What are the characteristics of light?
Photovoltaic cells are a device that converts the light energy of the sun into electrical energy, that is, uses light to directly generate electricity. What is solar energy and photovoltaic cell?Therefore, in order to understand photovoltaic cells, one must first understand the characteristics of light.
What is light? Light is the earliest natural phenomenon recognized by mankind. Optics is also one of the earliest developed disciplines in physics. As far back as the Zhou Dynasty, Chinese working people used copper concave mirrors to make fire and mirrors made of copper-tin alloy to illuminate people. In 400 BC, the “Mojing” recorded the linear propagation of light, and the imaging of plane mirrors, convex mirrors and concave mirrors. In the Song Dynasty, Shen Kuo made a detailed description of the small hole imaging, convex mirror and concave mirror imaging, and the focal point of the concave mirror in “Mengxi Bi Tan”. Ancient Greece and Egypt also made important contributions to the study of optics. At the beginning of the 17th century, Dutch physicists Lipsey, Galileo and Kepler created telescopes for astronomical observations (which played a decisive role in mastering and studying the laws of planetary motion). In 1621, Snell discovered the law of refraction of light that changes the direction of light propagation when light travels to the interface of two media.
The above is human’s understanding and application of light’s linear propagation, reflection and refraction phenomena. On this basis, it is not difficult for humans to ask questions about what light is. Since then, human research on light has entered the era of research on the nature of light.
What are the characteristics of light? Humans do not recognize the characteristics of light at once, but gradually recognize them after a long period of research and practice.
In 1905, American scientist Einstein explained the phenomenon of the photoelectric effect, which was inspired by the quantum theory of German scientist Planck. He believes that since electromagnetic waves are discontinuous when radiating energy, they are part by part, and the energy of each electromagnetic wave is E=hv, where h is the Planck constant and v is the frequency of the electromagnetic wave. And light waves are electromagnetic waves, so Einstein boldly proposed that the propagation of light is also discontinuous, one piece at a time, each piece of light is called a photon, and the photon energy E=hv, and v is the frequency of the photon. The frequency of light, h is still Planck’s constant. This theory is called the photon theory. The photon theory successfully explained the photoelectric effect and strongly proved the particle nature of light.
All the phenomena of light tell us that the classical theories summarized from macroscopic phenomena are no longer applicable to microscopic particles. In the macro concept, the wave and the particle are completely opposite, while the light wave is not the wave in the macro concept, and the photon is not the physical particle in the macro concept. Therefore, the volatility and particle nature of light are not just opposites, they are unified. A large number of photons show the wave nature of light, and a small number of photons show the particle nature of light; light shows the wave nature of light in the process of propagation, and when light interacts with matter, it shows the particle nature of light. Visible light has both wave and particle properties. That is, light has wave-particle duality.
Light is not a continuous flow of energy, but radiates and propagates in a single, disconnected, one-by-one form (ie, one photon). Each photon is a carrier of energy. The greater the energy of the photon, that is, the higher the frequency, the more obvious its particle properties; the smaller the energy of the photon, that is, the lower the frequency, the more obvious its volatility. In fact, not only photons have wave-particle duality, but all microscopic particles have wave-particle duality. Therefore, modern physics believes that the laws of microscopic particles are no longer explained by classical physical theories, but by quantum mechanics established after Planck’s quantum theory.
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