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CapaciQuiz Quiz
August 1961 Popular Electronics

August 1961 Popular Electronics

August 1961 Popular Electronics Cover - RF CafeTable of Contents

Wax nostalgic about and learn from the history of early electronics. See articles from Popular Electronics, published October 1954 - April 1985. All copyrights are hereby acknowledged.

Robert Balin, Popular Electronics magazine's quizmeister, created this CapaciQuiz for the February 1961 issue. Most of these are elementary, but think carefully about the exact wording of Q4 before you answer. With Q8, believe the better explanation is that for a purely capacitive circuit, current and voltage are 90° out of phase, so when the sinewave voltage is at zero, the current is at a maximum. Note that Q6 and Q10 are opposites (parallel vs. series capacitor combinations), so if you have trouble reasoning one of the configurations, work on the other and then you'll know both. Bon chance!

CapaciQuiz Quiz

CapaciQuiz, August 1961 Popular Electronics - RF CafeBy Robert P. Balin

No one can really understand electronics what factors determine capacitance and really works. How many of the questions illustrated below can you answer correctly?

CapaciQuiz (Q1-Q5), August 1961 Popular Electronics - RF Cafe

1)   When charged, the smallest of the two capacitors shown at left will have the largest voltage across it.

TRUE         FALSE

2)   The tuning capacitor will be wide open when you tune in a radio station on the low end of the band.

TRUE         FALSE

3)   The total capacitance of the two capacitors in series is always less than that of the smallest one.

TRUE         FALSE

4)   The lamp in this circuit will light because the capacitor can pass a.c. current.

TRUE         FALSE

5)   A small capacitor cannot be charged to as high a voltage as a large capacitor.

TRUE         FALSE

CapaciQuiz (Q6-Q10), August 1961 Popular Electronics - RF Cafe

6)   Because it is connected in parallel with the main tuning capacitor, a trimmer has its greatest effect at the high end of the band.

TRUE         FALSE

7)   Tightening the adjusting screw on a compression-type capacitor will decrease its capacitance.

TRUE         FALSE

8)   The current (I) into the capacitor is at its maximum when the sine-wave voltage (E) is practically zero.

TRUE         FALSE

9)   Because it is in series with the main tuning capacitor, a padder has its greatest effect at the low end of the band.

TRUE         FALSE

10)   The voltage (E) across the capacitor increases as the frequency of the source voltage is increased.

TRUE         FALSE


See answers below.

Quizzes from vintage electronics magazines such as Popular Electronics, Electronics-World, QST, 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


Vacuum Tube Quiz Answers


1) True. The voltage to which a capacitor is charged depends upon the density of the electrons on one of its plates. A given number of electrons on a small plate will result in a higher charge density and therefore a higher voltage than the same number of electrons on a larger plate.

2) False. When a tuning capacitor is wide open, there is a minimum of plate area in use and the effective capacitance is therefore at a minimum. The smaller the capacitance in parallel with a given inductance, the higher will be the resonant frequency of the circuit.

3) True. Capacitance varies inversely - but not linearly - with the distance between plates. Putting capacitors with different -sized plates in series not only increases the separation between the outermost plates but also reduces the effective plate area to that of the smallest one.

4) False. The plates of a capacitor are separated by a dielectric material which, being an insulator, prevents the capacitor from passing either a,c, or d.c. current. But the movement of electrons on and off the plates is an effective a.c. current to the lamp, and the lamp lights accordingly.

5) False. A capacitor can be charged to any voltage that does not exceed the breakdown voltage of the dielectric material between its plates. The type of dielectric and its thickness determine the working voltage of a capacitor.

6) True. As the capacitance of a trimmer is small in comparison with that of the main tuning capacitor, during most of the latter's tunable range the trimmer will add little to the total capacitance in use. But at the high end of the band where the main tuning capacitance is at a minimum, the trimmer contributes a larger percentage of the capacity in use.

7) False. Tightening the adjusting screw presses the mica dielectric and metal plates closer together. The thickness of the air dielectric which is also present is thus reduced and the capacitance is thereby increased.

8) True. Even when the voltage present is little more than zero a large current flows as the capacitor is being charged. At any later time, the voltage built up on the capacitor limits the circuit current to successively smaller values.

9) True. A padder decreases the effective capacitance across the inductance and thus helps in the alignment of an oscillator at the low end of the band. Since it is relatively large, the padder will have increasingly less influence as the capacitance of the main tuning capacitor is decreased.

10) False. As the frequency of the source voltage is increased, there is less time for the electrons to flow on or off the plates. The voltage to which the capacitor can charge therefore decreases.



Posted August 17, 2022

About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

1996 - 2024


Kirt Blattenberger,


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 nice lady's voice announced "You've Got Mail" when a new message arrived...

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