Question

Describe how white light interacts with a colored substance to make it look colored.

Short answer

White light is composed of multiple colors. A colored substance absorbs some wavelengths of white light and reflects others. The reflected wavelengths determine the color we perceive.

Step-by-step solution

Understanding white light composition

White light from sources such as the sun or light bulbs is composed of various colors, which together appear as white. This is because white light contains all the visible wavelengths of light in the spectrum. Each color has a different wavelength, with violet having the shortest wavelength and red having the longest.

Interaction with a colored substance

When white light encounters a colored substance, some of the wavelengths of the light are absorbed by the substance, while others are reflected or transmitted. The specific wavelengths that are absorbed depend on the properties of the substance. The wavelengths that are not absorbed are what we end up seeing.

Perception of color

The color of the substance is determined by the light that is reflected or transmitted to our eyes. If a substance absorbs all the colors except for red, it will appear red because that is the color that is reflected and perceived by our eyes. If it reflects all colors equally, it will appear white or clear to us.

Key concepts

White Light Composition

White light is akin to a symphony of colors, each playing its distinct wavelength to create a harmonious illusion of whiteness. When we observe sunlight or the light emanating from a light bulb, we are witnessing the convergence of all visible wavelengths in the spectrum. Imagine white light as a paintbox that contains the full range of colors that the human eye can perceive. Violet, indigo, blue, green, yellow, orange, and red; each color represents a slice of the visible spectrum, with violet having the shortest wavelength and red boasting the longest.

Wavelengths of Light

Delving into wavelengths of light is to study the very threads that weave the vibrant tapestry of our visual world. Wavelengths are essentially the distance between consecutive peaks of a light wave. They are usually measured in nanometers (nm), with one nanometer being one billionth of a meter. The spectrum of visible light ranges approximately from 380 nm (violet) to about 700 nm (red). Each color we perceive in this range has its unique wavelength, dictating its position in the spectrum. For instance, blue light has a wavelength of about 450-495 nm, whereas yellow light falls in the 570-590 nm region.

Perception of Color

The tapestry of color that unfolds before our eyes is a complex interaction between light and the physiology of sight. Our perception of color is a phenomenon that occurs when the wavelengths of reflected or transmitted light reach our eyes, processed by the brain through signals sent from the cells in our retinas. Rods and cones are the two types of photoreceptor cells, with cones being responsible for color vision. The cones are further divided into three types, each sensitive to different wavelengths corresponding to red, green, or blue. Thus, when a substance reflects only red light (around 620-750 nm), it triggers the corresponding cones, and we perceive the object as red.

Light Absorption and Reflection

When pondering why certain objects dazzle with color while others are cloaked in shadow, we consider the roles of light absorption and reflection. Substances absorb light waves based on their molecular structure, which dictates which wavelengths they will seize and which they will spurn. The absorbed light is converted into other forms of energy, typically heat. On the flip side of absorption is reflection, the process by which certain wavelengths evade capture and bounce off the substance. The reflected light is what conveys the object's color to our eyes. A red apple, for instance, absorbs all the other colors of the spectrum but reflects red, casting its tempting hue to the beholder.