1) The Photoelectric Effect and Planck's constant h

Polished presentation (pdf): photoeffect.pdf

This page contains links to four pages of lecture notes to accompany the high-school lecture and demonstration of the measurement of Planck's constant using the photoelectric effect. The photodiode required is of a vacuum tube type, a semiconductor photodiode will not do (its photovoltage has more to do with how the semiconductor works rather than the energy of the photons). A picture of a couple of phototubes is given here P40 , our tube cetron was purchased from Sphere Research in BC (via the www).

The lecture notes are four pages of jpg files: page 1 , page 2 , page 3 , page 4 , page 5 .

For light sources we use a halogen desklamp with two power settings (to demonstrate the independence of the photovoltage on the light intensity) combined with 10-nanometer bandwidth interference filters at 400-650 nm with 50 nm intervals. In addition we use intense LEDs, which have typical bandwidths of 50 nm. Such LEDs are available in Toronto from Active Surplus (Queen St W), and also from some Radio-Shack outlets.

We measure the photovoltage directly with a high-impedance voltmeter (10 Gigohms), an instrument worth several thousand dollars (HP 3457 A). This is simpler than the usual stopping voltage measurement, which requires a simple voltmeter, and a fancy ammeter (sub-nanoampere range).

The results can be analyzed with a Maple worksheet. An HTML version which discusses one set of data taken: Planck constant

My department's webpage: Physics and Astronomy, York University .

A second 50-min lecture with a demonstration of Fraunhofer single-slit diffraction:

2) Feynman's sum over paths method to understand wave-like behavior of photons

The lecture notes are three pages of jpg files: page 1 , page 2 , page 3 .

There are several Java applets that can be used to compute the interference patterns. They are embedded in html-pages linked to our department webpages: Physics Tutorials

The demonstration uses Vernier calipers and a powerful green laser pointer to display a Fraunhofer (single-slit) diffraction pattern on the wall. Pictures taken with a digital camera (red and green laser pointers) will also be shown: calipers and laser pointer