Difference Between Emission and Absorption Spectra

Introduction

When an electron oscillates with a focal point (or molecular dipole oscillates), it generates electromagnetic waves. The ratio of the electric and magnetic fields in any medium is equal to the velocity of the electromagnetic wave propagating in that medium. The speed of light in a medium is less than the speed of light in a vacuum. The energy of the electromagnetic wave is from the energy of the oscillating electrons available. When an object burns it emits colors.

That is, the object emits electromagnetic radiation. It depends on the temperature. When an object is heated, it begins to glow red as it warms up. And the object glows a pure orange when heated continuously. Also glows white when heated.

Fig:1 Emission spectra

What are Emission Spectra?

When white light passes through a prism it can be calculated as a continuous spectrum on a screen that splits into seven colors. The name for this process is the color spectrum of light. The spectrum is the set of colors obtained on the screen by the color spectrum. When it comes to more than one spectrum it is called the electromagnetic spectrum. The spectrum can be divided into two types, the emission spectrum, and the absorption spectrum.

The spectrum derived from the luminous source is the self-luminous emission spectrum. Each light source has a unique emission spectrum.

Types of Emission Spectra

The emission spectrum can be divided into three types.

• Line emission spectrum

• Continuous emission spectrum

• Band emission spectrum

Line Emission Spectrum

The line spectrum is obtained when high-temperature gas is passed through a prism. The line spectrum can also be called the not continuous spectrum. This spectrum has sharp lines with finite wavelengths or frequencies. These spectra are emitted by agitated molecules or ions. Each line reflects the unique properties of the elements.

Continuous Emission Spectrum

When light from an incandescent lamp passes through a prism it splits into seven colors. That is it has every wavelength of all visible colors from violet to red. Fluorescent solids and liquids also give a continuous spectrum.

Band Emission Spectrum

In the band spectrum the most numerous, closest spectrum lines overlap one another to form specific bands. These bands are darkly divided, these spectrums are called band spectrums. In this spectrum, one side of the band is sharp (high luminosity) and dim on the other side(low luminosity).

Characteristics of the Emission Spectra

• Continuous emission spectra depend on the temperature of the light source.

• It is independent of the properties of the light source.

• Each line in the line emission spectra reflects the unique properties of the emitting elements

• Band emission spectrum depends on the properties of molecules.

What are Absorption Spectra?

The absorption spectrum is the spectrum of light transmitted through an absorbing object or medium and obtained from it. This spectrum has the properties of absorbing material. It is classified into three types.

Characteristics of Absorption Spectra

• The absorption spectrum depends on the properties of absorbed elements.

• The continuous absorption spectrum absorbs all other colors except the color of the glass which is placed in front of the glass source.

• Mostly gases are used as absorption spectra. For example, sodium and iodine gases produce an absorption spectrum.

Types of Absorption Spectra

There are three types of absorption spectra.

Continuous Absorption Spectrum

By passing light through the medium and then passing that light through the prism, the light spectrum is reached and from it, the continuous absorption spectrum is obtained. For example, if white light is transmitted through blue glass, the mirror will absorb all other colors except blue.

Line Absorption Spectrum

The line absorption spectrum is the spectrum obtained by the transmission of light from a fluorescent light bulb through a cooled gas (medium). Similarly, in the spectrum obtained after the sodium vapors were emitted, the light coming from the carbon emitter, two black lines appear on the yellow side of the series spectrum. These are the line absorption spectrum of sodium gases.

Band Absorption Spectrum

In the spectrum obtained after exposing white light to iodine gases, black bands appear on a bright white background. These black bands are band absorption spectrum. Similarly, band absorption spectra can be obtained when white light is transmitted through diluted blood, plant chlorophyll, mineral, or organic solution.

Applications of Emission Spectra

Emission spectra change for each element in the periodic table. So we can determine the combination of the elements. The emission spectrum is also used in the chemical analysis of elements. When the elements are heated we can see the emission spectrum of the element. So this property is used to differentiate the elements based on emission spectrum. Emission spectroscopy is the major application of emission spectra.

Conclusion

The orderly distribution of electromagnetic waves based on their wavelength or frequency is called the electromagnetic spectrum. When white light passes through a prism it can be calculated as a continuous spectrum on a screen that splits into seven colors. The name for this process is the color spectrum of light. The spectrum is the set of colors obtained on the screen by the color spectrum.

When it comes to more than one spectrum it is called the electromagnetic spectrum. The spectrum can be divided into two types, the emission spectrum, and the absorption spectrum. The spectrum derived from the luminous source is the self-luminous emission spectrum. The absorption spectrum is the spectrum of light transmitted through an absorbing object or medium and obtained from it. Each line in the line emission spectra reflects the unique properties of the emitting elements. The absorption spectrum depends on the properties of absorbed elements.

FAQs

Q1. What are Fraunhofer lines?

Ans: Spectrum observed from the sun when examined, several black lines are found in that spectrum (line absorption spectrum). These black lines found in the solar spectrum are called Fraunhofer lines.

Q2. What is the use of visible light?

Ans: Visible light is used to study the molecular structure, to understand the structure of electrons in the outer shell of atoms, and to give the eyes a sense of sight.

Q3. Give any three properties of electromagnetic waves?

Ans:

• No medium is required for electromagnetic waves to propagate. Therefore, the electromagnetic wave is not a mechanical wave.

• Electromagnetic waves are not deflected by the electric field and the magnetic field.

• The intensity of an electromagnetic wave is the energy that passes through a unit area perpendicular to the direction of the electromagnetic wave.

Q4. What are infrared rays?

Ans: Infrared rays are generated by heat sources ( also called heat waves). Infrared rays are also generated when molecules undergo rotational motion or vibration.

Q5. Describe the concept of electromagnetic wave concentration

Ans: The intensity of an electromagnetic wave is the energy that passes through a unit area perpendicular to the direction of the electromagnetic wave.