How Does the Color Spectrum Work? Key Concepts for Chemistry Students
What Is Spectrum?
Before understanding the colour spectrum, let us try to understand what is a spectrum? A spectrum is an array of certain elements that have been arranged together in an order of increasing wavelength.
Now, a colour spectrum is an array of 7 colours namely VIBGYOR, arranged in an order of increasing frequencies. The phenomenon was first observed by the profound scientist, Isaac Newton. He observed a white beam of light as it passed through a glass prism. To his surprise, the light from the other side was split into 7 different colour spectrum wavelengths. He studied the phenomenon further before he brought it to the notice of the public in 1665.
Only after this, people started to believe that white light is composed of 7 different colour spectrum wavelengths, namely Violet, Indigo, Blue, Green, Yellow, Orange and Red. This led to the conclusion that " whenever light passes through a medium which is capable of absorbing and reflecting light, spectrum formation is observed".
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What Causes the Spectrum? Let's Dive Deeper!
Light has a characteristic property, called the wavelength of light. The wavelength of light differs from colour to colour. Each colour has a specific wavelength. The spectrum lies in the range of "Visible Spectrum" from wavelengths 700 Nm to 300 Nm. The visible spectrum is merely a small part of the vast electromagnetic spectrum. All the ranges of wavelengths are not visible to the human eye. The human eye can see the wavelengths only between 300 and 700 Newton Meter.
Proof of Newtonian Theory of Spectrum
No theory in Science is acceptable, without optimal proof that validates it. For this, Newton provided excellent proof. He took a wheel that consisted of multiple colours, something like this:
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Then, he rotated the wheel at an excessively high pace. As the speed of the wheel increased, all the colours appeared to merge into a single beam of white light. This merging of colours proved that white light is made of 7 different colours and when all these 7 colours merged, they formed a monochromatic white light. Through this simple experiment, Sir Isaac Newton managed to prove his theory of the spectral nature of light.
Some Interesting Facts of the Spectrum
What is colour? To a common man, the word colour would just mean whatever we see in our surroundings. However, in Class 10 Chemistry Colour Spectrum, we understand the scientific point of view and conclude that the meaning of "colour" is completely different. From the Science perspective, an object has a colour when it absorbs all the wavelengths except one particular wavelength. The wavelength which the object is unable to absorb is reflected back and hence, our eyes can perceive the colour of the object. Objects appear to be colourful only because of the phenomenon of reflection and absorption.
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So the colours you see above are just a result of the phenomenons of reflection and absorption! Sounds interesting, isn't it?
Phenomenons Around Us Based on Spectrum Formation of Light
Rainbow: As kids, all of us would have been extremely fascinated by rainbows. Have you ever pondered upon the science of rainbows? Rainbows are also a result of the scattering of light into its constituent colours. As we saw earlier, when a white beam of light is passed through a glass prism, it scatters into its constituent colours. In the case of rainbow formation, tiny droplets in the atmosphere act as little prisms. As the light passes through these water droplets, the light undergoes total internal reflection. Due to this, the white light splits into 7 different colours and forms a beautiful rainbow in the sky.
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The Colour Effect on a CD: Have you ever observed a CD? If you've keenly observed it, you'd have surely noticed how it reflects light and produces a multi-coloured effect. This is another result of the scattering of light into its constituent colour spectrum wavelengths. The CD is smooth and shiny, it has a tiny gap in between layers which acts as the reflective surface, hence causing the colour spectrum effect. If you haven't observed this effect, you should quickly grab a CD and take a look at it!
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Colour of the Sky: What do you think is the colour of the sky? Blue right? Most of us think that the sky is blue. However, the sky isn't coloured, it is colourless. The blue shade is because of the phenomenon of scattering of light. Blue light has the shortest wavelength and hence it gets scattered easily. Since blue light scatters more than all the other colours, it is the most prominent and therefore the sky appears to be blue.
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FAQs on Color Spectrum in Chemistry: Meaning, Causes & Newton's Theory
1. What is meant by the term ‘color spectrum’ in Chemistry?
In Chemistry, the color spectrum refers to the range of colors produced when light is separated into its constituent wavelengths. While the visible light spectrum (seen in a rainbow) is the most common example, the concept extends to the entire electromagnetic spectrum. It is crucial for understanding how atoms and molecules interact with light, leading to phenomena like emission and absorption spectra which are unique to each element.
2. What are the seven colors of the visible spectrum in order of increasing wavelength?
The seven colors of the visible spectrum, arranged in order from the shortest wavelength to the longest, are Violet, Indigo, Blue, Green, Yellow, Orange, and Red. A common mnemonic to remember this order is VIBGYOR. Red light has the longest wavelength (around 700 nm) and the lowest frequency, while violet light has the shortest wavelength (around 400 nm) and the highest frequency.
3. What is the classic experiment to observe the dispersion of white light into a color spectrum?
The classic experiment to observe the color spectrum uses a glass prism. The process is as follows:
A narrow beam of white light (like sunlight) is directed onto one of the rectangular faces of the prism.
As the light enters the denser medium of the prism, it refracts or bends. Because the refractive index of glass varies slightly for different wavelengths, each color bends at a slightly different angle.
When the separated colors emerge from the opposite face of the prism, they refract again, fanning out even more to form a distinct band of seven colors on a screen. This phenomenon is called dispersion.
4. Why does a prism create a color spectrum, but a flat glass window pane does not?
This difference is due to the geometry of the two objects. A prism has non-parallel faces. When light enters, it disperses into different colors. These colors then travel to the second face at different angles and exit in different directions, creating a visible spectrum. In contrast, a window pane has parallel faces. While the light does disperse upon entering the glass, the second parallel surface reverses the effect. It bends the separated colors back so they emerge parallel to each other, recombining to form white light again. The light is merely shifted sideways (lateral displacement), but a spectrum is not observed.
5. What is the difference between an emission spectrum and an absorption spectrum?
Both are fundamental tools in atomic studies, but they represent opposite processes:
An emission spectrum is produced when an atom in an excited state releases energy. It appears as a series of bright, discrete lines of specific colors (wavelengths) against a dark background. Each line corresponds to an electron falling from a higher energy level to a lower one.
An absorption spectrum is produced when white light passes through a substance (like a cool gas). The atoms absorb the exact wavelengths of light they would otherwise emit. This spectrum appears as a continuous rainbow with specific dark lines where the light has been absorbed. These dark lines match the bright lines of the element's emission spectrum.
6. How does the color spectrum concept help in identifying elements in distant stars?
The concept is crucial for the field of astrophysics. Every element has a unique 'fingerprint' in the form of its absorption spectrum. When we observe the light from a distant star, it has passed through the star's cooler, outer atmosphere. The elements in that atmosphere absorb specific wavelengths of light, creating dark lines (absorption lines) in the star's spectrum. By analysing the precise position of these dark lines, scientists can accurately determine the chemical composition of the star's atmosphere, even from millions of light-years away.
7. How does the visible light spectrum (VIBGYOR) differ from the primary and secondary colors used in art?
This is a common point of confusion. The two concepts relate to different color models:
The visible light spectrum (VIBGYOR) is based on the additive color model. Here, colors are components of light itself. The primary colors of light are Red, Green, and Blue (RGB). When you combine all colors of the spectrum, or the three primaries, you get white light.
Colors used in art (like paint or ink) are based on the subtractive color model. Here, colors are pigments that absorb certain wavelengths of light and reflect others. The traditional primary colors are Red, Yellow, and Blue (RYB). Combining these pigments subtracts more light, and mixing them all theoretically produces black.
