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Waves. A wave is an oscillation or periodic movement that can transport energy from one point in space to another. Common examples of waves are all around us. Shaking the end of a rope transfers energy from your hand to the other end of the rope, dropping a pebble into a pond causes waves to ripple outward along the water's surface, and the expansion of air that accompanies a lightning strike ...
In a diamond crystal structure, each carbon atom forms strong covalent bonds with four neighbouring carbon atoms, and they create a tightly-packed 3D lattice structure and as a result what we get is a highly ordered and dense arrangement of carbon atoms, with no free electrons roaming around or energy states in the band gap, which is the energy range between the valence band, where electrons ...
But in fact carbon does form four bonds in graphite (carbon almost always forms four bonds—a central principle of organic chemistry). The trick is that the four bonds are not always equivalent; in graphite the fourth bond is not formed by the \(\mathrm{sp}^{2}\) bonding orbitals but rather involves an unhybridized \(2\mathrm{p}\) atomic orbital.
- Overview
- Ray theories in the ancient world
Light is electromagnetic radiation that can be detected by the human eye. Electromagnetic radiation occurs over an extremely wide range of wavelengths, from gamma rays with wavelengths less than about 1 × 10−11 metres to radio waves measured in metres.
What is the speed of light?
The speed of light in a vacuum is a fundamental physical constant, and the currently accepted value is 299,792,458 metres per second, or about 186,282 miles per second.
What is a rainbow?
A rainbow is formed when sunlight is refracted by spherical water droplets in the atmosphere; two refractions and one reflection, combined with the chromatic dispersion of water, produce the primary arcs of colour.
Why is light important for life on Earth?
While there is clear evidence that simple optical instruments such as plane and curved mirrors and convex lenses were used by a number of early civilizations, ancient Greek philosophers are generally credited with the first formal speculations about the nature of light. The conceptual hurdle of distinguishing the human perception of visual effects from the physical nature of light hampered the development of theories of light. Contemplation of the mechanism of vision dominated these early studies. Pythagoras (c. 500 bce) proposed that sight is caused by visual rays emanating from the eye and striking objects, whereas Empedocles (c. 450 bce) seems to have developed a model of vision in which light was emitted both by objects and the eye. Epicurus (c. 300 bce) believed that light is emitted by sources other than the eye and that vision is produced when light reflects off objects and enters the eye. Euclid (c. 300 bce), in his Optics, presented a law of reflection and discussed the propagation of light rays in straight lines. Ptolemy (c. 100 ce) undertook one of the first quantitative studies of the refraction of light as it passes from one transparent medium to another, tabulating pairs of angles of incidence and transmission for combinations of several media.
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With the decline of the Greco-Roman realm, scientific progress shifted to the Islamic world. In particular, al-Maʾmūn, the seventh ʿAbbāsid caliph of Baghdad, founded the House of Wisdom (Bayt al-Hikma) in 830 ce to translate, study, and improve upon Hellenistic works of science and philosophy. Among the initial scholars were al-Khwārizmī and al-Kindī. Known as the “philosopher of the Arabs,” al-Kindī extended the concept of rectilinearly propagating light rays and discussed the mechanism of vision. By 1000, the Pythagorean model of light had been abandoned, and a ray model, containing the basic conceptual elements of what is now known as geometrical optics, had emerged. In particular, Ibn al-Haytham (Latinized as Alhazen), in Kitab al-manazir (c. 1038; “Optics”), correctly attributed vision to the passive reception of light rays reflected from objects rather than an active emanation of light rays from the eyes. He also studied the mathematical properties of the reflection of light from spherical and parabolic mirrors and drew detailed pictures of the optical components of the human eye. Ibn al-Haytham’s work was translated into Latin in the 13th century and was a motivating influence on the Franciscan friar and natural philosopher Roger Bacon. Bacon studied the propagation of light through simple lenses and is credited as one of the first to have described the use of lenses to correct vision.
But in fact carbon does form four bonds in graphite (carbon almost always forms four bonds—a central principle of organic chemistry). The trick is that the four bonds are not always equivalent; in graphite the fourth bond is not formed by the sp 2 bonding orbitals but rather involves an unhybridized 2p atomic orbital.
- Melanie M. Cooper, Michael W. Klymkowsky
- 2020
Using light as a probe, scientists found innovative ways to make inferences about the inner structure of the atom. In this unit, we will follow the gradual change from considering the atom as a single indivisible particle to a later understanding of the atom composed of its constituent subatomic parts, including the electron, the first subatomic particle to be discovered, the proton, and the ...
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Is light a wave or a particle? How is it created? And why can’t humans see the whole spectrum of light? All your questions answered.
