September 1961 Popular Electronics
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
Have you ever heard
of a "swinging choke?" I surely hadn't, so my probability of getting Inductance
Quiz, which appeared in a 1961 issue of Popular Electronics magazine, question
number 5 correct was 50% at best. I guessed wrong - just my luck. As a result my
score was 8/9 = 89%. Oh, the shame. Maybe you will have a better time of it. Be
careful with Q6 as well. Otherwise, if you understand the fundamentals of inductor
circuit analysis, you will have no problem. Bonne chance.
Inductance, as you may know, is the electrical property frequently compared to mechanical
inertia. To gauge your "inductance" knowledge, solve the problems below, then check
By Robert P. Balin
1 - The larger the resistance, the
greater the voltage developed on opening the switch.
3 - Increasing the supply frequency
will cause the lamp to glow more brightly.
5 - The inductance of a "swinging"
choke decreases as the current through it increases.
7 - The lamp will glow more brightly
as the iron core is moved out of the coil.
9 - The tuning slug on an oscillator
coil is most withdrawn at the top end of the band.
2 - Current will continue to flow,
even after the supply voltage has dropped to zero.
4 - Bunching a number of turns together
in a coil will increase its inductance.
6 - Inserting a brass-tipped tuning
wand into a coil will increase its inductance.
8 - Since a bifilar winding is "doubled
back" on itself, it boosts inductance.
See answers below.
Popular Electronics published many quizzes over the
years (as did a few other magazines to a lesser extent) - some really simple and
others not so simple. Robert P. Balin created many of the quizzes. This
is a listing of all I have posted thus far. Here are my
RF Cafe Quizzes.
Hi-Fi Quiz - October 1955 Radio & Television News
- Electronics Physics
Quiz - March 1974
- A Baffling Quiz
- January 1968
- Electronics IQ
Quiz - May 1967
- Plug and Jack
Quiz - December 1967
Switching Quiz - October 1967
Angle Quiz - September 1967
Electronics Quiz - July 1967
Radio Quiz - April 1950 Radio & Television News
- Bridge Circuit
Quiz -December 1966
- Diode Function
Quiz - August 1965
- Diagram Quiz,
- Quist Quiz - November
- TV Trouble Quiz,
- Electronics History Quiz,
- Scope-Trace Quiz,
Circuit Analogy Quiz, April 1973
Test Your Knowledge of Semiconductors, August 1972
- Ganged Switching
Quiz, April 1972
- Lamp Brightness
Quiz, January 1969
- Lissajous Pattern Quiz, September 1963
Quizoo, October 1962
- Electronic Photo Album Quiz, March 1963
- Electronic Alphabet Quiz, May 1963
- Quiz: Resistive?
Inductive? or Capacitive?, October 1960
- Vector-Circuit Matching Quiz, June 1970
Quiz, September 1961
- RC Circuit Quiz,
- Diode Quiz, July
- Electronic Curves Quiz, February 1963
- Electronic Numbers Quiz, December 1962
- Energy Conversion Quiz, April 1963
- Coil Function
Quiz, June 1962
Co-Inventors Quiz - January 1965 Electronics World
"-Tron" Teasers Quiz - October 1963 Electronics World
- Polarity Quiz
- March 1968
Television I.Q. Quiz - October 1948 Radio & Television News
- Amplifier Quiz
Part I - February 1964
Quiz - February 1967
Frequency Quiz - September 1965
Metals Quiz - October 1964
Measurement Quiz - August 1967
Quiz, June 1966
Geometry Quiz, January 1965
Factor Quiz, November 1966
Math Quiz, November 1965
- Series Circuit
Quiz, May 1966
Quiz, March 1966
Quiz: Test Your Sales Ability - April 1947 Radio News
Analogy Quiz, November 1961
Coupling Quiz, August 1973
- Electronics Analogy Quiz, August 1960
- Audio Quiz, April
- Electronic Unit
Quiz, May 1962
Circuit Quiz, June 1968
- Quiz on AC Circuit Theory, December 1970
- Magnetic Phenomena Quiz, February 1962
- Electronics Geography Quiz, April 1970
Menu Quiz, August 1963
- Electronic Noise Quiz, August 1962
- Electronic Current Quiz, October 1963
- Electronic Inventors Quiz, November 1963
- Resistor Function
Quiz, January 1962
- Electronic Measurement Quiz, January 1963
- Vacuum Tube Quiz,
- Kool-Keeping Kwiz, June
- Find the Brightest
Bulb Quiz, April 1960
1 - True. When the switch is opened, the inductance of the coil
tends to maintain the same value of current flow in the circuit. And the higher
the value of the series resistance, the greater the e.m.f. which will be developed.
2 - True. Since current lags voltage by 90 degrees in a purely
inductive circuit, current will continue to flow after the voltage has dropped to
3 - False. Because of the back e.m.f. induced in the coil as
the current through it changes, the greater the rate of current change, the greater
is the opposition to such change. Thus, the higher the frequency of the current
through the coil, the greater the inductance, and the smaller the voltage delivered
to the lamp.
4 - True. Closely spacing a number of turns in a coil will increase
the strength of its magnetic field and thus its inductance.
5 - True. A swinging choke is an inductor which is designed
to reach a maximum amount of magnetization or "saturation" at low values of rated
current. From this point on, an increase in the amount of current reduces the degree
of magnetization and hence the inductance. A greater portion of the source voltage
therefore becomes available to compensate for the larger resistive voltage drops
occurring within the power supply.
6 - False. Eddy currents induced in the brass will produce a
magnetic field which opposes that of the coil and thus effectively reduces the coil's
7 - True. The iron core serves to increase the coil's inductance,
leaving only a small voltage available to light the lamp. Removing the core therefore
increases the voltage applied to the lamp.
8 - False. The current in this type of coil flows in opposite
directions in adjacent turns. Back e.m.f.'s of self-induction are produced in all
of the turns; but since the back e.m.f.'s of mutual induction will all have the
opposite polarity, they cancel out the back e.m.f.'s of self-induction and thus
make the coil "non-inductive."
9 - True. When the slug is moved out of the coil, the "core"
consists of air, and the inductance of the coil is decreased. Since the smaller
magnetic field is able to expand and contract at a faster rate, the coil is now
able to transfer its electrical energy into the resonating capacitor at a higher
Posted October 6, 2020(original