Difference Between Achromatic and Monochromatic

Achromatic vs Monochromatic
 

Achromatic and monochromatic are two important terms used in electromagnetic theory, optics, and other fields of physics. These two terms have a close connection with colors of the electromagnetic spectrum. In this article, we are going to discuss what achromatic and monochromatic are, their definitions, similarities, and finally the difference between achromatic and monochromatic.

What is Monochromatic?

The term “mono” refers to a singular object or subject. The term “chrome” refers to colors. The term “monochrome” is a reference to a single color. To understand monochromatic, one must first understand the electromagnetic spectrum. Electromagnetic waves are classified into several regions according to their energy. X-rays, ultraviolet, infrared, visible, radio waves are to name a few of them. Everything we see is seen due to the visible region of the electromagnetic spectrum. A spectrum is the plot of intensity versus energy of the electromagnetic rays. The energy can also be represented in wavelength or frequency. A continuous spectrum is a spectrum in which all the wavelengths of the selected region have intensities. The perfect white light is a continuous spectrum over the visible region. It must be noted that, in practice, it is virtually impossible to obtain a perfect continuous spectrum. An absorption spectrum is the spectrum obtained after sending a continuous spectrum through some material. An emission spectrum is the spectrum obtained after the continuous spectrum is removed after the excitation of the electrons in the absorption spectrum.

Absorption spectrum and emission spectrum are very useful in finding chemical compositions of materials. The absorption or emission spectrum of a substance is unique to the substance. Since the quantum theory suggests that the energy must be quantized, the frequency of the photon determines the energy of the photon. Since energy is discrete, the frequency is not a continuous variable. Frequency is a discrete variable. The color of a photon incident on the eye is determined by the energy of the photon. A ray having only photons of a single frequency is known as a monochromatic ray. Such a ray carries a beam of photons, which are same in color thus getting the term “monochromatic”.

What is Achromatic?

The usage of “a” on the beginning of a word means the negation of the term. Since “chrome” means colors, “achromatic” means without any color. An achromatic lens is a lens which is capable of refracting the light coming through it without dividing it to colors. Such lenses consist of complex, compound lens systems. These lenses are used as a correction for chromatic aberration. Neutral colors such as grey are known as achromatic colors.