Recent discussions in TPT have considered the pros and cons of an early introduction of students to modern physics.1–4 In this regard, appropriate experiments with classical waves can help students understand some important but counterintuitive aspects of modern physics. I recently taught a summer course that introduced high school seniors who had graduated with some background in physics and algebra to aspects of quantum physics and relativity. In this paper I'll describe a simple experiment I used to introduce these students to uncertainty principles in quantum physics.

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Ruth
Howes
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Modern physics—Guest editorial
,”
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Art
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Teaching ‘modern’ physics in introductory courses
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Ludwik
Kowalski
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Teaching advanced physics: Who, when, and how?
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).
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Michael
George
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Response to teaching modern physics
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L.
Nieves
,
G.
Spavieri
,
B.
Fernandez
, and
R. A.
Guevara
, “
Measuring the Planck constant with LED's
,”
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35
,
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(Feb.
1997
). Following this experiment with the one I discuss gives the students a feeling as to why the tiny (but nonzero) value found for h has profound consequences.
6.
Experiments and discussion related to ΔPxΔx ⩾ h include energy estimates of particles in bound systems such as electrons in atoms or nucleons in a nucleus, and divergence of laser beams and the effect of a beam expander as well as diffraction of light or particles passing through a slit. Applications of ΔEΔt ⩾ h include: (1) differences in the width of emission lines produced by high and low pressure sodium lamps related to lifetime (Δt) changes, and (2) discussion of Mossbauer-effect experiments such as gravitational red shift related to source height above the Earth's surface. (Here large Δt in nuclear decay gives small and very useful ΔE.)
7.
I used a ULI II interface with Logger Pro software from Vernier Software to collect data in this experiment. 13979 SW Millikan Way, Beaverton, OR 97005-2886; 503-277-2299, http://www.vernier.com.
8.
Mathcad software for Windows is available at academic discounts from MathSoft Engineering and Education Inc., Boston, MA; 800-628-4223, http://www.mathsoft.com.
9.
K. Steiglitz, A Digital Signal Processing Primer (Addison-Wesley, New York, 1996).
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