1. Atomic emission spectrum

2. When a sample of gaseous atoms of an element at low pressure is subjected to an input of energy, such as from an electric discharge, the atoms are themselves found to emit electromagnetic radiation.
On passing through a very thin slit and then through a prism the light (electromagnetic radiation) emitted by the excited atoms is separated into its component frequencies.

3. The familiar dispersion of white light is illustrated below:

4. Solids, liquids and dense gases glow at high temperatures
Solids, liquids and dense gases glow at high temperatures. The emitted light, examined using a spectroscope, consists of a continuous band of colours as in a rainbow. A continuous spectrum is observed. This is typical of matter in which the atoms are packed closely together. Gases at low pressure behave quite differently.
The excited atoms emit only certain frequencies, and when these are placed as discreet lines along a frequency scale an atomic emission spectrum is formed.

5. The spectral lines in the visible region of the atomic emission spectrum of barium are shown below.

6. The atomic emission spectrum of an element is the set of frequencies of the electromagnetic waves emitted by atoms of that element. Each atom's atomic emission spectrum is unique and can be used to determine if that element is part of an unknown compound.
Light consists of Electromagnetic radiation of different wavelengths. Therefore, when the elements or their compounds are heated either on a flame or by an electric arc they emit energy in form of light. Analysis, of this light, with the help of spectroscope gives us a discontinuous spectrum. A spectroscope or a spectrometer is a instrument which is used for separating the components of light, which have different wavelengths. The spectrum appears in a series of line called line spectrum

7. This line spectrum is also called the Atomic Spectrum because it originates in the element. Each element has a different atomic spectrum.The production of line spectra by the atoms of an element, indicates that an atom can radiate only certain amount of energy. This leads to the conclusion that electrons cannot have any amount of energy but only a certain amount of energy.
The emission spectrum characteristics of some elements are plainly visible to the naked eye when these elements are heated. For example, when platinum wire is dipped into a strontium nitrate solution and then inserted into a flame, the strontium atoms emit a red color. Similarly, when copper is inserted into a flame, the flame becomes green. These definite characteristics allow elements to be identified by their atomic emission spectrum. Not all lights emitted by the spectrum are viewable to the naked eye, it also includes ultra violet rays and infra red lighting.

8. The fact that only certain colors appear in an element's atomic emission spectrum means that only certain frequencies of light are emitted. Each of these frequencies are related to energy by the formula:
herein E is energy, h is Planck's constant and ν is the frequency. This concludes that only photons having certain energies are emitted by the atom. The principle of the atomic emission spectrum explains the varied colors in neon signs, as well as chemical flame test results mentioned above. Each of these frequencies are related to energy by the formula: .
The frequencies of light that an atom can emit are dependent on states the electrons can be in. When excited, an electron moves to a higher energy level/orbital. When the electron falls back to its ground level the light is emitted.
An emission spectrum is always the inverse of its absorption spectrum.

9. . Emission spectrum of Hydrogen
An emission spectrum is always the inverse of its absorption spectrum.
Emission spectrum of Hydrogen