Light….a very strange and one of the most important elements in the universe. for a long time people were confused about its nature i.e. whether its a particle or a wave. So, two theories were formulated. One is particle theory and other is wave theory. Particle theory describes that light travels for the movement of a special particle which we called Photon. Whereas, wave theory tell us that light travels in the form of wave. However, Quantum Mechanics shows us that none of these theories are completely correct. Now due to advanced research and modern technologies we able find that light has both the property of wave and particle. Even Albert Einstein also believed that light is a particle (photon) and flow of photon is a wave. If someone will ask my personal opinion, then my answer is same as Einstein. And in reality, it is true. Today scientists named this as Wave-Particle Duality of light

                       But the scientist have not discovered this amazing fact in a single day. It had taken very long time and many small and basic steps. One such step is Double-Slit Experiment. It basically help us to understand the wave property of  light. 
Young’s experiment, often referred to as double-slit experiment. It was used at the beginning of the 19th century to prove that light exhibits wave properties. This exploits two specific properties of waves:-

1.If a wave reaches a small opening. It bends. This phenomenon is called diffraction. The size of the opening has to be comparable to the wave’s wavelength  for diffraction to occur.

This is the diffraction of a single slit obtained on a screen
This is the diffraction of a single slit obtained on a screen 

2. When two wave encounters, they do not collide but strengthen or weaken each other depending on what the height or displacement of both waves is. Phenomenon is called interference. For example, when two waves of opposite displacements encounter, they cancel and weaken each other. This type of interference is called destructive interference.When waves of same displacement encounters, they strengthen each other. This is called constructive interference

                In this experiment, two slits which are very close to each other, are used. Light passes through both slits and spreads to the medium behind the opening. Due small distance between the slits and light waves which passed through both slits meets together. If we situate a plates detecting the position of individual beams of light strikes it, a specific pattern created which we called as interference-pattern. It consist of dark and light strips. Light strips occurred where constructive interference happened and dark strips occurred where destructive interference happened. Since, we can detect the signs of interference so we can now say that light also exhibit wave property.

Double slit experiment
Double Slit Experiment 

             Yeah, it’s right that this experiment is very simple but we should not forget that complex elements of universe always evolve from simpler ones. This experiment shows the light towards the development of the wave theory, which helped us a lot to understand this magnificent universe.

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                                                                     -Ratnadeep Das Choudhury
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