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 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.
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 your
By Robert P. Balin
1 - The larger the resistance, the greater the voltage developed
on opening the switch.
2 - Current will continue to flow, even after the supply voltage
has dropped to zero.
3 - Increasing the supply frequency will cause the lamp to glow more
4 - Bunching a number of turns together in a coil will increase its
5 - The inductance of a "swinging" choke decreases as the current
through it increases.
6 - Inserting a brass-tipped tuning wand into a coil will increase
7 - The lamp will glow more brightly as the iron core is moved out
of the coil.
8 - Since a bifilar winding is "doubled back" on itself, it boosts
9 - The tuning slug on an oscillator coil is most withdrawn at the
top end of the band.
See answers below.
Popular Electronics published many quizzes over the
years - 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.
- 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
- Bridge Circuit
Quiz -December 1966
- Diode Function
Quiz - August 1965
- Diagram Quiz,
- 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
- 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
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 zero.
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 inductance.
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 frequency.
Posted May 15, 2014