Modern Physics

Basically, there are two types of Physics, Modern Physics and Classical Physics. Modern Physics believes in dual nature both particle and wave nature of matter. It provides a microscopic vision of matter, It is based upon Planck’s quantum theory of light and De Broglie’s idea of matter-wave. Atomic Physics, Nuclear Physics, Relativistic Physics, and Quantum Physics are examples of modern Physics.
What is Modern Physics?
Modern Physics designates the new conceptions of Physics developed during the first three decades of the 20th century, which resulted from the theoretical propositions of physicists Einstein and Max Planck. After the emergence of relativity of Einstein and the quantization of the electromagnetic waves , this new field of study has emerged, expanding the limited horizons of classical physics.
Broader than the Physics Classical, to modern physics is able to explain phenomena of scales very small  and extremely high speeds, very close to the Speed of light. 20th century physicists realized that current knowledge was not enough to explain phenomena such as the photoelectric effect or blackbody radiation. Thus, several hypotheses began to be raised about the nature of light and matter and about the interaction between them.
Important Discoveries in Modern Physics
Several experiments marked the history and development of Modern Physics. Among them, we can mention those who provided us with a deeper understanding of the structure of matter and atoms and also about the nature of light. check out some examples of these important discoveries that marked the beginning of Modern Physics:

  • In 1895, Wilhem Röntgen discovered the existence of X-rays, an invisible type of extremely penetrating radiation.
  • In 1896, Antoine Becquerel discovered the existence of
  • A few years later, in 1900, the German physicist Max Planck proposed that the energy charged by the electromagnetic field had quantized values , integer multiples of a minimum and constant amount.
  • In 1905, through his theory of relativity, Albert Einstein showed that references that move at very high speeds, close to the speed of light propagation , experience the passage of time and the measurement of distances in different ways.
  • In 1913, Niels Bohr proposed that the energy levels of electrons scattered around atomic nuclei are quantized, that is, their energy is given by an integer multiple of a minimum value.
  • In 1924, the wave- particle duality , established by physicist Louis De’Broglie, showed that any body can behave like a wave.
  • In 1926, Quantum Mechanics appeared , the result of the work of physicists like Werner Heisenberg and Erwin Schröedinger.

In other words, Modern Physics was able to explore the nature of the microscopic world and the great relativistic speeds , providing valuable explanations for various physical phenomena that were, until then, misunderstood.
Milestones of Modern Physics
→ Atomistic theory
The atomistic theory originated among Greek thinkers like Tales of Miletus and the atomists Democritus and Leucipo. For these thinkers, matter was made up of smaller, indestructible and indivisible particles, which were called atoms.
Atomistic theory gained strength thanks to the different atomic models proposed throughout physical studies. Below are some important scientists and their atomic theories:

  • John Dalton:believed that atoms were massive and indivisible and that substances were formed by atomic combinations of different proportions.
  • JJ Thomson:according to this scientist, electrons, which have a negative electric charge, were scattered on the surface of a positive charge.
  • Ernest Rutherford:for Rutherford, atoms had a positive electrical charge concentrated in an extremely dense and reduced region, called the atomic nucleus.
  • Niels Bohr: according to Bohr’s model, electrons were located around atomic nuclei with quantized energy, that is, they occupied only specific levels of energy, which were multiples of a smaller amount.

The current conception of what atoms are has had several contributions throughout history, going through several changes. Some of the most important proposals for our understanding of atoms and matter came from physicists like De’Broglie, Heisenberg and Schröedinger.

  • Louis De’Broglie: proposed the existence of matter waves, a property that explains the dual behavior of electrons.
  • Werner Heinsenberg: proposed the uncertainty principle, indicating that it would not be possible to determine, simultaneously and with total precision, the position and the quantity of movements of the quantum particles.
  • Erwin Schröedinger: through his equation, he was able to determine the most likely regions to find an electron around the atomic nucleus.

→ Blackbody radiation
For physics, it is classified as body black any body able to absorb all incident radiation on it, reissuing it in the form of thermal radiation according to their temperature.
The problem with blackbody radiation was one of the main open questions in physics in the early 20th century. Using the hypothesis of quantizing the energy of electromagnetic waves emitted by black bodies, the German physicist Max Planck presented the solution to this problem.
→ Oil drop experiment
The oil drop experiment, carried out by physicist Robert Andrews Millikan, was able to determine the order of magnitude of the electron charge . The apparatus used in this experiment consisted of a spray bottle, which splashed oil droplets between two plates electrically charged in the vertical direction, so that the droplets remained static in the air. Until the realization of this experiment, the charge of electrons was not known, only the ratio between its charge and its mass .
→ Franck-Hertz experiment
The experiment of Franck-Hertz validated the atomic model proposed by Niels Bohr. This experiment showed that it is only possible to excite the atoms of a gas from specific energy levels , as well as predicting the quantization of energy levels, proposed by Bohr.
→ Rutherford experiment
Rutherford’s famous experiment was actually carried out by two of his students, Hans Geiger and Ernest Mardsen.In this experiment, a thin sheet of gold was bombarded by alpha particles at high speed. It was noticed that, after the collision, the angles of some of these particles varied a lot. In addition, in some cases, alpha particles were ricocheted , which suggested the existence of heavy and extremely dense atomic nuclei.
→ Discovery of gravitational lenses
The phenomenon of the gravitational lens occurs due to the distortion of space-time exerted by large masses, such as those of stars and planets. According to general relativity, proposed by Albert Einstein , the gravity exerted by massive bodies is the result of deformation in the space-time relief. As a result, when propagating through the deformed space-time, the light would suffer a deviation.
This phenomenon was observed by astronomers by measuring the duration of the total solar eclipse in 1919. The measurements were made simultaneously in the city of Sobral , located in the state of Ceará, and in São Tomé and Príncipe .
→ Michelson-Morley experiment
The Michelson-Morley experiment proved that electromagnetic waves are capable of propagating in the vacuum itself, so they do not need a means for this. To prove this property, researchers Albert Michelson and Edward Morley used a large interferometer  immersed in a pool filled with mercury.In this way, vibrations of any kind, capable of affecting the extremely sensitive measure, would be avoided.
In the experiment in question, the time for the light to be reflected by precisely aligned mirrors was measured. If the Earth moves in the medium in which the light spreads, small deviations in the reflected beams should be observed, which did not happen. Thus, the researchers proved the proposed theory.
→ Photoelectric effect
The photoelectric effect was a phenomenon without a satisfactory explanation until the studies developed by Albert Einstein.For explaining this effect, Einstein was awarded a Nobel Prize in Physics. Through Max Planck ‘s idea , Albert Einstein expanded the energy quantization theory of blackbody radiation to any type of radiation, thus establishing the notion of wave-particle duality.
General relativity
The relativity general is a generalization of the special theory of relativity, also developed by German physicist Albert Einstein. According to this theory, massive bodies, like planets and stars, are capable of deforming the weave, or the relief, of space-time. This deformation, in turn, gives rise to gravity.
Important Topics and Applications of M.Physics are given below:

External sources 
https://en.wikipedia.org/wiki/Modern_physics

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