Why Does an Upright Stick Appear Broken in Water: The Physics Behind Refraction
The phenomenon where an upright stick appears to be broken when placed in water is a fascinating example of the behavior of light, known as refraction. This effect can be understood by examining the interaction between light photons and transparent media of varying optical densities.
The Intricacies of Photon Behavior and Optics
The term "look" in this context refers to the field of optics, which studies the behavior of photons (particles of light) as they interact with different transparent media. For a retired optical design engineer with over four decades of experience, understanding these interactions is crucial. When photons pass through transparent media of varying optical densities, their direction changes, a phenomenon known as refraction. Interestingly, the word used in my native language to describe this concept is more akin to "broken" than "bent." This nuance highlights the differences in how we perceive and describe physical phenomena across languages.
The Physics of Refraction and Feynman's Insights
The underlying physics of refraction is explained in a paper by physicist Richard Feynman, who taught at CalTech. His insights can be explored through his recorded video lectures on YouTube. Feynman emphasizes that refraction is fundamentally about time. Time acts as the metric in physics that measures the rate and duration of observed actions. When Feynman refers to "time," he is discussing the rate at which energetic transactions occur, particularly at the quantum scale.
When a photon interacts with the bound electromagnetic (EM) fields surrounding the atomic nuclei of atoms in a transparent medium, this interaction significantly affects the rate and duration it takes for the transaction to occur. These interactions cause two observable effects: the transit time of the photon is slowed down, about 75% of the speed of light (c) in water, and the direction of the incident ray is altered based on the refractive index of the medium relative to the kinetic energy of the photon. This alteration in direction is why the apparent position of the stick in water changes, making it appear to be broken.
The Prismatic Effect and Rainbow Colors
The separation of colors in a light ray, commonly observed as a rainbow when light strikes a reflective surface, is another fascinating aspect of refraction. This effect is caused by the different energies of light particles (photons). High-energy photons, such as blue, purple, and violet light, refract more than low-energy photons like green, yellow, orange, and red light. Consequently, when a so-called "white" light ray strikes a reflective surface, the higher-energy photons bend more sharply, resulting in a prismatic separation of colors. This visible breakdown of light colors is what we commonly observe as a rainbow.
In summary, the apparent breakage of an upright stick in water is a brilliant demonstration of the complexities of photon behavior and the principles of optics. Understanding the physics behind refraction, as explained by Feynman, provides a deeper appreciation for the intricate workings of light and its interactions with matter. This knowledge not only piques our curiosity but also enhances our ability to design and understand optical technologies, making it an essential topic for anyone interested in the wonders of science.
Keywords: optics, refraction, photon behavior