We know that light is electromagnetic radiation composed of several frequencies of radiations. An ordinary light features a wide range of wavelengths with respective frequencies. Electromagnetic waves can travel in a vacuum at the speed of light. The electromagnetic spectrum includes a wide range of electromagnetic radiation, which includes many subranges that are known as portions, like ultraviolet rays or visible light. Microwaves, infrared light, ultraviolet light, X-rays and gamma-rays are some of the types of radiation included in the electromagnetic spectrum.
When the white light is passed through a medium, they get split according to their respective frequencies and wavelengths. The white light spectrum starts from 7.5 x 10^14 Hz for the violet colour to 4 x 10^14 Hz for the red colour. The interaction of electromagnetic radiation with matter causes the molecules and atoms present in a matter to absorb energy and reach a higher energy state. This higher energy state is unstable, and hence they have to emit energy in the form of radiations to return to their original states. This process generates emission spectra and absorption spectra.
Let us know more about spectra and various types, along with their applications.
Spectra and Spectroscopy
The plural form of spectra is a spectrum. Spectrum is widely used in the field of optics and in many more fields. Spectrum features a wide range of wavelengths of different frequency radiations. A rainbow is a spectrum that constitutes different wavelengths of light. The spectrum of light from the rainbow is commonly referred to as VIBGYOR. The prism is also an ideal example to describe the spectrum of radiation. When the white light passes through the prism, it gets separated into different wavelengths of light known as spectrum.
The instrument which is used to separate the radiations of different wavelengths is known as a Spectroscope or Spectrograph. A spectrometer is a scientific device that aids to separate and measure spectral components of a physical phenomenon. Branch of science that deals with the study of the spectrum is known as spectroscopy.
Spectrograph features a prism or diffraction grating that is used to disperse light. The emerging light after the dispersion from the prism is examined using a photographic film.
Spectra is classified into two types:
- Emission spectra
- Absorption spectra
The emission spectrum is formed by the radiation emitted by electrons in the excited molecules or atoms is known as the emission spectrum. The emission spectrum comprises frequencies of electromagnetic radiation due to the influence of chemical elements or chemical compounds emitted due to an atom or molecule, which make the transition from a high energy state to a lower energy state. These excited electrons have to radiate energy to return to ground states from the excited state, which is unstable. The emission spectrum is formed by the frequencies of these emitted light.
Based on the source, the emission spectrum is classified into two types:
- Continuous spectrum
- Line spectrum
This kind of spectrum is constituted by the frequencies of light transmitted with dark bands when energy is absorbed by the electrons in the ground state to reach higher energy states. This type of spectrum is produced when atoms absorb energy. Let’s know how absorption spectra are formed.
When light from any source is passed through the solution or vapour of a chemical, a pattern comprising dark lines is obtained. This pattern is analysed using the spectroscope. Depending on the nature of the chemical or element, certain radiation is absorbed by the chemical or element when passed through it.
The dark line pattern is seen exactly in the same place where coloured lines are seen in the emission spectrum. The spectrum thus obtained is known as the absorption spectrum.
Emission spectra can emit all the colours in an electromagnetic spectrum, while the absorption spectrum can have a few colours missing due to the redirection of absorbed photons. The wavelengths of light absorbed is helpful in figuring out the number of substances in the sample.
The pattern of absorption lines, emission lines and the continuous spectrum are as shown in the figure below.
Read more about the emission spectrum.
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Frequently Asked Questions on Absorption Spectrum
1. How is the emission spectrum used?
Emission spectrum is used to understand the composition of the chemicals.
2. Which type of spectrum comprises dark lines or gaps in the spectrum?
3. This spectrum of radiation emitted by electrons in the excited atoms or molecules is known as?
4. What is Atomic spectra?
The study of atoms (and atomic ions) through their interaction with electromagnetic radiation.
5. What is spectroscopy?
Branch of science that deals with the study of spectrum.