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Stern–Gerlach experiment
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Beam splits by spin orientation.
Silver atoms passing through a non-uniform magnetic field split into two beams, not a continuous smear, showing spin quantisation.
1922 experiment.
Sequential measurements show non-commuting components.
In more detail
The Stern-Gerlach experiment sent silver atoms through an inhomogeneous magnetic field, splitting them into two beams. This revealed quantised spin of the electron.
Real-world uses
- It demonstrated quantisation of angular momentum in atoms.
- Spin-based quantum technologies build on this result.
- Physicists used the Stern–Gerlach experiment to show that electron spin is quantised, with only two outcomes.
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Frequently asked questions
Why two beams and not a continuous spread?
Because the spin of the electron can only take two values along any axis.
What is an inhomogeneous field used for?
It applies a force depending on the spin orientation, separating the beams.
Why did the beam split into two?
Spin is quantised, so each atom's magnetic moment points in only one of two possible directions when measured.
Related topics in Quantum Mechanics
Quantum numbers · Atomic orbitals · Electron spin · Pauli exclusion principle · Fermions and bosons · Identical particles