Science Buddies: "Ask an Expert"

My son is 11 years old in the 6th grade and found the project of the "Crystal Radio" that he wants to create for his science project. My question is: do you think this is a good project? I was thinking, how would one test it out on the display table......reading the material....it seems that the project needs to be close t\the outdoors if not outdoors completely in order to get a reception......and also.......forgive me if I sound silly......what could the question be for this project......I don't see a problem for this project....the teacher is asking for the problem question.......thanks so much Or maybe im reading this paper wrong......the project could be a problem or it is asking a question. Thanks so much for your reply This project is due February 18, 2011.

nesha10475 - Crystal "sets" are a great way to visit a history long forgotten by the last several generations. I agree that an indoor demonstration may not function well as an efficient antenna and good ground is required. You may be able to demonstrate that by using a cassette recorder to playback a broadcast that you received with a proper antenna/ground connection. As to the merit as a science project, there are a myriad of concepts that could be explained. The whole process of AM radio modulation, transmission, demodulation (the detecting aspect of the semiconductor crystal), frequency tuning (selecting one frequency from many others) all require a little more research, but there is a very thrilling moment when you hear a radio broadcast from a radio you made from very simple parts. To pique your interest a little, here is a link to a crystal radio museum showing over 500 vintage crystal sets made in the first half of the 20th century. When I was your son's age I started to build the first of literally dozens of crystal radios and spent countless hours listening to local stations. Have fun if you decide to go with this project.

There are probably many other crystal set construction plans on the internet. I suggest you do some research and look at alternative construction projects as well as the one you have already seen.

http://www.crystalradio.net/museum/radios/index.shtml

Rick Marz

Excellent advice, Rick.

I would add the following: at the bottom of the Science Buddies Project Idea entitled "Build Your Own Crystal Radio" (https://www.sciencebuddies.org/science- ... p014.shtml), there is a section called VARIATIONS. In this section, several questions are posed, any one of which could form the basis for a good experiment to do with the crystal radio your son builds.

You might also take a peek at the following resource on the Science Buddies website called "Engineering and Programming Project Tips" (https://www.sciencebuddies.org/science- ... ring.shtml). This article compares the scientific method and the engineering design process. Engineering projects presented at science fairs usually define a need rather than ask a question. The 'question' becomes "Can I build a device/system/tool that can solve this need?". This project could be taken in an engineering direction by exploring how to make your radio "better" in some specific way.

Courtney
Science Buddies Staff Member

My daughter is 12 and 6th grade and is also doing a Crystal radio.For those asking whats the problem or question , its whether a crystal can be used to generate electricity. Are there any tips on where to buy the material needed though ?
-Thanksss

Bineny - If I understand your question, you are asking whether a crystal set can be used to generate power. The answer is 'yes' but there are some limitations. Many years ago (circa 1960) crystal radio enthusiasts experimented with adding a transistor to amplify the crystal set audio output. The transistor required a DC power source to work. There were many experimenters that built another crystal detector within the radio and used the rectified DC signal to power the transistor. A storage capacitor was used to accumulate the charge. You could build a crystal set, tune it to a strong AM station, and instead of connecting it to a high impedence headset, connect it to a small capacitor, say 0.22 uF (value not really critical) and using a sensitive voltmeter, measure the DC voltage generated. Use the lowest forward voltage diode as possible, a gold bond germanium diode, for example, for best efficiency. The current generated will be very low, so not too useful for many projects. You might be able to power an old electronic calculator or similar pow power device. The parts for these experiments can usually be purchased at Radio Shack or similar electronic hobby stores. If you have sufficient time, you can purchase over the internet at sites like eBay.

Rick Marz