EVOLUTION OF PHYSICS- THE MODERN INTERPRETATIONS OF PHYSICS (1)

No other discipline of science has grown and developed rapidly as Physics. In the blogs that follow I will try level best to describe the modern notions of this subject, but wait...do you know that the Newton's Law and its numericals, Newton's Universal Law of Gravitation, the Bohr's Model of Atom etc that you learnt hard for your exams do not hold good universally and are 'false statements' according to modern notions and human research.

Then why did we learn all these statements in the first place. This is a very relevant question, we solved questions based on these so called 'false statements' and lost marks for not solving it correctly, when the 'law' itself is wrong!

We learnt them because, we should understand were they went wrong and how they were corrected. For example, earliest understanding of nature was such that the universe was made up of matter, but later we learnt that matter is made up of atoms, Democritus, an ancient Greek philosopher later postulated that atoms are the tinniest particle in the universe which is indivisible, we later learnt that atoms contain in them protons, neutrons and electrons, further understanding of atomic structure revealed the presence of a positively charged nucleus which was confirmed by Rutherford as a result of his ⍺-particle scattering experiment, Bohr later postulated that electrons move around the nucleus in circular paths called 'orbits', but the contributions of many other scientists like, de-Broglie, Heisenberg, Schrödinger, in turn confirmed the presence of 'orbitals', which are present within the orbits...which is now the modern accepted notion of structure of atom. 

Now look...we just witnessed how from the broad concept of matter we reached the minutest corners of an atom. Who knows within a decade or so the new generation might be learning particles within the electrons and protons!

This is just the case of the 'atom', in science I can give numerous other examples which suggests that science is living entity which constantly gets refined from time to time, and will forever be the greatest 'product' of human resource...

Okay then...lets meet some scientists of the modern era...I will try to include all of them in my series of blogs for their passion for science is unparalleled which yielded them great breakthroughs in their of field...

Let us learn about 'atom' today...

Atom is the smallest particle in the universe. All matter is made up of atoms, and it is the basic unit of all objects whether macroscopic or microscopic.

Scientists were keen on understanding the structure of atom and I should say over the years we have a wide variety of structures for the atoms ranging from the Thomson's Model to the modern accepted structure... In this blog we will be dealing with Thomson's and Rutherford's Atomic Model...

PLUM PUDDING MODEL OF AN ATOM

                                                        

Figure 1: Sir J.J Thomson

Sir JJ Thomson was an English Physicist who is often associated with the discovery of the negatively charged particles present within the atom, now called as the 'electrons'. He discovered these electrons when we was doing the 'cathode ray experiment'. The cathode rays itself consisted of electrons which moved from the cathode (negative end) to the anode (the positive end). JJ Thomson won the Nobel Prize in Physics in 1906 for the discovery of electrons. The Thomson's Model of Atom is given below for your reference,

                                               

Figure 2: Plum Pudding Model of an Atom

You can observe that in this model of atom the negatively charged particles which we call the electrons are embedded in a pool or sphere of positive charge. It should be noted that the positive and negative charges are equal in magnitude so that the atom becomes electrically neutral which in turn makes it stable.

But unfortunately, Thomson's Model was discarded as it could not explain the experimental results of many other scientists in particular,'one man', a man who contributed wholeheartedly for the development of atomic structure, a man who will later be called, 'The Father of Nuclear Physics'. 

Yes...you guessed it right!...it's Rutherford...Sir Ernest Rutherford...

RUTHERFORD'S MODEL OF AN ATOM

I should say, his 𝛂-particle scattering experiment, its postulates and his observations still resonate in my mind. And it was a sure question for our 9th grade final exam. I don't know if you believe me or not, I wrote about this experiment as if  I was doing this it myself...and so I love explaining this model than any other model...😊

                                                 

Figure 3: Sir Ernest Rutherford

THE 𝛂-PARTICLE  SCATTERING EXPERIMENT

Rutherford took a gold foil of at least 1000 atoms thick. Now, why gold foil? This is because gold foil was very thin and he needed just that!

The 𝛂-particles had a considerable amount of energy. Directly quoting from my textbook,𝛂-particles are doubly charged helium ions with mass 4u and as and when it moved it had some energy associated with it.

Rutherford is about to do the experiment...perfect silence in his lab...

Rutherford screams with joy!!!

He is really astonished by his observations, this is evident from his following quote...

'' This result was almost as incredible as if you fire a 15-inch shell at a piece of tissue paper and it comes back and hits at you!'' 

                                          

His observations were truly remarkable.

1. He found that most of the alpha particles passed straight through the gold foil without getting deflected.

2. Only some alpha particles were deflected from their original path.

3. Some alpha particles rebounded after getting deflected.

Rutherford in turn concluded that,

1. The positively charged region inside the atom was small.

Explanation: Alpha particles are positively charged and we already know that the nucleus is also positively charged. From our earlier lessons in Physics we already learnt that like charged repel and unlike charges attract one another. Therefore if the positively charged nucleus occupies a larger volume within the atom then the most of alpha particles will be deflected as like charges repel, however Rutherford found that most of the alpha particles passed straight through the gold foil without any deflection which suggested that nucleus occupies a small volume within the nucleus compared to the size the atom.

2. Most of the region inside an atom is empty as most of the alpha particles went straight through the gold foil without getting deflected.

                             

Figure 4: Rutherford's Nuclear Model of an Atom

                                       

Rutherford  published his famous paper on the 'Nuclear Model of Atom', in which he postulated that the 'nucleus' occupies the centre of the atom and nearly all of the mass of the atom is concentrated in the nucleus, a possible reason for this is that nucleus contains both protons and neutrons which when taken together itself is a huge mass in comparison to the mass of electrons moving around the nucleus in 'circular orbits'. Rutherford believed that electrons move around the nucleus in circular orbits..."a big theoretical mistake..."

Though all of his conclusions were true, he was not right about this 'circular orbit concept'...

But...why???🤔

You know any object moving in circular orbits around a fixed mass, here. 'the nucleus', then due to its circular motion it gets accelerated. We know electrons are charged particles, when these electrons get accelerated it loses energy. Finally when the electron loses all of its energy then it will in turn fall into the nucleus...

Still...what is the problem???🤔

We know atom is quite stable so if this conclusion drawn by Rutherford were true, it would question the very concept that 'atom is stable'...😮

Sir Ernest Rutherford won the Nobel Prize in Chemistry in 1908. The following is the citation from official website of the Nobel Prizes which states why he was awarded with the Nobel Prize...

''The Nobel Prize in Chemistry 1908 was awarded to Ernest Rutherford "for his investigations into the disintegration of the elements, and the chemistry of radioactive substances.''

His pioneering works in field of atomic structure and study of the nucleus earned him the title, "The Father of Nuclear Physics"...

                                                     

                                                  

Information Credits: Referred the NCERT textbook Class 9 for some clarifications.

Picture Credits: All the images shown in this blog were taken directly from Wikimedia Commons