Date of completion - Mar. 9th, 2021
The study of light is known as optics. Optics includes the study of the behavior and properties of light – such as the behavior of visible, ultraviolet and infrared light – as well as the interaction of light with matter. Light travels at the speed of 299,792,458 meters per second, representing the fastest that anything can travel, and an absolute upper limit on motion.
Light helps us in more ways than people could imagine. Light from the sun warms the Earth, creates day and night, and initiates the life-sustaining process of photosynthesis. Light provides a window on the universe, from cosmological to atomic scales. The analysis of the frequencies of light emitted and absorbed by atoms is a principal that leads to the development of quantum mechanics, and so much more.
First, what is light made of? Photons are particles smaller than atoms. They make light. For example, when a lamp is turned on, and it lights the room, it is actually spreading photons. The more photons, the brighter the light. Each photon carries a certain amount of energy depending on its wavelength. The shorter the wavelength, the greater its energy. The distance between the top of one wave and the top of the next wave is called a wavelength.
The light’s color also depends on its wavelength. For example, the color violet has the wavelength of 400 nanometers (nm), which is 0.00004 centimeters. UV (ultraviolet) light is light with a wavelength higher than violet, that is 400-10 nm. X-rays or gamma rays are also in that range. Humans can’t feel them until they are burned by them. That happens when the energy goes into the body and kill the cells. Infrared light also has a wavelength of 400-10 nm and is oblivious to the human eye. When the light is infrared, the photon can heat up what it hits. A heat lamp uses infrared light to heat something up.
Another thing about light is frequency. It is the number of times the wave crests per second. Frequency and wavelength are proportional, so the longer the wavelength, the lower the frequency, and vice versa. That's why a certain frequency means a certain amount of energy.
So, is light a wave, or a particle? The answer is both. That can be explained by the wave-particle duality principle. The wave-particle duality principle states that matter and light exhibit the behavior of both waves and particles.
In the 1600s, Christiaan Huygens and Isaac Newton both proposed theories for light's behavior. Huygens proposed a wave theory of light while Newton's was a particle theory of light. For over a century, Newton's theory was dominant. Then, in the early 19th century, Thomas Young's double slit experiment resulted in obvious wave behavior and seemed to support the wave theory of light over Newton's particle theory. It was until after Albert Einstein published his paper explaining the photoelectric effect, which said that light traveled as bundles of energy called photons (although the word photon hadn’t been used until years later), that it was confirmed – with a lot of additional experiments – that light functions as both a particle and a wave, depending on how the experiment is conducted and when observations are made.
All in all, the topic of light is more complicated than it looks. Theories relating to light have changed a lot over time, and might continue to do so.
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