Color Spectrum

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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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FAQ (Frequently Asked Questions)

Q1. How to Observe the 7 Constituent Colours of Light?

Ans. The glass prism method is one of the best experiments for observing the dispersion of light. To perform the experiment, follow the steps given below:

  • Firstly take a glass prism, be careful not to drop it by mistake. 

  • Take a monochromatic source of light and pass it through one of the faces of the prism. 

  • Once you pass it through the prism, a spectrum of 7 different colours appears from the other face.

This proves that light consists of 7 different colours and disperse when passed through a glass prism. 

Q2. Why Does Dispersion of Light Not Happen When Light Passes Through a Windowpane but the Dispersion Happens When the Same Monochromatic Light Passes through a Prism?

Ans. When monochromatic light passes through a glass prism, it splits into its constituent colours. However the same doesn't happen when light passes through a flat window pane. This is because of the peculiar structure of the glass prism. In a glass prism, the opposite sides are not parallel to each other. When light strikes the first surface, it undergoes refraction since glass is denser than air. The amount of bending of light depends on its wavelength. Because the opposite faces of a prism are not parallel, each wavelength of light emerges with a different bend and not parallelly. Whereas in the case of the windowpane, both the surfaces are parallel to each other and hence dispersion of light is not observed.