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White light is combination of all lights that are visible. They consist of visible lights that occur naturally or are produced artificially. White light comes above infrared light in electromagnetic spectrum in frequency range. Phenomenon of splitting of white light into its constituent seven colors on passing through a glass prism is called Dispersion of Light. Isaac Newton was the first to use a glass prism to obtain spectrum of sunlight. He tried to split colours of spectrum of white light further by using another similar prism.
Also, read: Human Eye and the Colourful World
| Table of Content |
Key Terms: Electromagnetic Spectrum, Sunlight, Infrared Light, Photosynthesis
Electromagnetic Spectrum
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Electromagnetic spectrum is the collection of various light waves. Furthermore, this spectrum consists of radiations like radio waves, microwaves, infrared waves, visible light waves, ultraviolet waves, x-rays and gamma rays. However, of all these kinds of light waves, only the visible light wave, also called the white light, is visible to the naked human eye.
Electromagnetic spectrum is often shown in the form of proper arrangement of the waves as mentioned above based on their wavelengths or frequencies. Moreover, electromagnetic radiations follow the rules of reflection and refraction and are also known to be transverse in nature.
Gamma Ray is the most powerful radiation of all the rays mentioned above in the electromagnetic spectrum. In fact, gamma-ray finds extensive uses in the medical field, like killing the cancer cells and to find out the abnormal functioning of the heart and brain.
Following is the table consisting of all the light waves in the electromagnetic spectrum along with their frequency range:
| Radiation | Frequency range in Hz |
| Gamma Rays | 1020 - 1024 |
| X-Rays | 1017 – 1020 |
| Ultraviolet | 1015 – 1017 |
| Visible | 4-7.5*1014 |
| Near-infrared | 1*1014 - 4*1014 |
| Infrared | 1013 – 1014 |
| Microwaves | 3*1011 – 1013 |
| Radio waves | < 3*1011 |
What is White Light?
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White light is spectrum of light waves that consist of all visible lights. Furthermore, electrons act upon white light and the nearby ranges of infrared rays through absorption and emission. During absorption and emission of white light and nearby infra-red rays, electrons in atoms and molecules undergo movement from one energy level to another. This chemical process is practically active in phenomena such as photosynthesis.
White light or visible light is an integral part of electromagnetic spectrum yet is just a small fraction of the entire spectrum. In fact, rainbow is the perfect example of appearance of all the colors that lie in white light range appearing simultaneously.
In frequency range, ultraviolet rays come just above violet rays of VIBGYOR and infra-red rays come just below red rays. It is, therefore, safe to understand that white light lies between ultraviolet rays and infra-red rays of electromagnetic spectrum.
Difference between White Light and Sunlight
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White light is called as white because it consists of Seven colors. Sunlight splits into seven colors: violet, indigo, blue, green, orange, and red. Here is a comparison table for White Light and Sunlight.
| White Light | Sunlight |
|---|---|
| White light consists of sunlight. | Sunlight is a part of shite light. |
| White light is the mixture of primary colours of green, red and blue from which all the other secondary colours are formed. | Sunlight is the mixture of all light ranges that come in the spectrum of Sun. |
| It is not necessary for the white light to have a continuous spectrum. In fact, when the hydrogen gas is energized, the white light that it emits has a discrete spectrum. | The Sunlight has a continuous spectrum. |
Things to Remember
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- White light is the combination of all the visible lights.
- The white light is considered to come above the infrared light in the electromagnetic spectrum in the frequency range.
- White light is the source of VIBGYOR that is the abbreviation for the colors Violet, Blue, Green, Yellow, Orange and Red.
- The electromagnetic spectrum is the collection of various light waves and radiations.
- In the electromagnetic spectrum, the Gamma Rays are said to be the most powerful radiations.
- White light lies between the ultraviolet rays and the infra-red rays of the electromagnetic spectrum.
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Sample Questions [Click Here for Sample Questions]
Ques. What is the difference between reflection and refraction? (2 marks)
Ans. Reflection is the process in which a light ray returns to the same medium after it strikes the plane of the surface. Refraction is when the light ray passes from one medium to another and experiences a slight deviation from its original path.
Ques. Explain the term reflected ray. Also, explain irregular reflection. (2 marks)
Ans. When the incident ray hits a surface, the light ray returns into the same medium. This return of the beam into the same medium is called the reflected ray. Irregular reflection is the process of light reflection in an asymmetric and uneven plane. The beam of light reflected in this case is not parallel. Therefore, it is called irregular reflection.
Ques. What is white light? Explain its concept. (3 marks)
Ans. White light is the spectrum of light waves that consist of all the visible lights. Furthermore, the electrons act upon the white light and the nearby ranges of the infrared rays in the form of absorption and emission. During the absorption and emission of white light and nearby infra-red rays, the electrons in atoms and molecules undergo movement from one energy level to another. This chemical process is practically active in phenomena such as photosynthesis.
Ques. What are the three important features of white lights? (3 marks)
Ans. Following are some of important features of white light:
- The frequency range of white light in the electromagnetic spectrum is 4-7.5*1014 Hz.
- White light is the combination of the primary colors, namely red, blue and green, from which all the other colors are derived.
- Of the 7 colors that appear during the dispersion of white light, violet has the maximum frequency and the red color has the minimum frequency.
Ques. Explain the concept of dispersion. (3 marks)
Ans. When the light passes through a prism, it gets scattered into the rays of different colors. This phenomenon is called dispersion. Furthermore, the scattering of light happens according to the wavelength or frequencies of the light.
The white light disperses into the colours of Violet, Indigo, Blue, Green, Yellow, Orange and Red. The red color has the maximum wavelength of these colors, while the violet has the minimum wavelength.
Ques. Explain the concept of the electromagnetic spectrum. (5 marks)
Ans. Electromagnetic spectrum is the collection of various light waves. Furthermore, this spectrum consists of radiations like radio waves, microwaves, infrared waves, visible light waves, ultraviolet waves, x-rays and gamma rays. However, of all these kinds of light waves, only the visible light wave, also called the white light, is visible to the naked eyes of human beings.
Following is the table consisting of all the light waves in the electromagnetic spectrum along with their frequency range:
| Radiation | Frequency range in Hz |
| Gamma Rays | 1020 - 1024 |
| X-Rays | 1017 – 1020 |
| Ultraviolet | 1015 – 1017 |
| Visible | 4-7.5*1014 |
| Near-infrared | 1*1014 - 4*1014 |
| Infrared | 1013 – 1014 |
| Microwaves | 3*1011 – 1013 |
| Radio waves | < 3*1011 |
Ques. State the laws of refraction of light. If the speed of light in vacuum is 3X108 ms-1, find the speed of light in a medium of absolute refractive index 1.5. (5 Marks) [CBSE 2014]
Ans. (a) Two laws of refraction of light are:
(i) Incident ray, refracted ray and normal at the point of coincidence, lie in the same plane.
(ii) Second law of refraction is also known as Snell's law of refraction and it states that: ratio of Sine of angle of incidence to sine of refraction is constant for a given pair of media. It establishes a relation between angle of incidence and angle of refraction.
It can be expressed mathematically as follows:
sin i/sin r = n
Given: The speed of light in vacuum is 3 x 108 ms-1
n = 1.5
As we know that refractive index is given by the ratio of speed of light in vacuum to the speed of light in the medium.
n =\(\frac{\text{Speed of light in vaccum}}{\text{Speed of light in medium}}\)
n = \(\frac{3 \times 10^8}{\text{Speed of light in medium}}\)
Speed of light in medium =\(\frac{3 \times 10^8}{1.5}\) = 2 x 108 m
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