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Showing posts from June, 2011

Lecture 24 of MIT Freshman EM

I'm back to studying for the Physics quals at New Mexico State. Today I reviewed lecture 24 of the Freshman EM class there. You can watch it below. Timestamps and additional notes follow.

At the end of the video, there's a very cool explanation and demonstration of a Ruhmkorff, (shown at left). It works in a similar manner to a car's induction coil and can make sparks in air between terminals separated by 10 cm. To read more about it, check out the Wikipedia article on indicution coils.

Timestamps and notes
RC circuit charging over time

7:00 derivation of differential equation for RC circuit.

8:34 Solution

21:48 Transformers
33:00 Cool transformer demo
39:00 Induction heater demo with a nail
43:00 car transformer
49:00 Rumkorf spark generator

Mecanno Magazine Archive

Check out this great resource of scientific and engineering articles written for kids between 1916 and 1981! The covers are fascinating! They were printed by the manufacturers of the Mechanno building sets, which are known as Erector sets here in the States. Each issue contains articles about interesting technologies of the time and the future of technology as the authors saw it then.

The early motto of the magazine is my favorite:
"To Help Meccano Boys to Have More Fun Than Other Boys"

SDR Construction Notes from Jeri Ellsworth

Jeri Ellsworth posted an interesting video on youtube outlining her software defined radio construction. This is a pretty slick example of what can be done with SDR.

Television Inventor Worked on Fusion

While plunking around Wikipedia this morning, I came across an article on Wikipedia about Philo T. Farnsworth, one of the inventors of the television system. It turns out he also invented a table-top fusion device. It never took off as a power source, but the basis of the invention serves as a commercially available table-top neutron source. For more details, see the link below:

Scoring fixes to embeddable free ham radio practice tests

Several scoring bugs and one multiple test bug were fixed on the embeddable google gadget free ham radio practice exams today. The scoring bugs fixed should make for reliable tracking of your unanswered and unpassed exam questions. There was also an issue where taking a test a second time didn't always work correctly. That's fixed now. Finally, if you were having trouble using the tests with IE8, they're up and running! If you run into new or the same issues, please let me know at and I'll get it fixed.

Have fun!

73 de KD0FNR Hamilton

Extra Class Rectangular Impedance Video Help... by Pirates

There's a new video help topic available for the free ham radio practice exams at: Feedback is welcome!

Study the Correct General Pool

If you're taking the general class test after on or after July 1st of 2011, be sure to not use the google gadget practice exam and do use the practice exams at:

Your same user account will work on either practice exam, but the exam set at Copasetic Flows has the new general question pool as well as the current one. Just select the 'NEW General' tab on the practice exams. The question pool on the google gadget will change over to the new one on July 11th.