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For example, for visible light, the refractive index of glass is typically around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200 000 km/s (124 000 mi/s); the refractive index of air for visible light is about 1.0003, so the speed of light in air is about 90 km/s (56 mi/s) slower than c.
The particle usually comes from the radioactive decay of an atom of a radioisotope, an isotope of an element which is radioactive. The electron then returns to its ground energy level by emitting the extra energy as a photon of light. A chemical that releases light of a particular color when struck by ionizing radiation is called a phosphor ...
Passing white light through a prism splits it up into the several colours of light observed in the visible spectrum between 400 nm and 780 nm. If radiation having a frequency in the visible region of the EM spectrum reflects off an object, say, a bowl of fruit, and then strikes the eyes, this results in visual perception of the scene.
The speed of light in vacuum is defined to be exactly 299 792 458 m/s (approximately 186,282 miles per second). The fixed value of the speed of light in SI units results from the fact that the metre is now defined in terms of the speed of light. All forms of electromagnetic radiation move at exactly this same speed in vacuum.
The overall process of using a radioactive material to excite a phosphor and ultimately generate light is called radioluminescence. As tritium illumination requires no electrical energy, it has found wide use in applications such as emergency exit signs , illumination of wristwatches, and portable yet very reliable sources of low intensity ...
In electromagnetic radiation (such as microwaves from an antenna, shown here) the term radiation applies only to the parts of the electromagnetic field that radiate into infinite space and decrease in intensity by an inverse-square law of power, such that the total energy that crosses through an imaginary sphere surrounding the source is the ...
Air is tenuous enough that in the Earth's atmosphere radio waves travel at very nearly the speed of light. The wavelength λ {\displaystyle \lambda } is the distance from one peak (crest) of the wave's electric field to the next, and is inversely proportional to the frequency f {\displaystyle f} of the wave.
Radiation level in a range of situations, from normal activities up to the Chernobyl reactor accident. Each step up the scale indicates a tenfold increase in radiation level. Various doses of radiation in sieverts, ranging from trivial to lethal. Visual comparison of radiological exposure from daily life activities.