---
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: 2026-11-12
---

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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: orbital projections come in odd numbers, 2l plus 1, and silver's outer electron has l equals 0, which alone would give one undeflected beam.

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.

Once the electron also orbits, with l above zero, spin does not act alone: its magnetism pushes and pulls on the orbital magnetism, a coupling that shifts levels by small amounts called fine structure. Lines that looked single turn out to be close groups, often pairs, split by that handshake.

**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

- [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)