In 1845, Michael Faraday discovered that the plane of polarization of linearly polarized light rotates when light rays move along the direction of the magnetic field in the presence of a transparent dielectric, an effect now known as Faraday rotation. [38] This was the first evidence that light is related to electromagnetism. In 1846, he hypothesized that light could be a form of disturbance propagating along magnetic field lines. [38] Faraday proposed in 1847 that light was a high-frequency electromagnetic oscillation that could propagate even in the absence of a medium such as ether. Fresnel later independently developed his own wave theory of light and presented it to the French Academy of Sciences in 1817.[39] Siméon Denis Poisson completed Fresnel`s mathematical work to make a convincing case for wave theory and overturn Newton`s corpuscular theory. [doubtful – discuss] In 1821, Fresnel was able to show with mathematical methods that polarization can only be explained by the wave theory of light if the light is completely transverse and without any longitudinal oscillation. [ref. needed] Pierre Gassendi (1592-1655), an atomist, proposed a theory of particles of light, which was published posthumously in the 1660s. Isaac Newton studied Gassendi`s work at a young age, preferring his view of Descartes` theory to the plenum. He stated in his 1675 light hypothesis that light consists of particles (particles of matter) emitted by a source in all directions.
One of Newton`s arguments against the wave nature of light was that waves were known to bend around obstacles, while light only moved in a straight line. However, he explained the phenomenon of light diffraction (observed by Francesco Grimaldi) by allowing a particle of light to produce a wave localized in the ether. If the concept of light is to include highly energetic photons (gamma rays), additional generation mechanisms include: Various physicists throughout history have tried to measure the speed of light. Galileo tried to measure the speed of light in the seventeenth century. A first experiment to measure the speed of light was conducted in 1676 by Ole Rømer, a Danish physicist. With a telescope, Rømer observed the motions of Jupiter and one of its moons, Io. He noticed discrepancies in the apparent period of Io`s orbit and calculated that light takes about 22 minutes to pass through the diameter of Earth`s orbit. [15] However, its size was not known at the time. If Rømer had known the diameter of the Earth`s orbit, he would have calculated a velocity of 227,000,000 m/s.
Some substances produce light when illuminated by higher energy radiation, a process known as fluorescence. Some substances emit light slowly after excitation by higher energy radiation. This is called phosphorescence. Phosphorescent materials can also be excited by bombarding them with subatomic particles. Cathodoluminescence is an example. This mechanism is used in CRT televisions and computer monitors. The main source of natural light on Earth is the sun. Historically, another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps. With the development of electric lighting and energy systems, electric lighting has effectively replaced fire lighting. Plant growth is also affected by the color spectrum of light, a process known as photomorphogenesis. Léon Foucault conducted an experiment in 1862 in which rotating mirrors obtained a value of 298,000,000 m/s.[16] Albert A. Michelson conducted experiments on the speed of light from 1877 until his death in 1931.
He refined Foucault`s methods in 1926 with improved rotating mirrors to measure the time it took to make a round trip from Mount Wilson to Mount San Antonio in California. Exact measurements showed a velocity of 299,796,000 m/s.[17] Another more accurate measurement of the speed of light was made in Europe in 1849 by Hippolyte Fizeau. [16] Fizeau directed a beam of light at a mirror several miles away. A rotating gear was placed in the path of the light beam as it moved from the source to the mirror and then returned to its origin. Fizeau found that at a certain rate of rotation, the beam passed through a gap in the wheel at the exit and the next space on the way home. Since Fizeau knew the distance to the rear-view mirror, the number of teeth on the wheel and the speed of rotation, he was able to calculate the speed of light at 313,000,000 m/s. Light does not penetrate anything. It can travel through the air here on Earth, but it does not depend on air to travel. It can also move in a vacuum. You read over the ether, so you know it doesn`t exist.
The first and most famous nail in the coffin was the Michelson-Morley experiment, which proved that the speed of light does not change depending on how we move in the (supposed) ether. The speed of propagation of electromagnetic waves in free space, an idealized standard reference state (such as absolute zero for temperature), is usually denoted c0:[1] Around 300 BC, Euclid Optica wrote in which he studied the properties of light.
