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Two spots, no smear

Science · Quantum & Modern Physics · ages 21-22

Name ______________________ Date ____________

Why did two beams rule out a classical magnetic moment?
- Classical moments always line up with the field, giving one beam
- Classical moments tilt at any angle and would smear
- Magnets cannot deflect atoms
What pattern did the silver beam form?
- A smear from every possible tilt
- Exactly two sharp beams
- A single spot
What are the allowed electron spin projections?
- Any value between minus h bar and plus h bar
- 0 and h bar
- Plus or minus h bar over 2
Fine structure is the tiny splitting of lines from spin orbit coupling.
Circle one: True False
Why silver atoms?
- Each carries one unpaired electron whose spin decides the kick
- Silver has no electrons
- Silver melts magnets
Many lines that looked single turn out to be close pairs. What causes the splitting?
- Spin orbit coupling
- Extra protons
- Collisions between atoms
A friend claims the two spots are just orbital m values of silver. What is wrong?
- Orbital projections come in odd numbers, never exactly two
- Spin never pushes on anything in a magnetic field
- Silver's orbital m values really do give exactly two tilts
Could you explain why the silver beam splits into two and not into a smear?
- Orbital tilts are continuous
- Only two spin settings exist, so only two deflections occur
- The magnet has two poles

Answer key

For grown-ups. Fold this page away before handing over the rest.

Classical moments tilt at any angle and would smear · Any tilt allowed means a continuum of deflections, which is a band and not two spots.
Exactly two sharp beams · The lopsided magnet split the beam into two, revealing two magnetic settings.
Plus or minus h bar over 2 · Spin one half allows only up and down along the chosen axis.
True · Spin and orbital magnets tug on each other and shift levels by small amounts.
Each carries one unpaired electron whose spin decides the kick · The lone outer spin dominates the atomic magnet that the field grabs.
Spin orbit coupling · The coupling energy separates the line into close partners.
Orbital projections come in odd numbers, never exactly two · Orbital projections come in odd numbers, 2l plus 1, and silver's outer electron has l equals 0, so orbital motion cannot make exactly two beams.
Only two spin settings exist, so only two deflections occur · Two allowed magnetisms give two forces, hence two beams.