@AbdooMs EG The term spin is misleading. Particles are not spinning. They have an intrinsic angular momentum. In other words, particles will do things that are only possible if they were spinning, but they are not. For example: a spinning charged particle when put on a magnetic field will start a precession in its axis, like the earth does in the gravitacional field. But the precession is a reaction of a spinning object to a torque, a force. So a particle will react to a torque of the magnetic field and start doing its precession, as if it was a spinning object, despite the fact its not spinning at all. *I'm repeating words because my english is limited.
The only video that goes deep into the details of MRI, to the extent of explaining its quantum mechanics! As a medical student I'm very satisfied to have found this video, thank you.
"We call this property spin." "But it isn't spinning." "We won't go into details why it isn't actually spinning." That really doesn't explain anything.
Kirtikumar Goswami Its the number of spins they need to do before backing to the situation of "balance". But its not really a spin. A new word need to be created. Its not really spinning.
the nucleons can have orbital angular momentum, which comes in units of 0, 1, 2, 3, .... and is added to the spin. But the quantum mechanical addition of angular momentum is non trivial. See: Racah Algebra.
"the wavefunction of 2 or more identical fermions must be antisymmetric (change sign) under the interchange of any two particles", is the correct statement. So that of course rules out a single proton occupying a single state, as in the cartoon. Moreover, in nuclear physics, the proton and neutron are identical particles with different isospin quantum numbers.
(non text book answer, but makes more sense) Spin is the stationary angular momentum of a particle. It also may define mass. Something like a flywheel spinning with some rpm (frequency), but if you convert that angular momentum to linear momentum, then there is linear translation with the same energy (frequency). With subatomic particles, when they are annihilated, they become photons with a wavelength and translate at light speed. When a photon becomes a particle (say.. a fermion) that 'lightspeed' linear momentum becomes angular momentum or mass (spin). This property may also involve a gravitomagnetic field but again, not 'approved' statements from the standard model which does have its limitations btw.
It's called spin because it gives magnetic polarity (or angular momentum) to the particle. N & S so we can say North is up or North is down. A bit like a coil of wire wrapped around a nail. The coil isn't spinning but the coil does go around the nail.
When our title is the law maker we legislate laws. When we are under or ill qualified for the job the laws we past don’t hold water and people will experience implementation problem. The third generation law makers can only make new laws around the prevailing laws. 1st gen legislation - electron 1st gen problem - contradicts atomic physics 2nd gen legislators - Einstein, Hubble ... 2nd gen problem - time isn’t absolute, space isn’t absolute, black holes and contracting universe, red shift expanding universe. 3rd gen legislation - quantum mechanics. 3rd gen problem - virtual physics to a virtual reality.
Thanks a lot. But may I ask why at the end you say the spin can be "multiple of 1/2 or a whole number" when in the explanation as I understand can only be 1/2 or 1, plus or minus.
Great video, but I have my reservations judging only the teaching and not the knowledge of the lecturer. It is a video of course and I cannot interrupt the lecture to ask questions as I would in a class room. The semantics are generating more questions at times and there is also no mention of spdf sub orbits. When you use C for example, one may think that each level holds 2 protons if they have no knowledge of spdf orbits (they will assume that there are three levels instead of 2). I appreciate your effort to teach. Teaching is a different league on its own and is independent of how much knowledge we posses for our selves. You have my respect for your time and creation.
What’s the difference between UUD and UUUe regarding Protons? Likewise, UDD and UUUee for Neutrons? The latter representation suggests a 0s orbital that allows up to two electrons to “orbit” much closer to three Up quarks. This also allows for a better representation for nuclear spin.
Two unifomly charged identical solid sphere of same radius are revolving about parallel diameters with same angular speed in opposite direction.The magnetic dipole moment of arrangement is zero .A uniform magnetic field is applied parallel to axis of rotation,after applying field net magnetic dipole moment of arrangement. Sir, how do you solve this?
The example with the ladder is bad. Because in the nucleus, not every energy level is filled with 2 pairs of protons and neutrons. It goes like : 1S1/2 (takes up to 2 protons and 2 neutrons), 1P3/2 (takes up to 4 of each) 1P1/2 etc. This video will confuse someone who is trying to understand this model for the first time.
Like aether's magnetic field, all magnetic fields. Rotate in one direction, from one side CW and from the opposite pole CCW. Fields together = 1 field. 1+1=1, magnets and magnetic field of aether.
It's all bolony because it's all a matter of how it's all observed. If you standing upright it may be observed that it has an up spin, but if you look at it hanging upside down that same particle from the view point of the observer will be a down spin. and if the observer stand up he will again view that exact same particle as an up spin particle. And in free space where there is no up or down reference you could never tell. So an upright observer and an upside down observer will see two different spins of the exact same particle. It's all a matter of frame of reference.
That is correct, the axis of quantization (defining up or down) is totally arbitrary. Had you picked left or right, then the states are right = (up + down)/sqrt(2) and left = (up - down)/sqrt(2)...so, so what? A pure superposition of up or down is always "up" or "down" in a different coordinate system (see: The Bloch Sphere). However, once you turn on an external magnetic field, that symmetry is broken. There is now a preferred direction in space and the eigenstates of the hamiltonian (H) are up and down (where "up" is _defined_ by the magnetic field). Now you can do quantum mechanics with a non-diagonal hamiltonian and work with spin left and right and still get the right answer, but it's a lot messier than just using the states that diagonalize H.
that explains the summation of spin, yet does not define spin. Some by angular momentum, Hawking disputed this. Hawking (a brief history of time) said it was the number of rotations to look the same. That would require more than 3 spatial dimensions for spin 1/2 leptons. So what is the angular momentum of a 0 point particle? I know it works, from electrons to black holes but i have never seen a good definition of spin.
Hawking's definition is good. A spin-1 particle (a vector) must be rotate once to be the same. A spin-2 particle(tensor), needs to be rotate 180 degrees to be the same...like your polarized sun glasses. There is a alignment, but no arrow picking up or down. A spin 1/2 particle (spinor) needs to be rotate 720 degrees...it's just mathematical fact when dealing with SU(2), which double covers the group of "normal" rotations, SO(3). So all particles must respect the symmetries of space, and SU(2) is one of them. Oh, and a spin-0 particle (a scalar, like an alpha particle), is absolutely perfectly spherical, so you cannot rotate it. It is meaningless as it is unchanged by rotations.
Surely free (singe- or unbonded) electrons, atoms or nucleons can freely flip or turn to orientate themselves to the magnetic field as they choose. If so Spin up or spin down (2:45) would appear to be the same thing, there is no other difference illustrated. (I see this same description everywhere, I may be thick, but it makes no sense at all to me.)
Spin up or spin down is sort of the same thing in the sense that you are talking about the same axis of orientation, a single dimension of space. What happens whenever a charged particle is in a sufficiently strong magnetic field is that it will always align itself to that magnetic field either 'towards the north' (spin up) or 'towards the south' (spin down). They cannot freely choose any kind of middleground in that particular spatial dimension determined by their position relative to some strong magnetic field, they are however plenty free to do whatever they want in the remaining two spatial dimensions you aren't looking at. Also, in more complicated things like a big atom their component parts can do whatever they want as long as the average alignment of them all conforms to the magnetic field (and the magnetic field needs to be stronger to override the substantial forces those nuclear particles already pull on each other). Actually even in a single hydrogen atom it gets complicated as that single electron can compensate for some "off angle" in it's spin with an equal and opposite "off angle" in it's orbital.
i hv a question sir: ca we divide neutron further? as we can devide atom.. if not then, why shoud it be neutral? and further i think, inside a neutron, there is a big universe.
Because a spin J particle can have spin states with Jz = (-J, -J+1,..., J-1, J). So with J=1/2, Jz = +/ - 1/2. The reason? The representation theory of SU(2).
Molecules are a little more complicated but the short answer is no. In essence it’s the fundamental particles that have spin, ie quarks, electrons. Protons and neutrons have resultant spin due to their quark composition. Nuclei have net spin due due to Pauli exclusion principle. The result is always none, up, or down spin. Molecules are 3D and arranged based on bonds and repulsions between atoms and so no chance really of a net spin up or down. That’s the way I see it but I’m happy to be corrected Some serious quantum physics here.
11:00 is clearly a false construct, the images don't match the labels & the statements are false, incomplete and ambiguous. I won't even listen to what the person is saying here.
+Liviya Varghese it is my understanding that you cannot use nmr with atoms of spin =0, such as C12. However, if you know that that element has natural isotopes, then you can you use that to your advantage. So C13 is present in a carbon sample and has a spin and so could be used for NMR spectroscopy.
+Kamdar Sudhanshu not sure what you mean. The two nucleons in the nucleus are the protons and neutron. Only the proton has charge. Their arrangement is determined by the balance between electrostatic repulsive forces and the attractive strong nuclear forces.
