Breaking Barriers - The Tunnel Effect

The world of quantum physics is an amazing place where particles can do weird and wonderful things. Small subatomic particles are able to pass through barriers, this is because of the tunnel effect.
Ishan Arvikar
Grade 6



  1. Can only atoms pass through barriers? If atoms can possibly pass through barriers why can't we?
  2. What are atoms?
  3. what makes up the nucleus?
  4. Is light a wave or particle?





Everything around us is composed or made up of very small things known as subatomic particles. When scientists discovered more about these particles they realized that classical laws of physics did not apply in a tiny world. A new theory was developed which we know as Quantum physics. The world of quantum physics is an amazing place where particles can do weird and wonderful things, acting totally unlike the objects that we experience in day-to-day life.

These small subatomic particles can pass through barriers, this is because of the tunnel effect. Matter is anything that occupies space and has mass. All physical objects are composed of matter and can be easily observed through their state. The three states of matter are solid, liquid and gas. 

Relationship between States of Matter-

Heating and cooling, a substance may change one state to another i.e. Solid to Liquid, Liquid to Gas, or Solids to Gases. When a material changes state, its smallest units, called molecules, behave differently. However, the material's molecules do not break apart and form into a different material. They remain the same. A change of state is a reversible change. 

Matter is made from molecules, which can be separated relatively easily. Molecules are made up of atoms and are joined by chemical bonds that are more difficult to break. Particles that are smaller than the atom are called subatomic particles. The three main subatomic particles that form an atom are Protons, Neutrons, and Electrons. The center of the atom is called the nucleus. Everything around us – plants, trees, houses, food, light, air, water, and even human beings consist of “Subatomic Particle”.

People tried to understand the world from their experience, what they can feel, see and observe. Scientists started to discover the world. By the end of the 19th-century Scientists such as Sir Issac Newton explained the “Law of Universal Gravitation”-why things fall on the ground, why planets orbit around the sun, and why the Moon revolves around the earth. He also explained – three laws of Motion. These laws are part of Classical Physics. When scientists started to discover more, they realized that law of physics did not apply in the tiny world of Subatomic particles.

Mystery of LightWave or Particle

There was a discussion during Newton’s time regarding light. The debate was about if light was made of particles or waves. As per Newton, light was formed by tiny particles that only moved in one line. He called these particles as corpuscles. Others believed that light was made of waves as light would not be able to change direction when diffracted. Thinking of light as a wave and particles allows us to explain the following Light phenomena.

Reflection is when light bounces off an object. If the surface is smooth and shiny, like glass, water, or polished metal, the light will reflect at the same angle as it hit the surface. 

Diffraction refers to various phenomena that occur when a wave encounters an obstacle or opening. It is defined as the bending of waves around the corners of an obstacle

Refraction is the phenomenon that occurs when light changes direction while passing from one medium to another or from a gradual change in the medium.

This very unusual behavior of light is called the wave-particle duality. This strange behavior of light did not comply with the classical laws of Physics. That is how Quantum theory started.

In the late 19th century James Clerk Maxwell suggested that the behavior of light is described as waves of electricity and magnetism: in other words, electromagnetic waves.  The wave is a movement that results from a disturbance that transports energy but not matter. The energy is moved through space with rising and falling movements that may be powerful or less.

Light moves at an incredible speed. Light travels at a speed of 300,000 km per second. At this speed, it would be possible to go around the world seven times in just one second! This is how Maxwell got around the old “wave or particle” conflict, and he decided in favor of the notion of light behaving as a wave. 


Atoms are formed with negatively charged particles which are called electrons. An electric current is the movement of electrons within matter.  

If we make an electric circuit using a light bulb and two pieces of metal, and then light up the metal with VIOLET light, we will see that the bulb also lights up.  This happens because the electrons jump from one piece of metal to the other, and this allows the electric current to circulate.  But if we do the same with RED light, we find that the electrons do NOT jump and the electric current does not circulate, and naturally enough, the bulb does not light up. Using Planck’s ideas about quanta, Albert EINSTEIN realized that if light, rather than being formed by waves, consisting of particles (which he called PHOTONS), it would be possible to explain the photoelectric effect in the following way.  If we light up the metal with VIOLET light, the VIOLET PHOTONS collide with the electrons of the metal and knock them out one by one. RED PHOTONS, on the other hand, do not have enough energy to knock the electrons from the metal, and no matter how many photons we send, they will not be able to do it. 

Today, we use this photoelectric effect in many devices for a variety of uses. One example is the sensors in the automatic doors of elevators or stores. It is also used to create electricity in solar panels. 


Einstein liked to call Photons as LIGHT QUANTA, or ENERGY QUANTA. These photos are special particles because they carry no mass, are invisible, and travel at the SPEED OF LIGHT. 


The color of light is determined by its FREQUENCY- the number of waves that pass a given point per second. Depending on the color of the light, we will have one type of photon or another. We can have blue, green, yellow, red photons, etc. The higher the frequency of a photon the more energy it will have. The frequency of blue light is greater than the frequency of red light and therefore BLUE photons will have more energy than RED photons.  BLUE photos are more energetic than RED photons. Humans can only see a small part of the frequencies of light. Ultraviolet (beyond violet) light and infrared (below red) light mark the limits of the colors that our eyes can see. 


According to maxwell-Thinking of light as a wave allows us to explain phenomena such as diffraction and according to Einstien other phenomena of light can only be explained if we think that light is formed by particles. Finally, some phenomena can be explained using both theories, for example how light travels in a straight line (reflection and refraction). 

We must accept the fact that light sometimes behaves like a Wave while at other times it behaves like a particle. What causes it to behave one way or another? Well, this actually depends on how we are observing things. In other words, it depends on the type of experiment that we are carrying out.  This very unusual behavior of light is called the WAVE-PARTICLE DUALITY. But the most incredible thing is that light particles aren't the only ones to behave like this, other particles also show wave-particle duality. 

The strange behavior of light did not fit in with the old laws of Physics. That is how Quantum Theory started. 

The Atom - 

Back in ancient, about 2,500 years ago, people wondered what matter was made of. Some philosophers thought that it was possible to keep putting things into smaller pieces for as long as we licked. There were others, such as Democritus, who thought that there came a moment when the matter could not be divided any further. In other words, that it was formed by invisible particles, which they called ATOMS (in Greek, “atom” means “invisible,” or: which cannot be divided.”)

An Atom is the smallest part of an element that can be broken down and still have the characteristics of that element. The parts of an atom are protons, electrons, and neutrons. A proton is positively charged and is located in the center or nucleus of the atom. Electrons are negatively charged and are located in rings or orbits spinning around the nucleus. The number of protons and electrons is always equal. This equality is important so that the atom is neither positively nor negatively charged. It is said to be neutral. The third part of the atom is the neutron. Neutrons are neither positive nor negative and are located in the center of the nucleus of an atom along with the protons. Protons and neutrons are the heavy parts of an atom. Their combined weights are called the atomic weight of an element. Electrons are so light that we say they do not have weight. Structure of an atom: The atom makes up of 3 particles protons, electrons, and neutrons. In the middle, we have a nucleus that consists of protons and neutrons the neutron is positively charged while the and the neutrons have no specific charge. On the outside, we have our electrons.

The Tunnel effect:

Quantum tunneling is the phenomenon where particles can penetrate a potential barrier. However, this effect depends on its barrier and the number of atoms. For this to work our atoms would need a potential barrier thin enough for the wave to pass through. This also means that not all atoms are guaranteed to go through.

The quantum tunneling effect is a quantum phenomenon that occurs when particles move through a barrier that, according to the theories of classical physics, should be impossible to move through. The barrier may be a physically impassable medium, such as an insulator or a vacuum, or a region of high potential energy.

In classical mechanics, when a particle has insufficient energy, it would not be able to overcome a potential barrier. In the quantum world, however, particles can often behave like waves. On encountering a barrier, a quantum wave will not end abruptly; rather, its amplitude will decrease exponentially. This drop-in amplitude corresponds to a drop in the probability of finding a particle further into the barrier. If the barrier is thin enough, then the amplitude may be non-zero on the other side. This would imply that there is a finite probability that some of the particles will tunnel through the barrier.

Here is a list of a few things that depend upon Quantum Physics in our Daily Life:

1. Toasters: The heating element of the toaster glows red to toast a slice of bread. The rod in the toaster gets hot, which, in turn, is responsible for toasting the bread.

2. Fluorescent light:  In fluorescent lighting, a small amount of mercury vapor is excited into the plasma. Mercury has the ability to emit light in the visible range.

3. Computer & Mobile Phone: The whole computer world is based on the principle of Quantum Physics. Quantum Physics talks about the wave nature of electrons, and, so, this forms the basis of the band structure of solid objects on which semiconductor-based electronics are built.

4. Transistor: Transistors have widespread uses and are used to amplify or switch electrical signals and electrical power.  Computer chips are the source of all the technological gadgets which have become central to human existence. 

5. Magnetic Resonance Imaging: The study of soft tissues can easily be carried out with the use of MRI. Thanks to Quantum Physics that the diagnosis and treatment of some life-threatening ailments have been possible.

6. Telecommunication: Fiber optic telecommunication is possible only because of lasers. Communication has been made extremely easy because of the important role of Quantum Physics.

7. Laser: The working of lasers involves spontaneous emission, thermal emission, and fluorescence. An electron, when excited, will jump to a high-energy level. However, it will not stay in the high-energy level for a long time, and jump back to the lower energy state which is more stable; and, thereby, emit light. 




Quantum Physics, this theory is still being tested by so many scientists. Turns out my hypothesis was correct because if we ever had a scenario where this was happening (obviously we can't see it)we would never truly know whether our atom got to its destination. Though it may go through the potential barrier we still don't have an estimate on how many times these atoms will pass. The Discoveries that scientists have made in Physics have been applied to many inventions. Our house can be full of the Gadgets, we can also call them as Quantum gadgets. For example-Microwave, Mobile phones, X-ray machines, Lasers, induction Cooktop etc. Everyday science brings us closer to a part of nature that had been unknown to us human beings. A scientists move ahead with their inventions and discoveries we will be able to do incredible things.


Britannica, The Editors of Encyclopaedia. "Matter". Encyclopedia Britannica, 25 Feb. 2021, Accessed 17 March 2021

Peerson, T. (2019, September 10). What is an atom. What is an atom. Retrieved March 17, 2021, from

Sundermier, A. (2016, September 23). 99.9999999% of your body is empty. Retrieved March 17, 2021, from 

Britannica, The Editors of Encyclopaedia. "Pauli exclusion principle". Encyclopedia Britannica, 19 Jan. 2018, Accessed 17 March 2021.

Bairad, C. (2016, April 16). Do atoms touch each other. Do atoms ever actually touch each other? Retrieved March 17, 2021, from

Britannica, T. Editors of Encyclopaedia (2017, May 19). Boson. Encyclopedia Britannica.  

Britannica, T. Editors of Encyclopaedia (2019, March 20). Quantum. Encyclopedia Britannica.

Britannica, T. Editors of Encyclopaedia (2017, June 16). Quantum field theory. Encyclopedia Britannica.


Youtube videos - Jacob Sherson Dr. Shohini Ghose


I would like to thank my teachers and parents for supporting me and helping me with this project.

I would like to thank Maryam Tsegaye for giving me an idea about this project (Khan academy winner for her detailed video on Quantum Physics).