---
title: "Electron Spin and the Stern-Gerlach Experiment"
description: "A beam of silver atoms splits into exactly two in a non-uniform magnetic field, which no orbital motion can explain. Electrons carry an intrinsic angular momentum with only two possible projections."
canonical: https://lightmysky.com/learn/science/electron-spin-and-the-stern-gerlach-experiment-mt_HVFLoNe6wk
source: https://lightmysky.com/learn/science/electron-spin-and-the-stern-gerlach-experiment-mt_HVFLoNe6wk.md
retrieved: 2026-09-12
---

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# Electron Spin and the Stern-Gerlach Experiment

A beam of silver atoms splits into exactly two in a non-uniform magnetic field, which no orbital motion can explain. Electrons carry an intrinsic angular momentum with only two possible projections.

Subject: Science · Area: Quantum & Modern Physics · Ages 21 to 22
Page: https://lightmysky.com/learn/science/electron-spin-and-the-stern-gerlach-experiment-mt_HVFLoNe6wk

## Ready when they can

- Describes the experiment and why two beams rule out a classical magnetic moment
- States the allowed spin projections and the associated magnetic moment
- Explains fine structure as a coupling between spin and orbital motion

## Lesson: Two spots, no smear

Stern and Gerlach sent silver atoms through a nonuniform magnet and got exactly two beams. A classical magnet could tilt at any angle and would smear into a band, so two sharp spots mean the underlying magnetism has only two settings. No orbital motion can explain that pattern, since orbital projections offer more than two tilts.

The explanation is electron spin, an intrinsic angular momentum with quantum number one half and only two projections: plus or minus h bar over 2, called up and down. Its magnetic moment steered the two beams apart, and it joins the three hydrogen numbers as a fourth degree of freedom.

**Example.** Silver works because each atom carries one unpaired outer electron whose spin decides the deflection. Up goes one way and down goes the other, painting two spots. A classical spray of tilts would have painted a smear instead.

**Tip.** Spin never acts alone: its magnetism pushes and pulls on the orbital magnetism, a coupling that shifts levels by small amounts called fine structure. Each Bohr line turns out to be a close pair split by that handshake. Spectra pages show the pairs; the magnet showed the cause.

**Recap.** Two beams prove two settings, and spin names the extra magnet.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Charged Particles Moving in a Magnetic Field](https://lightmysky.com/learn/science/charged-particles-moving-in-a-magnetic-field-mt_evuhZ6cSfI)
- [Orbital Angular Momentum and the Quantum Numbers](https://lightmysky.com/learn/science/orbital-angular-momentum-and-the-quantum-numbers-mt_OXlbat0vat)

## Opens up

- [The Exclusion Principle and Multi-Electron Atoms](https://lightmysky.com/learn/science/the-exclusion-principle-and-multi-electron-atoms-mt_4tLa-3Av0A)
- [Angular Momentum from Its Commutation Relations](https://lightmysky.com/learn/science/angular-momentum-from-its-commutation-relations-mt_u0y20XJh-v)