Brain Teaser Challenge Solution - September 2009 Butch Shadwell
I am a little embarrassed to have put in so many clues, but I still got some incorrect answers. Schlomo “…rolled the wheel down Pearl Street… (The Pearl St. Station was a well known DC generating station.) … It was 1889, and for a ten year old in New York, … (The Pearl St. station burned in 1891.) … he heard his Uncle Lenny describe his new electric light business. As you know, light bulbs were pretty expensive, about a dollar a piece, and they didn’t really last that long. Lenny’s idea was to sell folks lower voltage light bulbs which were a little cheaper and would last a little longer. He planned on buying transformers to reduce the voltage. What turn ratio did he need to run 25 volt bulbs? Hope you remember your electrifying history.”
Edison’s New York power grid ran on 110 volts DC. Of course the use of a transformer to lower the voltage would not have worked without a later invention called a vibrator (used in car radios in order to create the higher B voltage for the vacuum tubes), which would turn DC into pulsing DC which could produce an output from a transformer. But I bet you already knew that.
Brain Teaser Challenge – October 2009 Butch Shadwell
When I got started in this business we used multi-meters with a d’Arsonval meter movement that was powered by the signal that was being measured. Of course the voltage that one read from the meter needle movement could be off a bit depending on the source impedance of the signal. They used to rate the meters input resistance in ohms per volt. Some would be 10,000 ohms/v or even higher sometimes.
If I had a multimeter rated at 1000 ohms per volt, set on the 10 volt range, what voltage would I read from the dial if I measured the voltage at the middle node of a voltage divider composed of two 10,000 ohm resistors in series, across a solid 5 volt DC supply? Later I bought a VTVM or vacuum tube volt meter, with a fixed input resistance of 11 megohms.
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Brain
Teaser Challenge by Butch Shadwell
