What determines the color of light? Describe the difference between red light and blue light.

When we discuss the color of light, we're referring to a specific characteristic of electromagnetic radiation that the human eye can detect. Light exhibits wave-like properties, and two key descriptors of these waves are wavelength and frequency. The wavelength is the distance between successive peaks of a wave and is typically measured in nanometers (nm). On the other hand, frequency refers to the number of wave cycles that pass a given point per second, measured in Hertz (Hz).

The relationship between wavelength and frequency is inversely proportional, as described by the equation \( c = \lambda u \) where \(c\) is the speed of light, \(\lambda\) is the wavelength, and \(u\) is the frequency. When the wavelength increases, the frequency decreases, and vice versa. This relationship helps explain why different colors of light have distinct properties. For example, red light, with its longer wavelengths, has lower frequency, while blue light, with its shorter wavelengths, has higher frequency.

The visible spectrum is the portion of the electromagnetic spectrum that can be seen by the human eye. It ranges approximately from 380 nm to 750 nm. The light within this spectrum is what we perceive as color. Starting from the shorter wavelengths, we encounter violet, blue, green, yellow, orange, and red. The order of colors is the same one found in a rainbow and can be remembered by the acronym 'ROYGBIV'.

Different colors within the visible spectrum are associated with varying wavelengths, with violet on the one end (approx. 380-450 nm) and red on the other (approx. 620-750 nm). As a result, each color we see in the world around us corresponds to a specific wavelength range within the visible spectrum. The color transition across the spectrum is continuous, meaning there are no abrupt changes from one color to the next, but rather a gradual shift through myriad hues.

The concept of electromagnetic radiation (EMR) encompasses a broad range of wavelengths and frequencies. EMR is a form of energy that travels through space at the speed of light, manifesting as both waves and particles called photons. The electromagnetic spectrum includes not only visible light but also other types of waves such as radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays. Visible light is just a small part of this vast spectrum.

Each type of electromagnetic radiation has a different range of wavelengths and, accordingly, energy levels. Radio waves have the longest wavelengths and lowest energy, while gamma rays have the shortest wavelengths and highest energy. The visible spectrum, sitting between infrared and ultraviolet, allows humans to perceive the world in color. EMR travels in vacuum with a speed of \(c\), which is roughly 299,792,458 meters per second, and this speed is a fundamental constant of nature.