Electrons - Particle or Wave?

                 Since ancient times we are wondering what is matter made up of? Democritus said matter is made of indivisible particles and named them Atomos. Maharshi Kanad also named it Anu. Then Dalton came he predicted atoms then J J Thomson gave atomic model by experimenting using cathode rays he said atom is made of negatively charged electrons suspended in positively charged medium and gave analogy of plum pudding or watermelon.

                 Einstein proved existence of molecules (group of atoms) but still actual model of atom was unknown to the world then great mind Rutherford came and he performed his famous experiment called Rutherford scattering experiment. And he concluded the atom is made of positively charged nucleus and negatively charged electrons revolving around the nucleus in circular orbits like sun-earth system. And showed that maximum space in atom is empty space. But the problem was in circular motion electron has tangential acceleration. From Maxwell's Electromagnetic theory we knew that accelerating charged particle emit electromagnetic radiation. If that's true then electron should emit electromagnetic radiation due to which its energy will decrease which kept it in circular orbit and it will spiral down into nucleus and bammmm... they will neutralize each other which says that atom should not exist at all because of this instability. 

                 So to resolve this idea Neil's Bohr came who is one of the founders of quantum mechanics he said that electrons revolve in some special orbits so that the are not accelerated and don't emit electromagnetic radiation. But if the transition of electron occurs from one orbit or another corresponding amount of energy is released or absorbed depending on transition. 

                So from previous discussion we knew that light has dual nature particle as well wavy one. After some efforts and experiments we came to know that electrons themselves behave as waves and particles. If they are travelling they show wavy nature if the are interacting they show particle nature. Not just electron but also all the subatomic micro macro particles as well classical bodies show wave nature.

       

                 Just the difference is wave nature of particle in subatomic and micro world is much more significant than the classical real macro world because wavelength (distance between crest and trough) of that wave nature depends inversely on mass of object. As the subatomic particles are very small and very light because of this relation its wavelength become more significant as its size. But for heavy bodies because of their huge mass wavelength of associated wave is smaller than atoms themselves so we don't care about it in daily lives. This relation of associated wave nature was give by De-Broglie called as De-Broglie Hypothesis. Experiments were done and wave nature of subatomic particles were confirmed. Famous experiment was  Davisson-Germer experiment. Most important thing about this wave is that its not an actual wave but its probabilistic wave. This wave its peaks and valleys which tells how much its likely to find that particle at that position. We will see that later how probabilistic waves determine about its state.

Actual orbit of electron in atom look like this.

                But the main conclusion from this discussion was matter also behave as wave so it is called as Matter Waves. It has dual nature wavelike and particle like.

                So up till now we know that Waves behave as particles and particles behave as waves so this phenomena called as Dual Nature of Matter and Radiation. If its travelling or in motion and we are not looking at it, it behave as wave but if its interacting and we are looking at that event occurring it will show particle nature.

Light -Wave or Particle?

                 In daily life we see two different objects that is particles and waves. But when we will look at actual nature of particles and waves we won’t be able to distinguish both wave behaves as particles and particle behaving as waves.

                 At least from elementary science you know that light is nothing but an electromagnetic wave that is mutual and combined alternating electric and magnetic field inducing each other and sustaining that mutual togetherness forever. We all know speed of light is constant of nature.

                But at the dawn of physics when we didn’t know nature of light,  Newton thought that light is made up of particles which strike our skin so that we feel warm but at the same time he was successful to demonstrate splitting of white light into different colors. He named those particles corpuscles. So we got confused is it a wave or particle? But in later days we came to know that light is nothing but waves like water waves. After some years we came to know that flowing current through wire induce magnetic field around them and motion of conductor in magnetic field like field of magnet produces current in conductor. So Michael faraday knew there must be relationship between electric and magnetic field but he couldn't prove that because of very abstract mathematics but later his student James Clerk Maxwell showed that there's is indeed a strong relationship between those two. They are not separate phenomena but the different sides of same coin. So he unified those two it into single phenomena called Electromagnetism. And he also showed that electromagnetic field has same speed as the light as it was discovered before so light is indeed an electromagnetic radiation. But the problem was as per our normal intuition we know that  any wave requires a medium like water waves require water , sound waves require air. So scientist said there is an medium called ether we can't see it, can't feel it but its there in all space around us our earth moves through it like a ball will move through water. So it is possible to test an existence of an ether by finding relative velocity between earth and ether when earth moves through it. Relative velocity is velocity/speed of one object with other. Experiments were done but no ether was found. So it was mystery through which medium electromagnetic radiation propagate? But at least it was concluded that light is a wave. Experiments also showed that light shows properties of wave like interfering with each other making beautiful color patterns on wings of butterfly, diffracting from curved surface like we can see shadows of light on a ball, polarization like we use spectacles which protect us from ultraviolet radiation. But it was not enough some of the properties it couldn't explain like blackbody radiation (heat radiations emitted when a body is heated), photoelectric effect (when light fall on some metal electric current flows through it).

                To explain blackbody radiation most successful theory was given by Max Plank. He said light is not emitted continuously like stream or flow by the heated body but emitted in installments like packets or groups of energy. He called those packets of energy as Quanta. But the medium for light wave was still  mystery but then genius of Einstein came into picture from his Special Theory of Relativity he showed that light is indeed consist of stream particles called Photons. He proved successfully the results of photoelectric effect. And not just that, he also showed that ether was not found because it doesn't exist at all. 

                So From this discussion we know that light behave like a wave (electromagnetic radiation) when it travels through space but it behaves as particles when interact with matter. So light has dual nature.