Tesla and the photoelectric effect

[Omegatron]

So someone pointed me to a patent of Tesla's (or two, rather, but basically the same thing):

* US Patent 685, 957: Apparatus for the utilization of radiant energy

* US Patent 685, 958: Method of utilizing radiant energy

(You need a TIFF viewer and then click on the "images" link.)

They said that this is a rudimentary solar cell. I said "no way!", but then I looked at it more in depth, and it does seem to be an implementation of the photoelectric effect for collecting solar energy.

UV or X-rays of higher energy (frequency) than the work function of the metal (energy required to knock an electron from a metal's surface to infinity) knock electrons off the metal and give it a positive charge. Connecting it to a capacitor and then to the ground allows you to charge the metal plate up a lot more than before, because the capacitor "condenses" charge into a smaller area/volume (hence the older word "condenser" which is still used in every language other than English. does anyone know who invented the term "capacitor?")

So I built a little thing to test it. I took a coat hanger and sanded off the varnish, and soldered one piece to the negative side of a 4700 uF electrolytic capacitor. I soldered the other piece of coat hanger to the other side and made a triangle shape. Then I scrunched up an aluminum pie plate type thing (like thick foil) on the triangle thing to make the "collecting" plate.

I stuck the straight piece maybe three inches into the ground so the big plate is on top, horizontal, and shading the rest. Anyway, after leaving it like that for a few minutes in bright sunlight I measured -27 mV. :-(

Just waving the probes around in the air makes it display 200 mV or so. Plus, the voltage on the plate is supposed to be positive because it has had electrons removed from it. So my experiment was a failure.

So there are some possibilities that I see for why mine didn't work:

* Photoelectric effect doesn't work in air (because the electrons bounce off air molecules until they have slowed down enough to fall back onto the plate?)

* Didn't leave it there long enough. (I felt kind of silly measuring a lasagna lid. Gotta find a place with no one around.)

* Capacitor thing with one end stuck in the ground doesn't really work that way. (I brought this up in another thread.)

* Because the aluminum is covered in oxide (although oxide coatings reduce the work function for vacuum tube filaments, maybe they prevent photoelectric effect from working at all?)

* I know pointiness and crinkles change the behavior of a charged metal object. It is easier for them to give off electrons at sharp points? Not sure if this has anything to do with it.

It seems like it should work, though, since a similar experiment like this works: See Figure 3 or http://www.press.uillinois.edu/epub/books/brown/images/fig5.3b.gif .

Differences:

* It's in a vacuum

* There is another plate to catch the electrons that have been kicked out

* It operates in a more standard circuit-type way, whereas Tesla's is more a "unidirectional", "broken-circuit" charged object type of thing.

 

[Vailanor]

So, it seems like there is still something that needs to be worked out to make this work in air. Any ideas?

 

[Graeme Robinson]

It is interesting to see that Tesla, known for his work in electricity and magnetism, also had patents related to the utilization of radiant energy. The patents you mentioned do seem to describe a rudimentary solar cell using the photoelectric effect. The photoelectric effect is the process in which electrons are emitted from a material when it is exposed to electromagnetic radiation, such as UV or X-rays. This is the same phenomenon that is utilized in modern solar cells to convert sunlight into electricity.

Your experiment with the coat hanger and aluminum plate is a creative way to test this concept, but there are a few factors that may have affected your results. As you mentioned, the photoelectric effect is more efficient in a vacuum, so the presence of air may have hindered the process. Additionally, the oxide coating on the aluminum may have also played a role in reducing the efficiency of the photoelectric effect.

Another important factor to consider is the design and setup of the experiment. In the patents, Tesla describes a specific configuration of the metal plates and the capacitor, which may be crucial for the proper functioning of the device. It is also possible that leaving it in the sunlight for a longer period of time may have yielded different results.

Overall, it is fascinating to see Tesla's ideas and inventions extending beyond his well-known work in electricity and magnetism. While his patents may not have been as successful as modern solar cells, they still demonstrate his innovative thinking and understanding of the photoelectric effect.