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A spectrum is defined as a set of wavelengths that is a characteristic of electromagnetic radiation which is produced or absorbed by a specific object, substance, atom, or molecule. The colors of the rainbow, infrared radiation, ultraviolet radiation, and x-ray are few examples of the same.
Typically, there are two individual classes of spectra:
i. Continuous Spectrum
ii. Discrete Spectrum
Continuous Spectrum Definition
For a continuous spectrum, the light is generally composed of a wide, continuous range of colors (or energies) but with discrete spectra, only bright or dark lines at very discrete and sharply defined colors (energies) are observed. Discrete spectra are further divided into 2 spectrums; Emission spectra and absorption spectra.
There are two forms of discrete spectra: emission spectrum ( or bright-line spectra) and absorption spectrum(or dark line spectra).
Emission Spectrum: When electromagnetic radiation interacts with atoms and molecules of matter, then the electrons present in these atoms absorb energy and move to a higher energy state, thus losing their stability. Now, to regain their stability, the electrons move from the higher energy state to their lower energy state. Thus, to complete this job, these atoms and molecules produce radiation in several regions of the electromagnetic spectrum. This spectrum of radiation produced by electrons in the excited state of atoms or molecules is termed as an emission spectrum.
Absorption Spectra: When a ray of white light falls on a prism it generally experiences refraction twice. First, when it travels from the rarer medium (that is air) to a denser medium (that is glass) and then again from the denser medium ( example; glass) to a rarer medium (example; air). Lastly, a band of colors called a spectrum is observed.
On observing this spectrum more thoroughly, it was found that the color having a smaller wavelength deviates the most and vice versa. Thus, a spectrum of colors ranging from red to violet is detected where the colour red has the longest wavelength and thus suffers the least deviation. This kind of spectrum formed is termed as a continuous spectrum.
How is a Continuous Spectrum Produced?
When Newton performed his famous experiment with a prism and sunlight, he observed that the Sun formed a “rainbow” of colors. This is called as a continuous spectrum. Therefore, light from the Sun, and any star, forms a continuous spectrum.
For example; The light produced by incandescent light bulbs is an example of a continuous spectrum. These types of bulbs give off light by using a very thin coil of metal, the filament, (generally tungsten).
The Chemistry Of Continuous Spectrum
To fully understand continuous spectrum chemistry, it is significant to study the electromagnetic spectrum. White light is a continuous spectrum but this is only a part of a larger electromagnetic spectrum which further comprises of radio waves, infrared rays, microwaves, ultraviolet, gamma rays, and x-rays.
Even the sun’s light is believed to be continuous since rainbows are observed after it rains. There are often gaps where nothing is visible when the light is examined in detail through a spectrometer. A truly continuous spectrum should not contain any gaps and finding gaps in the sun’s light is how researchers know what it is made of.
Continuous Spectrum Examples
Rainbow is commonly accepted as an example as it details all the colors (or wavelengths) from red to violet without any gaps. Though, the sun’s light is not an ideal example of a continuous spectrum as it often contains absorption gaps. A perfect example of a continuous spectrum can be shown when a ray of white light is passed through a prism in suitable lab environments. Other researchers have shown that heating up objects till they glow can also produce the spectrum. This is because atoms or molecules produce white light at glowing.
To produce a complete continuous spectrum, absorption and emission spectra are put together. An emission spectrum is the exact opposite of an absorption spectrum. An absorption spectrum displays a few wavelengths with certain colors missing whereas an emission spectrum only displays the colors which are missing in an absorption spectrum. Therefore, combining the two spectra would give us all the wavelengths that are required to form a continuous spectrum.
Continuous Spectrum vs Line Spectrum
The continuous spectrum contains no gaps however the line spectrum contains several gaps. both absorption and emission spectra are responsible for creating continuous and line spectra. The main difference between these two spectra is that continuous spectra have all the wavelengths whereas line spectrum contains only some of the wavelengths. Line spectrum can be produced in emission and absorption spectrum whereas continuous spectrum occurs only when both the spectra that is absorption and emission spectra of a single species are put together.
Continuous Spectrum Examples
Q1. A continuous spectrum is formed by which of the following;
A. Incandescent electric bulb
C. Hydrogen molecules
D. Sodium vapor lamp
A continuous spectrum is referred to as a beam of light in which all the wavelengths are present within a given limit. A continuous spectrum is primarily formed by thermal emission from a blackbody. Only certain wavelengths can be produced and absorbed by the atom when the energy levels in the atom are quantized. This can be further explained by Bohr’s Quantization Principle.
The sunlight and Incandescent light can produce a continuous spectrum as it mainly contains the photodissociation of hydride ions (or negatively charged hydrogen atoms). There are several ways by which a continuous spectrum is formed such as when a ray of white light is incident on a prism, a band of seven colors is observed or a rainbow formed in sunlight, however, heating of gas forms an emission spectrum as the gas molecules absorb heat energy and produce it in the surrounding.
Hence, options A and B are correct.
Continuous Spectrum Citations
- Influence of Continuous Spectrum Light on Morphological Traits and Leaf Anatomy of Hazelnut Plantlets. Front Plant Sci . 2019 Oct 24;10:1318.
- Continuous-Spectrum Infrared Illuminator for Camera-PPG in Darkness. Sensors (Basel) . 2020 May 27;20(11):3044.
- From period to quasiperiod to chaos: A continuous spectrum of orbits of charged particles trapped in a dipole magnetic field. Chaos . 2020 Dec;30(12):123108.