Photoelectric Effect
From MariachiWiki
A simple demonstration of the Photoelectric Effect can be done using an electroscope. This is a popular experiments usually performed in High Schools. It can also be found in numerous internet experiment sites. The following is a low-cost version with stuff you can buy.
The general idea is that you charge an electroscope negatively, i.e. put electrons in a metal with low work function. Zinc is the preferred metal. It can be purchased from and art supply outlet or a store which sells batteries. Although the following items can be used as a substitution:
- Zinc plated steel - from Home Depot
- Take a D-Cell battery and open it carefully. The metal on the outside is zinc.
- Marine stores usually sell zinc (but I'd never went to one)
The one we used was acquired from VanDykes Restorers. The product is Zinc Pie Safe Blanks 10" x 14", part number 02370080, and costs about $6.00. This might be a little much for one person's experiment.
Warning: Zinc usually oxides easily, so have a sand paper handy to scrape its surface.
Mount the zinc plate on top of the electroscope. It is important to make sure that there is good contact between them. Then negatively charge the electroscope. This can be achieved in a number of ways. Good question for the reader....
To discharge the electroscope by the photoelectric effect you will need a source of short wavelength (450 nm or so) UV light. UV light in this range can be found more commonly than you think. We found a battery operated source inside a Travel toothbrush bacteria killer. This is made by VIOlight and it is model VIO200. You can mail order one from, e.g Amazon, or check your local Pharmacy. Once you obtain this piece you can remove the screws from the back to expose the light bulb. Avoid looking directly into the light as you shine it onto the Zine plate and viola. You should visually see the discharge.
It is interesting to note that when you have the electroscope positively charge nothing happens. Why?
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