodies. To stay in thermal equilibrium, it must emit radiation at the same rate as it absorbs the radiation. Black Body TemperatureĪ black body is an idealized physical body that absorbs all the electromagnetic radiation (light, radio waves, gamma rays, etc.) that strikes it. Photon energy is measured in any unit of energy, for example in joules or electronvolts (eV), 1 eV being equal to 1.602176565×10⁻¹⁹ J. As c and h are both constant, photon energy is inverse proportional to its wavelength and directly proportional to its frequency. s is the Plank’s constant and c is the speed of light in a vacuum.The relationship between photon energy E and its wavelength λ or frequency f is determined by the following equations, which are used in this calculator: The intensity of radiation does not affect the photon’s energy. Photon energy depends only on its frequency or wavelength. The higher the photon’s frequency, the greater its energy, and the higher the photon’s energy, the larger its frequency. ![]() The amount of energy carried by a single photon is directly proportional to the photon’s frequency and inversely proportional to its wavelength. In a vacuum, v = c, where c is the speed of light in a vacuum, the expression above becomes: Note that in a dispersive media, for example, in optical glass, the speed depends on frequency and therefore the wavelength is not completely inversely proportional to the frequency. Where v is the phase velocity of the wave in a media. For such periodic waves, the frequency f has an inverse relationship to the wavelength λ: Definitions and Formulas Frequency and WavelengthĮlectromagnetic radiation is the flow of energy in the form of periodic oscillations of electric and magnetic fields that can propagate through a vacuum at the speed of light or through any medium that is transparent to them at a speed less than the speed of light. ![]()
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