Optics #1 _ Understanding The Emission Of Visible Light In Relation With Excitation of Electrons

in stemng •  2 months ago

Introduction

Optics is the study of the behavior and characteristics of light; reflection, refraction, interference, emission, polarization, photoelectric effect, Compton effect and everything about light. Light is an electromagnetic radiation within the range of the electromagnetic spectrum and filled with photons; photon energy is responsible for light.
From the time the earth started existing till now, light has played vital role in the ecosystem. The light from the sun serves some agricultural purposes like as source of energy for photosynthesis necessary for production of food by plants


Image credits:CC by SA 2.0|| Source: Wikimedia

This same light from the sun also causes illumination(this is the reason we can see and tell even the color of a leaf) and a source of energy for almost everything; both living and non-living on earth.

Illumination seen on the earth due to reflected light from the sun, made the human race be in a constant fight against darkness. Humans have seen how marvelous the light from the sun is and its illumination purpose which is responsible for sight, and have desired to remain in that kind of light constantly. However, this light from the sun is not always available in any geographical location at all time due to rotation or spinning of the earth round the sun, night would surely surface and darkness is bound to exist at some certain times in any location, but humans desire to light up their environment anytime. Hence, man started searching for an artificial means to illuminate his environment even in the dark; a source of illumination he can control at his will. This led humans to burning some woods or even grasses as a source of illumination and warmth. Later, with the discovery of hydrocarbons as a source of energy, humans started using kerosene lamp for illumination. Phase shifted entirely with the evolution of electricity. Thanks to Sir Benjamin Franklin who first discovered electricity, a natural occurring phenomenon that has been in existence.

Explanation of Optics



Image credits: CCA 2.0|| source: Wikimedia|| Author: Giorgio Brida

Optics is s branch of physics that deals with the behavior and properties of light as it interacts with matter and the production of instruments or devices that work with light or can detect light such as photo-sensors, lenses, solar panel, photovoltaic cell and other similar things.

The word optics is derived from the Greek term τα ὀπτικά meaning "appearance or look"ref
Optics typically deals with the behavior of visible light, infrared light and ultraviolet light. Other electromagnetic radiation like x-rays, gamma rays, micro waves and radio waves exhibit similar characteristics with light. Optics can be classified into classical optics and modern optics.

  • Classical optics: This is further divided into two which are geometric or rays optics in which light is assumed to be a collection of rays travelling in a straight line and changes direction when it pass through surfaces(refraction) or reflect from surfaces; physical or wave optics in the other hand considers light as an electromagnetic wave, this accounts for the diffraction and interference properties of light which could not be explained by the geometric optics. The geometric-optics was first developed before the physical-optics

Image credits:CC by SA 3.0| Source: Wikimedia
  • Modern optics: Optical science and optical Engineering are the two main branches of modern optics. In optical science, the electromagnetic and quantum properties of light is studied while optical engineering is the application of optics. Conversely, optical science is a theoretical approach to modern optics while optics Engineering is a practically approach to modern optics. However, both optical science and optical Engineering are vital. The major goals of scientist is to produce things that would help make life worth living for man, to achieve this goal, theoretical knowledge is thus necessary, because their is no way to produce what is useful without theoretical approach. So, it is theory before practical. The reverse might be dangerous.

Quantum optics a subclass of modern optics which uses both classical physics and quantum-mechanical physics, to study the behavior of light in submicroscopic level. Quantum optics founds application in light detectors, electronic image sensors, photo-voltaic cells, lasers and so on

Brief history of Optics

To know the future of something, it is essential to study the history. History is like a pathway to analyze the future of anything. Hence, studying the emergence of optics can give us a proper analysis on what the future of optics would look like.
Optics started with the evolution of lens by the ancient Egyptians and Mesopotamians with the first made lens (Nimrud leans) being made from polished crystal, usually quartz as far back as 700BC ; theories of light and vision by Greek philosophers; and the development of geometric optics in the Greco-Roman world ref
With the discovery of electricity, scientists knew that they can harness this electric energy as photon energy; a source of illumination as given in law of conservation of energy. Hence, came the invention of electric lamp by Humphrey Davy In 1802ref who after experimenting with electricity created an electric battery; he further connect a piece of carbon to his battery using wires, this circuit caused the carbon to glow, and therefore producing light. His electric lamp was known as electric arc lamp, it has setbacks of short life span, excess heat, too much brightness and giving off smoke which might cause pollution.
The evolution of electric lamp widened the horizon of optics, hence making scientists gain in-depth knowledge on the behavior of light. Today, optic is even a course offered in tertiary institutions.



Most times we see visible light radiate. But little do we care to know the chemistry or physics behind this emission of light; to understand properly, how visible light is emitted by atoms, a knowledge of two fundamental laws in science is required: the law of conservation of energy(law of thermodynamics) and Newton's first law of motion . Also understanding the excitation and relaxation of electrons is vital_Quantum Physics

Excitation of Electron

The emission of light basically relies on two major laws: the law of conservation of energy(law of thermodynamics) and Newton's law of motion.
According to Newton's second law of motion, an object would continue in its state of motion unless propelled by an external unbalanced force. In an atom, the electrons are in a state of rest or uniform motion until an external force or energy acts upon it. When this external energy is introduced to an atom, its electrons absorbs this energy and become excited_ energy must be conserved, therefore, the energy absorbed by this electron is converted into kinetic energy
Excitation is the movement or transfer of bound electron from lower energy level or ground state closer to the nucleus to an higher energy level, a position farther from the nucleus. Excitation can be achieved typically in three ways: photoexcitation(PE), electrical excitation(EE) and thermal excitation.


Image Credits: Public Domain||Source: Wikimedia|| Author: A. Carlson

In photoexcitation(PE), the electrons in an atom absorbs the energy of an external photons incident on it and becomes excited if this energy is greater than the work function of the bound electron_Einstein's law of photoelectricity. In electrical excitation(EE), the electrons of the atom collides with an energetic electron from electricity , receives its whole energy from that energetic flowing electrons(electricity) and becomes excited. While in thermal excitation, heating to higher temperature causes lattice vibration which provides sufficient energy to transfer bound electron from lower energy level to a higher energy level. Higher temperatures implies a higher kinetic energy of electron and molecules of an atom.

In any means used to achieve excitation, an external energy causes motion of the electrons of the atom according to Newton's law. This electrons absorbs the excitation energy and converts it to kinetic energy; hence motion of electron_energy must be conserved in relation with law of conservation of energy.

Emission of Light

Excitation of electrons is unstable, if this excited electrons do not completely escape from the shells of its atom, it would fall back to its initial energy level or orbital; this is known as electron relaxation. When excited electrons passes through relaxation, it gives off some energy just like lightning bolt gives off energy. As this electrons jumps from higher energy level to a lower energy level, it gives off photons as the bye-product which is responsible for light.


Image credits:CC by SA 3.0| Source: Wikimedia
The energy of this emitted photon is the energy difference between the initial energy level of the electron and the present energy level of the electron within an atom
hf= E2 -E1
w=c/f
where
h= Planck's constant
c= speed of light
f= frequency of emitted photons
w= wavelength of emitted photons

If the wavelength of the photons is in the range of 390-700nm, the radiation is visible light. If the wavelength is below 390nm, the radiation is infrared and finally if the wavelength is above 700nm, the radiation is ultraviolet.
Whenever photons are emitted by atoms due to excited electron falling back to initial lower energy level, radiation exits, which can be visible light or otherwise according to its wavelength.
When firewood is set ablaze, the heat energy from the fire is introduced to the wood. If fire is intense, the firewood would give a reddish glow which is visible to the sight, but if the fire is minimal, the glow would be unnoticed. We can say that when the fire is intense, the heat energy increases; thus, increasing the frequency of the photons to the frequency of visible light according to the relation E=hf


Image credits:CC by SA 2.0| Source: Wikimedia Author: Jeff Kubina

But when the heat energy from the fire is too much, the wood would burn off quickly.
Similarly, when metal is heated to a certain temperature, the electron and molecules of the metal gains kinetic energy and would further jump to a higher energy level. Due to instability of excitation, this excited electrons falls back to its actual orbits if it does not eject completely from its atom; thus emitting photons. This is the reason metal give a reddish glow visible in a dark room while charged with fire.

Conclusion

The principle of emission of light basically can be conclude with two scientific laws: Newton's first law of motion and the law of conservation of energy. The electrons in an atom is caused to change its uniform motion by an external force(energy), this energy is absorbed by the electrons of this atom making the electrons excited, so the initial energy is converted to kinetic energy causing movement of electrons. This excited electrons would after jump back to lower energy level emitting photons(light). Subsequently, this kinetic energy of the electrons is converted to photon energy.

Image credits: CC by SA 3.0||Source: Wikimedia|| Author: Kurzon.

Finally, how light is produced is summarized in the diagram above. External energy hits the electron of an atom and pushes it to excitation. After some moments this excited electron would fall back to lower energy level and in the process emits photons which is the particles of light


References

Thanks for your ample time, I remain your brethren @ikchris


If you publish STEM(Science, Technology, Engineering, Mathematics) related articles, consider using #steemstem in your tags, include #stemng if you reside in Nigeria. Check out @stemng blog to read fascinating publishes

Authors get paid when people like you upvote their post.
If you enjoyed what you read here, create your account today and start earning FREE STEEM!
Sort Order:  

The gif embedded in the summary aptly captured the article in detail. Thanks for helping us understand the whole mystery of optics and concept of light illumination.

·

Welcom @olamseu
Am glad you learnt

Congratulations @ikchris! You have completed the following achievement on the Steem blockchain and have been rewarded with new badge(s) :

Award for the number of posts published

Click on the badge to view your Board of Honor.
If you no longer want to receive notifications, reply to this comment with the word STOP

To support your work, I also upvoted your post!

Do not miss the last post from @steemitboard:

SteemitBoard - Witness Update
SteemFest³ - SteemitBoard support the Travel Reimbursement Fund.

Support SteemitBoard's project! Vote for its witness and get one more award!



This post has been voted on by the steemstem curation team and voting trail.

There is more to SteemSTEM than just writing posts, check here for some more tips on being a community member. You can also join our discord here to get to know the rest of the community!

Hi @ikchris!

Your post was upvoted by utopian.io in cooperation with steemstem - supporting knowledge, innovation and technological advancement on the Steem Blockchain.

Contribute to Open Source with utopian.io

Learn how to contribute on our website and join the new open source economy.

Want to chat? Join the Utopian Community on Discord https://discord.gg/h52nFrV



This post has been voted on by the steemstem curation team and voting trail.

There is more to SteemSTEM than just writing posts, check here for some more tips on being a community member. You can also join our discord here to get to know the rest of the community!

Congratulations @ikchris! You have completed the following achievement on the Steem blockchain and have been rewarded with new badge(s) :

Award for the number of comments received

Click on the badge to view your Board of Honor.
If you no longer want to receive notifications, reply to this comment with the word STOP

Do not miss the last post from @steemitboard:

SteemitBoard - Witness Update
SteemFest³ - SteemitBoard support the Travel Reimbursement Fund.

Support SteemitBoard's project! Vote for its witness and get one more award!