The Stern-Gerlach experiment shows that the spatial orientation of the angular momentum is quantized. This shows that the atomic scale system has intrinsic quantum properties. In the original experiments, silver atoms were sent through a spatially varying magnetic field, which deflected them before they hit a detector screen, like a sliding glass. If the particles have a magnetic moment, the magnetic field gradient diverts them from a straight path. The display shows separate accumulated dots rather than continuous distributions, due to the nature of the spin quantum. Historically, this experiment was crucial in convincing physicists of the quantitative reality of angular momentum in all atomic scale systems.
The first attempt was made by German physicist Otto Stern and Walther Gerlach, in 1922.
Video Stern-Gerlach experiment
Description
The Stern-Gerlach experiment involves sending a beam of silver atoms through an un homogeneous magnetic field and observing their deflection.
The results show that the particles have intrinsic angular momentum which is very similar to the angular momentum of a classically rotating object, but requires only a certain quantized value. Another important result is that only one component of the particle spin can be measured at a time, meaning that the measurement of rotation along the z axis destroys information about particle rotation along the x and y axes.
Experiments are usually performed using electrically neutral particles such as silver atoms. This avoids a large deflection on the path of charged particles moving through the magnetic field and allowing effects that depend on the spin to dominate.
If the particle is treated as a classical spinning magnetic dipole, it will be precess in the magnetic field because of the torque given the magnetic field on the dipole (see torque induced precession). If moving through a homogeneous magnetic field, the force applied at the opposite end of the dipole will cancel each other and the path of the particle is not affected. However, if the magnetic field is not homogeneous then the force at one end of the dipole will be slightly larger than the opposing force at the other end, so there is a total force that deflects the particle trajectory. If the particles were classical spin objects, one would expect the distribution of their spin angle momentum vectors to be random and continuous. Each particle will be deflected by an amount proportional to its magnetic moment, producing some density distribution on the detector screen. Instead, the particles passing through the Stern-Gerlach apparatus are bent up or down by a certain amount. This is a measurement of the observable quantum now known as the rotation angular momentum, which indicates the probability of measurement results which can be observed to have separate set of point values ​​or point spectra.
Although some discrete quantum phenomena, such as atomic spectra, were observed much earlier, the Stern-Gerlach experiment allowed scientists to observe the separation between discrete quantum states for the first time in the history of science.
Now, it is known that, theoretically, quantum angular momentum of any type has a discrete spectrum, which is sometimes expressed improperly as "quantized corner momentum".
Experiments using particles with 1 / 2 or - 1 / 2 spinning
If an experiment is carried out using charged particles such as electrons, there will be Lorentz forces that tend to deflect the path in a circle (see cyclotron movement). This force can be canceled by an electric field with a corresponding magnitude oriented across the charged particle path.
Elektron adalah partikel spin- 1 / 2 . Ini hanya memiliki dua kemungkinan nilai momentum sudut putaran yang diukur sepanjang sumbu apa pun, atau , fenomena mekanika kuantum murni. Karena nilainya selalu sama, ia dianggap sebagai properti intrinsik elektron, dan kadang-kadang dikenal sebagai "momentum sudut intrinsik" (untuk membedakannya dari momentum sudut orbital, yang dapat bervariasi dan bergantung pada kehadiran partikel lain).
If we connect some Stern-Gerlach apparatus (rectangles containing S-G ), we can clearly see that they do not act simple selectors, but alter the observed state (as in the polarization of light). In the three S-G systems shown below, the cross-cross boxes indicate the blocking of the given output. Blocked output is the only source for the next S-G device in sequence.
The top system shows that when z is passed through the identical and second S-G apparatus, only z is visible at the output, as expected.
The middle system shows that the z input can be ordered on x-axis which produces x and x-output.
The lower system feeds the output x into the third S-G apparatus and shows that it is ordered on z-axis to generate z and z-output. Given that the input to a second S-G device consists only of z, while the output of the third contains z- and z, it can be inferred that the S-G device must change the state of the particle passing through it.
Maps Stern-Gerlach experiment
History
The Stern-Gerlach experiment was conceived by Otto Stern in 1921 and undertaken by him and Walther Gerlach in Frankfurt in 1922. At that time, Stern was the assistant to Max Born at the Institute of Theoretical Physics Institute in Frankfurt, and Gerlach was an assistant at the Institute for Experimental Physics university the same one.
At the time of the experiment, the most common model for describing atoms is the Bohr model, which describes electrons as circling positively charged nuclei only to certain discrete atomic orbitals or energy levels. Because electrons are quantified into only a certain position in space, separation into different orbits is called the quantization of space. The Stern-Gerlach experiment was intended to test the Bohr-Sommerfeld hypothesis that the direction of the silver atomic momentum is quantized.
Note that experiments were conducted several years before Uhlenbeck and Goudsmit formulated their hypothesis about the existence of an electron spin. Although the results of the Stern-Gerlach experiment were then in accordance with predictions of quantum mechanics for spin- 1 / 2 particle, the experiment should be seen as corroborating evidence Bohr-Sommerfeld.
In 1927, T.E. Phipps and J.B. Taylor reproduces the effect of using hydrogen atoms in their ground state, eliminating any doubts that might be caused by the use of silver atoms. However, in 1926 the non-relativistic Schrö¶dinger equation had incorrectly predicted the magnetic moment of hydrogen to be zero in its basic state. To correct this problem, Wolfgang Pauli introduces "by hand", so to speak, 3 Pauli matrices are now wearing his name, but which Paul Dirac later pointed out in 1928 to be intrinsic in his relativistic equations.
The experiment was first performed with an electromagnet that allows a non-uniform magnetic field to be ignited gradually from a zero value. When the field is zero, the silver atom is deposited as a single band on a detecting glass slide. When the field was made stronger, the center of the band began to widen and eventually split into two, so the glass-slide image looked like lip-print, with aperture in the middle, and closure at both ends. In the middle, where the magnetic field is strong enough to split the light in half, statistically half of the silver atoms have been deflected by the field inequality.
Importance
Source of the article : Wikipedia
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