Please Support RF Cafe by purchasing my  ridiculously low−priced products, all of which I created.

# Potentiometer QuizSeptember 1962 Popular Electronics

 September 1962 Popular Electronics Table 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.

Here is yet another of Robert Balin's many electronics-related quizzes which he created for Popular Electronics magazine (see big list of others at bottom of page). This Potentiometer Quiz showed up in the September 1962 issue. Since the basics of potentiometers have not changed since the first variable resistor was created, it is still a useful challenge for today - and tomorrow. The unique aspect of this quiz is that the potentiometer is connected in series and/or parallel with other fixed resistors in a manner where the output voltage is not necessarily a linear function of where the wiper arm lies along the pot. A DC source (battery) is used, and there are no reactive or nonlinear elements, so that simplifies things considerably. Still, it might take some head scratching to arrive at the correct conclusion for some of them. Assume the output waveform is linear along the abscissa as the potentiometer is adjusted through its resistance range. All resistances have the same value, so assign whatever makes it easiest for you.

Potentiometer Quiz

By Robert P. Balin

When the potentiometer wiper arm is moved from point "1" to point "2" in each of the circuits above (1 through 8), the output voltage, "E," varies as shown by one of the curves below (A through H). See if you can match them up. All resistors and linear potentiometers (some with center taps) are of the same resistance value. The correct answers appear on page 104.

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.

Many experimenters can intuitively come up with the correct answers to this quiz by examining each circuit, visually moving the potentiometer wiper arm, and estimating the output voltage, "E." In a sense, they plot the curves. You can do the same thing either by setting up the circuit on your workbench and measuring the voltage out as the wiper arm is rotated, or by mathematically computing the output voltage.

The computations and plotting of the curve for each problem can be easily done by drawing equivalent circuits for different positions of the potentiometer's wiper arm. In most cases, only five positions are needed. They are for wiper arm settings of zero (at point "1"), 1/4 turn, 1/2 turn, 3/4 turn and a full turn (at point "2"). Remember that all of the resistors and linear potentiometers have equal resistance value, and that a potentiometer set at 1/4 turn will have one-quarter of its resistance between terminal 1 and the wiper arm and the remainder between the wiper arm and terminal 2. Potentiometers with center taps are just like the others except that the center tap permits connection to the mid-point of the potentiometer's resistance, which occurs at 1/2 turn of the wiper arm.

If you have a good sixth sense, or your computations are correct, you will agree with the answers given below.

1-D       3-B       5-F       7-E

2-G       4-C       6-H       8-A

Posted October 5, 2023