The Photoelectric Effect.

    A process known as the photoelectric effect occurs when a substance, usually a metal, absorbs enough light to cause electrons to be expelled from its surface. This phenomenon made a fundamental contribution to the advancement of contemporary physics and offered vital data in support of the quantum theory of light. 

Scientific Principles:

Photon Concept:

• Light consists of particles called photons, each carrying a discrete amount of energy determined by its frequency (E=hv), where "h" is Planck's constant and "v" is the frequency of the light.

Energy Threshold:

• For electrons to be ejected from a material, the energy of the incident photons must exceed a certain minimum value known as the work function (ϕ) of the material.

Electron Emission:

• When a photon hits the material, its energy is transferred to an electron. If the energy is greater than the work function, the electron is emitted from the surface with kinetic energy given by Ek=hv−ϕ.

Intensity Independence:

• The number of ejected electrons depends on the intensity of the light, but the energy of the ejected electrons depends only on the frequency of the incident light.

Historical Development

Heinrich Hertz (1887):

    While researching electromagnetic waves, the photoelectric effect was discovered. Hertz noted that sparks may jump across metal electrodes more readily in the presence of UV light, but he did not investigate the underlying mechanism.

Wilhelm Hallwachs (1888):

    It was discovered that a negatively charged zinc plate would lose its charge when light fell on it, offering preliminary proof for the photoelectric effect.

J.J Thomson (1899):

    Photoelectrically released electrons' charge-to-mass ratio was measured, and it was determined that these particles were identical to those seen in cathode rays.

Albert Einstein (1905):

    Used the quantum theory to provide a theoretical justification for the photoelectric effect. According to Einstein's theory, the energy of the quanta—later referred to as photons—in light is proportional to the frequency of the light. He was awarded the 1921 Nobel Prize in Physics for this achievement.

Robert Millikan (1916):

    Millikan's work, which involved precise tests to validate Einstein's theory, cleared the air for the linear relationship between the frequency of incident light and the kinetic energy of released electrons. Millikan was first sceptical of the hypothesis.

Impacts:

Quantum Theory of Light

    The photoelectric effect provided evidence in favour of the fundamental tenet of quantum mechanics—that light possesses both wave and particle characteristics.

Useful Applications:

   Numerous technologies, such as photovoltaic cells (solar panels), photomultiplier tubes, and photoelectron spectroscopy, rely on the principles underlying the photoelectric effect.

   One of the key ideas in comprehending how light and matter interact, bridging the gap between classical and quantum physics, is the photoelectric effect. 

Particle Nature of light: Einstein's Explanation.

 Particle Nature of light: Einstein's Explanation.

Einstein extended Planck's quantum concept to explain the photoelectric effect in 1905. According to Einstein, the energy in light is not spread out over wavefronts but is concentrated in small packets or energy quanta. Therefore, light (or any other electromagnetic waves) of frequency v from any source can be considered as a stream of quanta and the energy of each light quantum is given by E=hv.
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He also proposed that a quantum of light has linear momentum and the magnitude of that linear momentum is p=h/c. The individual light quantum of definite energy and momentum can be associated with a particle. can behave as a particle and this is called photon. Therefore, photon is nothing but particle manifestation of light.

Light is made up of particles called Photons.

Characteristics of photons:

According to particle nature of light, photons are the basic constituents of any radiation and possess the following characteristic properties:

i) The photons of light of frequency v and wavelength & will have energy, given by E=hv= hc/λ

ii) The energy of a photon is determined by the frequency of the radiation and not by its intensity and the intensity has no relation with the energy of the individual photons in the beam.

iii) The photons travel with the speed of light and its momentum is given by hhv P=h/λ =hv/c

iv) Since photons are electrically neutral, they are unaffected by electric and magnetic fields.

v) When a photon interacts with matter (photon-electron collision), the total energy, total linear momentum and angular momentum are conserved. Since photon may be absorbed or a new photon may be produced in such interactions, the number of photons may not be conserved.... 

“Matter is Energy… Energy is Light…We are all Light Beings” —Albert Einstein.

  

The Short Story Of Atomic Bomb with Oppenheimer. { Manhattan Project }

 💣  Scientist of the Manhattan Project complete the Atomic Bomb destined to end World War - II :     

In the Movie Oppenheimer shows the Atomic Bomb Explosion.
 ( By Director "Christopher Nolan" ).   

💣  During World War the United States used an unprecedented $2 billion to feed an ultra-secret research and development program, the outcome of which would alter the relationships of nations forever Known as the Manhattan Project, it was the search by the United States and her closest allies to create a practical atomic bomb: a single device capable of mass destruction, the threat of which alone could be powerful enough to end the war.   

" Trinity Test " Atomic Bomb explosion effect.

  

💣  The motivation was simple. Scientists escaping the Nazi regime had revealed that research in Germany had confirmed the theoretical viability of atomic bombs in 1939, in support of their fears that the Nazis might now be developing such a weapon, Albert Einstein and others wrote to President Franklin D. Roosevelt (FDR) warning of the need for atomic research By 1941 FDR had authorized formal, coordinated scientific research into such a device. Among those whose efforts would ultimately unleash the power of the atom was Robert Oppenheimer (1904-1967), who was appointed the project's scientific director in 1942. Under his direction the famous laboratories at Los Alamos would be constructed and the scientific team assembled.  

Albert Einstein And Robert Oppenheimer ( 1947).

Robert Oppenheimer in Manhattan Project {Theoretical Physicist}.

💣  An atomic bomb initiates a nuclear chain reaction, thereby releasing truly vast amounts of energy. An initial problem was the production of enough "enriched" uranium to sustain such a reaction Instrumental in the solution was Italian physicist " Enrico Fermi "in a former squash court under Chicago University, he and other scientists created the first ever controlled, self-sustaining nuclear chain reaction. The project ultimately created the first, man-made nuclear explosion, which Oppenheimer called " Trinity ", at Alamagordo, New Mexico, on July 16, 1945...  

      

Mushroom like Structure of the Atomic Bomb Blast, Trinity Test, Alamagordo, New Mexico,on July 16, 1945{ Manhattan Project } By Oppenheimer.   

 💥  " The Atomic Bomb Made The Prospect Of Future War Unendurable. It Had Led Us Up Those Last Few Steps To The Mountain Pass; And Beyond There Is A Different Country. "

                                      ———— J. Robert Oppenheimer. ———— 💣       

History of the United States of America.

🇺🇸   The first residents of  what is  today the United States of America immigrated from Asia about 15,000 years ago by crossing Beringia into Alaska. The colonial history of the US began with the subsequent arrival of settlers from Europe.  

17-th Century Map of America.

🇺🇸   The Thirteen British Colonies that would became the original US states, were founded along the east coast beginning in 1607, and grew very rapidly thereafter. By the 1750s, they had achieved a very high standard of living. Men owned their own farms and could vote in elections for the colonial legislatures.

George Washington {1-st President of US}.

🇺🇸   However, the colonists did not have representation in the ruling British government and believed they were being denied their their constitutional rights as Englishmen. 

The First Design of US Flag { Grand Union Flag, 1776 }.

🇺🇸   The Thirteen Colonies began a rebellion against British rule in 1775. Each of the colonies ousted all royal officials and set up their own governments, which were coordinated out of Philadelphia by Continental Congress. 

Declaration of Independence by Founding Fathers of America (1776).

🇺🇸   In January 1776, a man by the name of  Thomas Paine wrote Pamphlet entitled “ Common Sense ”, in which he outlined the reasons that he felt it was time for the colonies to part company with Great Britain, and form their own independent nation. 

Thomas Paine { Author of Common Sense }.

🇺🇸   The Second Continental Congress charged Thomas Jefferson with the responsibility of writing a declaration of independence that would be sent to Great Britain.  

Thomas Jefferson (3-rd President of US).

🇺🇸   On July 4, 1776 this declaration was officially adopted by the Continental Congress. With the ratification of the Articles of Confederation and Perpetual Union, the United States of America became a nation state in 1781. These articles stated that each colony was to act as an independent state, and that each had the right to pass laws within their territories.  

American Civil War between the Union and Confederacy { 1861 - 1865 }.

 

🇺🇸   Only two people, John Hancock and Charles Thomson signed the declaration of Independence on July 4 1776.

Right side - John Hancock ; Left side - Charles Thomson. 

🇺🇸   This new nation was to be headed by a president, rather than a monarch. This President would be elected by the Legislature, which was in turn elected by the people. This type of government is known as a republic....

" America Will Never Be Destroyed From The Outside. If We Falter And Lose Our Freedoms, It Will Be Because We Destroyed Ourselves. 🇺🇸 "

                                  — Abraham Lincoln 🇺🇸 (1809 - 1865)  

Albert Einstein ( German—born Theoretical physicist )

Albert Einstein was regarded as the founder of modern physics, Albert Einstein was born to Hermann Einstein,a salesman and an engineer,and Pauline Kochon on 14 March 1879, in Ulm, Kingdom of Württemberg, German Empire. He received his education at the Luitpold Gymnasium in Munich. His grades in physics and mathematics were always excellent. He completed his schooling at the Argovian Cantonal School, Aarau, Switzerland, and at the age of seventeen he joined the Zürich Polytechnic for a physics and mathematics teaching diploma programme.

Einstein received his degree in 1900 but failed to get a suitable teaching job. With his friend's help, he joined the Federal Office for Intellectual Property as an assistant examiner – level lll .

Einstein secured a permanent position at the Swiss Patent Office in 1903. His conclusions about the space-time connection and the nature of light were aided by his work and experiments during this job.

Einstein completed his Ph.D. from the University of Zürich in 1905 and published four papers in the scientific journal named ″ Annalen der Physik ". The year was miraculous for him as these papers on photoelectric effect, Brownian motion, special relativity, and mass-energy equivalence ( E= mc² ) were significant contributors to the foundation of modern physics. They reformed the views on time ,  space, and matter. In the next few years, Einstein came to be recognized as a major scientist.

In 1908 he joined the University of Bern as a lecturer and the next year he was appointed as an associate professor at the University of Zürich. Two years later, in 1911, he was appointed as a professor at the Charles-Ferdinand University, Prague. Here he wrote several scientific works. Einstein returned to Zürich the next year, and for the two years that followed, he joined ETH Zurich as a professor of theoretical physics.

Einstein was appointed as the director of Kaiser Wilhelm Institute of Physics in the year 1914 and as the president of the German Physical Society in 1916. He developed the general theory of relativity between 1907 and 1915. It was published in 1915. In 1916, Einstein published " Relativity: The Special and the General Theory " in German. Its first English translation was published in 1920. Divided into three parts, the special theory of relativity, the general theory of relativity, and the consideration on the universe as a whole. It is considered a groundbreaking scientific work.

In 1921, Einstein was awarded the Nobel prize in physics " for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect. " 

 In the year that followed, he travelled extensively. In 1933, he joined the Institute for Advanced Study in the United States, and by 1940 he became an American citizen.

Einstein published numerous scientific and non-scientific works. Some of his published works include: Sidelights on Relativity (1922), Cosmic Religion: With Other Opinions and Aphorisms (1931), Essays in Science (1934), The World as I see It (1949), Out of My Later Years (1950), and Ideas and Opinions (1954). 

Einstein died on 18 April 1955, aged seventy-six, in Princeton, New Jersey.