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What's Your EQ?
May 1966 Radio-Electronics

May 1966 Radio-Electronics

May 1966 Radio-Electronics Cover - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Electronics, published 1930-1988. All copyrights hereby acknowledged.

"What's Your EQ?, May 1966 Radio-Electronics - RF CafeConducted by E. D. Clark

Three puzzlers for the student, theoretician and practical man. Simple? Double-check your answers before you say you've solved them. If you have an interesting or unusual puzzle (with an answer) send it to us. We will pay $10 for each one accepted. We're especially interested in service stinkers or engineering stumpers on actual electronic equipment. We get so many letters we can't answer individual ones, but we'll print the more interesting solutions-ones the original authors never thought of.

Write EQ Editor, Radio-Electronics, 154 West 14th Street, New York, N. Y. 10011.

Answers to this month1s puzzles are on page 89.

Black-Box Equivalent

Can you develop an equivalent circuit for the contents of the box in the diagram? The procedure is to connect a variable voltage source across the input terminals and note the resultant current readings in the reference direction shown. The following results were obtained: When E = 12V, 1= 2A; E = 6V, I = 0; E = 0V, I = 2A.

What's the equivalent circuit of the black box? -Phillip Cutler

Capacitor Puzzler

In the diagram, C1 (1 μF) is initially charged to 2 volts with the polarity shown. The switch is now closed at t = 0. Can you determine the final voltages across the two capacitors and their polarities? -S. G. Joshi

3-Way Switching?

The No. 222 (2.5-volt) flashlight bulb mounted on this black box may be switched on or off by either spst switch (usually three wires and three-way spdt switches would be used). There is a battery in the box. What else? No tubes, relays or semiconductors are involved. -Albert S. Lombard

Quizzes from vintage electronics magazines such as Popular Electronics, Electronics-World, QST, Radio-Electronics, and Radio News were published over the years - some really simple and others not so simple. Robert P. Balin created most of the quizzes for Popular Electronics. This is a listing of all I have posted thus far.

RF Cafe Quizzes

Vintage Electronics Magazine Quizzes

Vintage Electronics Magazine Quizzes

Vintage Electronics Magazine Quizzes

What's Your EQ? Solutions

These are the answers. Puzzles are on page 48.

Black-Box Equivalent

An equivalent circuit can be developed by noting the open-circuit voltage (when I = 0) and short-circuit current (when E = 0). The open-circuit voltage tells us if there is any voltage source within the box. Since an external 6 volts was required for I = 0, it follows there must be a 6-volt bucking source inside.

The current that flows through a short circuit across the output terminals (E = 0) is determined solely by the internal voltage and internal impedance.

The diagram shows the equivalent circuit of the black box.

Capacitor Puzzler

We can replace the charged capacitor C1 with its equivalent-a 2-volt source in series with an uncharged 1-μF capacitor. The diagram shows the final-state conditions after the switch is closed.

The two voltages add to an effective 4 volts. Since C1 = C2, this voltage divides equally between the two capacitors. The final voltage across C2 is 2 volts with upper plate positive. The final voltage across C1 (or its equivalent) is zero (2V - 2V = OV).

3-Way Switching?

The box contains, in addition to the battery, two 5-ohm resistors or equivalent. I used a 10-ohm wirewound adjustable resistor with the slide in the center connected to battery.

If either switch is on when the other is off, the bulb will light. If both switches are on or both off, the bulb does not light. This is a variation of the Wheatstone bridge.

 
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RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a lady's voice announced "You've Got Mail" when a new message arrived...

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