In sunlight, infrared light is produced by charges that are accelerating back and forth more slowly than average. In sunlight, ultraviolet light is produced by charges that are accelerating back and forth more rapidly than average.
Impedance mismatch occurs when a wave, such as a sound wave, light wave, or electromagnetic wave, encounters a boundary between two materials with different acoustic, optical, or electromagnetic impedances. Impedance is a measure of how much a material resists the passage of a wave. When there is a significant difference in impedance between two materials, some portion of the wave is reflected back at the boundary.
The order of colors from shortest to longest wavelength: Violet < Blue < Green < Red
Violet light has the highest energy and shortest wavelength in the visible spectrum. It is even closer to ultraviolet (which starts just below 380 nm).
The energy of light is inversely proportional to its wavelength. This means that shorter wavelengths correspond to higher energy photons, and longer wavelengths correspond to lower energy photons.
The blue color of the sky is due to Rayleigh scattering, which occurs when sunlight interacts with the small particles and molecules in Earth’s atmosphere (e.g., oxygen and nitrogen molecules).
Even though violet light is scattered more than blue, the sky appears blue because:
The Sun emits more light in the blue region than in the violet region.
Our eyes are more sensitive to blue light than to violet light.
Why Sunsets and Sunrises Appear Red: During sunrise and sunset, the Sun is near the horizon, so sunlight has to travel through a longer path in the Earth's atmosphere compared to when it is overhead. Along this longer path, shorter wavelengths (blue and violet) are scattered out of the direct line of sight, leaving mostly longer wavelengths (red, orange, yellow) to reach your eyes.
Laser light is both coherent and monochromatic, meaning the light waves have the same wavelength and are in phase with one another. This allows the diffraction and interference effects to create a clear and structured pattern on the wall. Flashlight light is neither coherent nor monochromatic. It consists of many wavelengths (polychromatic light) and the light waves are not in phase with each other. This random nature prevents the formation of a well-defined interference pattern.
Dispersion occurs when light passes through a medium (like water droplets) and different wavelengths (colors) of light bend by different amounts due to their varying refractive indices. In a raindrop, this causes white sunlight to spread out into its component colors (red, orange, yellow, green, blue, indigo, violet), creating the spectrum of the rainbow. Once the light enters the raindrop, some of it is internally reflected off the inside surface of the drop. This reflection ensures that the light exits the droplet in the direction we observe the rainbow.
The number of internal reflections determines the type of rainbow:
Primary rainbow: One internal reflection.
Secondary rainbow: Two internal reflections (fainter and reversed colors).
Since ultraviolet (UV) light has a much shorter wavelength than infrared (IR) light, UV photons carry significantly more energy than IR photons.
In lead crystal, red light moves faster than violet light because red light has a longer wavelength and interacts less with the crystal lattice. Violet light, having a shorter wavelength, interacts more with the material, slowing it down and bending more sharply than red light.
Dispersion occurs because the refractive index of lead crystal varies with the wavelength of light. Shorter wavelengths (like violet) are slowed down more and refracted more strongly than longer wavelengths (like red).
Sugar appears white in air because light reflects and refracts at the interfaces between the sugar grains and the surrounding air. The significant difference in refractive index (impedance mismatch) between sugar and air causes light scattering, making the pile of sugar look white. When sugar is placed in water, the refractive index of water is much closer to that of sugar than air is. This reduces the impedance mismatch, meaning less light is reflected or scattered at the sugar-water interfaces. As a result, the sugar grains become transparent, and light passes through them more smoothly, making them appear clear.
Laser light is coherent, meaning the light waves have a constant phase relationship and travel in the same direction. This coherence ensures that the beam remains narrow and does not spread out significantly as it propagates. Coherent light waves combine constructively, maintaining a tight and well-defined beam over long distances. In contrast, light from a flashlight is incoherent (the waves have random phases), causing it to spread out quickly.
The human retina contains cone cells, which are responsible for color vision. There are three types of cone cells, each sensitive to a specific range of wavelengths corresponding to red, green, and blue light.
When you subtract blue from white light, you are left with the combination of the remaining colors, red and green. The combination of red and green light produces yellow in additive color mixing.
In an atom, electrons occupy specific energy levels or orbitals. These levels are quantized, meaning electrons can only exist at certain discrete energies. When an electron jumps down from a higher energy level to a lower energy level, the energy difference between the two levels is released as a photon of light.
A laser diode generates light through the process of electroluminescence in a semiconductor material. The wavelength (and thus the color) of the emitted light is determined by the band gap of the semiconductor material in the active region of the diode, which is typically located at the anode side of the laser.
White light is not emitted directly by the LED itself. Instead, white LEDs often use ultraviolet (UV) or blue LEDs combined with phosphors to produce white light. The LED emits UV or blue light, which is absorbed by the phosphor. The phosphor then re-emits light at longer wavelengths, combining with the original blue light to produce white light.
Laser light is coherent, meaning all the light waves are in phase and travel in the same direction. This results in a highly concentrated beam of energy that can damage the retina by focusing intense light on a small area. LED light is incoherent, meaning the light waves are out of phase and spread out. This diffused nature makes it much less likely to cause damage to the retina because the energy is dispersed over a larger area.