File LO1-Lec2
Lecture Content and Activity Notes:
• Start with classical E&M field and showed the total E&M spectrum and the very
small region of visible light in the whole thing. Using f = c relationship showed that
E=hc/ .
• Do the calculation for 550 nm light, which is the peak sensitivity for a typical
human being. The answer of about two electron volts is then discussed as the order of
magnitude for optical processes. Compare this to thermal processes (room temperature
is only about 0.02 eV) and chemical processes which are typically tenths of an eV.
• Show a dim incandescent light bulb and turned it up bright to show that even as a
bright light it would not discharge a charged electrometer. Showed Planck's law fit to the
data.
• Do the Photoelectric demo again and show the influence of glass on the UV light
source…light as photons.
• Show three gas tube light sources and distribute good diffraction gratings for the
students to use to look at the spectra. Show the Balmer series and discuss the story of
Balmer guessing the integer number equation and give the original Balmer equation.
Reference: The Balmer story is told by Holton and Roller in Foundations of Modern
Physical Science, Section 33.5, pages 697 - 699. Addison-Wesley Publishing Co., Reading,
MA 1958. It is also available in electronic format on the Physics InfoMall CD-ROM.
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