# Modern Physics

Physics is a prominent field of science that is filled with a number of remarkable and astonishing experiments, facts and discoveries which have been life-changing contributions. Modern Physics is a subfield of Physics and consists of a variety of ground-breaking inventions and concepts. Dealing with post-Newtonian concepts, Modern Physics is based on two major milestones of the 20th century, i.e. Relativity and Quantum Mechanics. Oftentimes students preparing for class 12th boards or competitive exams like JEE Mains, JEE Advanced etc have to cover this topic. Here is a blog that aims to elucidate important topics, formulas and concepts of modern physics.

## Modern Physics: Topics

Being a vital part of the physics syllabus for Class 12, modern physics consists of a variety of foundational topics and some of these have been mentioned below:

• Atomic Theory and the Evolution of the Atomic Model in General
• Michelson- Morley Experiment
• Geiger-Marsden Experiment (Rutherford’s Experiment)
• Quantum Thermodynamics
• Photoelectric Effect
• Wave-Particle Duality
• Perihelion Precession of Mercury
• Solid
• Stern-Gerlach Experiment
• Frank-Hertz Experiment
• Gravitational Lensing

Check Out: Class 12th Physics Electrostatics Notes

## Modern Physics: Formula

In order to cover different topics of modern physics, it is important to go through the formulas which you must remember as they will help you solve numerical problems in competitive exams. There are different formulas required to crack derivations and concept based questions. Here are the major formulas of Modern Physics that you must know about:

You might be interested in: Physics Syllabus for Class 12

## Modern Physics: Notes

While gearing up for engineering entrance exams or any other rigorous competitive exams, you must learn about the basic core concepts of modern physics. Making notes while practising a subject will also help you in the last moment revision. Mentioned below are important notes for this topic:

### Effect of Collector’s Potential on Photoelectric Current

• Current for zero value potential reflects that the electrons are ejected from the given surface of the emitter with random energy.
• Due to a change in potential, the electrons gradually changing in the number reflects that the ejected electrons possess a variety of velocities.
• For a negative potential of the collector, the current is reduced to zero indicating that is some upper limit of the energy that electrons emit.
• The stopping potential does not depend on the intensity of the light.
• Current is dependent on the intensity of the incident light.

### Laws of Photoelectric Effect

• Referred to as an instantaneous process, the photoelectric effect is explained as a phenomenon which occurs when electrons are emitted from a metal surface when the light of an adequate frequency is incident upon.
• The photoelectric current is independent of the frequency of light and is directly proportional to the intensity of light.
• The maximum velocity of the electrons (stopping potential) is dependent on the frequency of the incident light.
• Threshold Frequency is the minimum frequency below which the emission of electron stops.

### Bohr’s Atomic Model

• The nucleus which is the central part of the atom contains positive charge and almost the entire mass of the atom. Also, the electrons revolve around the nucleus in a fixed circular orbit.
• Stationery Orbits/Permitted Orbits are the fixed circular paths in which electron revolves without radiating any energy.
• The electrons possess an angular momentum (L=  mvr) while revolving in the stationery which is an integral multiple of h/2𝝿

L= mvr= nh/2𝝿

In the above-mentioned formula, h is Planck’s constant and n is an integer

• While moving, the electron can change their orbits. When they absorb the energy they move into a higher other orbit and the emission of energy takes place whenever an electron moves into a lower orbit. If f is the frequency of radiant energy,

• Radioactivity takes place due to the disintegration of a nucleus
• Law of conservation of charge is also interconnected to the laws of radioactivity.
• External conditions like Temperature, Pressure etc. do not affect the rate of disintegration.
• Each of the product disintegrations is a new element which has chemical and physical properties distinct from that of the parent atom.

Take a look at the Top 10 Toughest Exams in India

## Important Discoveries in Modern Physics

There have been a number of different experiments which have marked the history of Modern Physics. There are several that help in providing a deeper understanding of the structure of matter and atoms. A few examples of these discoveries are:

1. Wilhelm Röntgen in 1895 discovered the existence of X-rays.
2. Max Planck was a German physicist. In the year 1900, he proposed that the energy-charged by the electromagnetic field can be quantified.
3. In 1905, Albert Einstein, through the theory of relativity explained and showed that references move at very high speeds. That speed is close to the speed of light propagation.

Also, checkout 15 Must Read Bestselling Quantum Physics Books 2021

Hopefully, these notes and formulas of modern physics have helped you in getting a stronghold over the concept. Confused about how to make the right career choice after class 12th? Book an online session with our Leverage Edu experts and let us help in making an informed decision to soar towards your dream career!