Absorption and emission spectrum | Differences and definition.

Absorption spectrum  

If you take a prism and pass white light through it, then white light splits into its constituent colours VIBGYOR, this is called dispersion of light. The band of colour you see is called spectrum. If you look loosely you see that the spectrum is continuous which means you cannot say at what point one colour changed into different colour. In a simple way this colours are merged into each other. This type of spectrum is called continuous spectrum.

Now, if white light is passed through a gas, then through a prism, you see some dark lines in the spectrum this type of spectrum is called absorption spectrum, because the gas is absorbing light of some specific frequency.

Why it absorbs?

Because the molecules and atoms present in the gas absorb light of specific energy. Now, considering the fact that light behaves as a particle and single particle is called a photon, which is in the form of packets of energy. As energy is equal to planck's constant times the frequency of the light. Given by the formula

                                  E = h × μ

Energy associated with those disappearing frequencies are absorbed by the atoms or molecules of that gas. 

Definition 

When white light is passed through unexcited atomic hydrogen and then through a slit and prism, the transmitted light is lacking in intensity at the same wavelength as emitted in the corresponding emission spectrum.

Emission spectrum

Here white light is passed through an excited gas then through a prism, you see some lines on spectrum of some frequency and other frequencies of light has been disappeared. This type of spectrum is called emission spectrum because gas is emitting light of some specific frequency.

Why it emits?

Because, atoms and molecules present in the gas is emitting light of specific energy. when atoms and molecules moves from excited stage to ground stage in this process energy is released, that energy is emitted in the form of photon. As energy is equal to planck's constant times the frequency of the light. Given by the formula

                                 E = h × μ 

You can take this as fingerprint of material when light has passed through it. There is not always same pattern for every material. A fun fact is, with the idea of absorption and emission of spectrum it was understood that sun contains helium.

Definition

The spectrum of radiation emitted by a substance that has absorbed energy is called an emission spectrum.