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He battled with Einstein about Quantum Physics, and WON
Niels Bohr was a genius in his own right, contributing hugely to the developing theory of quantum mechanics. In this video, we take a look at what is probably his most famous work - the Bohr Model of the atom.
Before Bohr came along, scientists suspected that atoms contained scattered regions of positive charge, with small negative electrons distributed throughout. This was known as the Plum Pudding model.
Ernest Rutherford, conducting the Gold Foil / Geiger Marsden experiment with his students, realized that this could not be right. When positive alpha particles were fired at a thin gold foil, instead of them all passing right through with minimal deflection, something curious was observed.
Some passed through with minimal deflection, others passed through with large deflections of around 90 degrees, and a very small proportion actually came back almost towards the detector - at nearly 180 degrees of deflection. Rutherford said this was like firing a shell at a piece of tissue paper, and the shell coming back to hit you - very unexpected.
He realized that the positive regions in the atoms must have been distributed over very small regions, with all the positive charge being concentrated there. So when the alpha particles came very close to these regions, they would deflect hugely. A glancing blow resulted in the roughly 90 degree deflections. However because atoms were mainly empty space, the large majority of alpha particles passed right through the gold foil.
Rutherford then developed his Planetary model - with electrons orbiting the positive region known as the nucleus. This was great, but had problems of its own. If electrons were to orbit the nucleus, then they would be accelerating due to their constant change in direction.
The physics of charged objects told us that accelerating charges would radiate, and lose energy. This can be seen from the Larmor formula, which calculates the given power radiated by a charge at a given acceleration.
Therefore, Rutherford's atoms should have been unstable, with the electrons radiating energy away and spiraling inward to the nucleus. This is where Bohr came in.
Bohr realized that there was something holding electrons specific distances away from the nucleus. He called these "allowed" locations "energy levels". His model explained why electrons did not radiate constantly, and also explained the emission spectra observed from atoms. Instead of emitting radiation at all frequencies as electrons spiraled, we would only see specific emissions based on the differences in energies of the allowed levels, whenever electrons transitioned inward.
He also found a wonderfully neat mathematical relationship that explained where the "allowed" energy levels were in relation to the nucleus. He found that an electron's angular momentum in a particular energy level had to be a multiple of the Reduced Planck Constant - a very important constant in quantum mechanics.
The angular momentum of the electron, dependent on the mass and speed of the electron, as well as the radius of the path it was moving on, could be calculated by setting the electric attraction force between the electron and the nucleus to be equal to the centripetal force needed to keep it moving on that orbit. From there, with a bit of math, it was possible to calculate exactly where (i.e. at what radii) the allowed energy levels could be found!
Thanks for watching, please do check out my links: MERCH - https://parth-gs-merch-stand.creator-spring.com/ INSTAGRAM - @parthvlogs PATREON - patreon.com/parthg MUSIC CHANNEL - Parth G Music Here are some affiliate links for things I use! Quantum Physics Book I Enjoy: https://amzn.to/3sxLlgL My Camera: https://amzn.to/2SjZzWq ND Filter: https://amzn.to/3qoGwHk Chapters:
0:00 - Niels Bohr - An Introduction
1:12 - The Plum Pudding and Planetary Models of the Atom
3:16 - The Big Problem with Rutherford's Model
5:14 - The Bohr Model of the Atom
6:17 - What Are the "Allowed" Energy Levels?
8:31 - More About Bohr
He battled with Einstein about Quantum Physics, and WON
Niels Bohr was a genius in his own right, contributing hugely to the developing theory of quantum mechanics. In this video, we take a look at what is probably his most famous work - the Bohr Model of the atom.
Before Bohr came along, scientists suspected that atoms contained scattered regions of positive charge, with small negative electrons distributed throughout. This was known as the Plum Pudding model.
Ernest Rutherford, conducting the Gold Foil / Geiger Marsden experiment with his students, realized that this could not be right. When positive alpha particles were fired at a thin gold foil, instead of them all passing right through with minimal deflection, something curious was observed.
Some passed through with minimal deflection, others passed through with large deflections of around 90 degrees, and a very small proportion actually came back almost towards the detector - at nearly 180 degrees of deflection. Rutherford said this was like firing a shell at a piece of tissue paper, and the shell coming back to hit you - very unexpected.
He realized that the positive regions in the atoms must have been distributed over very small regions, with all the positive charge being concentrated there. So when the alpha particles came very close to these regions, they would deflect hugely. A glancing blow resulted in the roughly 90 degree deflections. However because atoms were mainly empty space, the large majority of alpha particles passed right through the gold foil.
Rutherford then developed his Planetary model - with electrons orbiting the positive region known as the nucleus. This was great, but had problems of its own. If electrons were to orbit the nucleus, then they would be accelerating due to their constant change in direction.
The physics of charged objects told us that accelerating charges would radiate, and lose energy. This can be seen from the Larmor formula, which calculates the given power radiated by a charge at a given acceleration.
Therefore, Rutherford's atoms should have been unstable, with the electrons radiating energy away and spiraling inward to the nucleus. This is where Bohr came in.
Bohr realized that there was something holding electrons specific distances away from the nucleus. He called these "allowed" locations "energy levels". His model explained why electrons did not radiate constantly, and also explained the emission spectra observed from atoms. Instead of emitting radiation at all frequencies as electrons spiraled, we would only see specific emissions based on the differences in energies of the allowed levels, whenever electrons transitioned inward.
He also found a wonderfully neat mathematical relationship that explained where the "allowed" energy levels were in relation to the nucleus. He found that an electron's angular momentum in a particular energy level had to be a multiple of the Reduced Planck Constant - a very important constant in quantum mechanics.
The angular momentum of the electron, dependent on the mass and speed of the electron, as well as the radius of the path it was moving on, could be calculated by setting the electric attraction force between the electron and the nucleus to be equal to the centripetal force needed to keep it moving on that orbit. From there, with a bit of math, it was possible to calculate exactly where (i.e. at what radii) the allowed energy levels could be found!
Thanks for watching, please do check out my links: MERCH - https://parth-gs-merch-stand.creator-spring.com/ INSTAGRAM - @parthvlogs PATREON - patreon.com/parthg MUSIC CHANNEL - Parth G Music Here are some affiliate links for things I use! Quantum Physics Book I Enjoy: https://amzn.to/3sxLlgL My Camera: https://amzn.to/2SjZzWq ND Filter: https://amzn.to/3qoGwHk Chapters:
0:00 - Niels Bohr - An Introduction
1:12 - The Plum Pudding and Planetary Models of the Atom
3:16 - The Big Problem with Rutherford's Model
5:14 - The Bohr Model of the Atom
6:17 - What Are the "Allowed" Energy Levels?
8:31 - More About Bohr
