April 1960 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.
Here is a nifty little exercise that appeared in the April 1960 edition of Popular Electronics. It has 10 different light bulb circuits and challenges you to figure out which bulb would burn the brightest. All are intuitively obvious to most of us who have been in the field for decades, but do you remember how to do a circuit mesh analysis to prove your "gut?" One way to help figure out what is going on is to re-draw the circuit to eliminate crossing lines, if possible, as in circuit numbers 2, 4, 6, and 10. Also try drawing electrically common nodes as a single connection point, as in circuit #2 where the two nodes in the upper left and right corners are actually the same point. Finally, try to re-arrange the circuit branches into obvious parallel and series paths to make clear any interdependencies and independencies.
See answers at bottom of page.
Popular Electronics published many quizzes over the years
- some really simple and others not so simple. Robert Balin created many of the quizzes.
This is a listing of all I have posted thus far.
- 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, August
- TV Trouble Quiz,
- Electronics History Quiz,
- Scope-Trace Quiz,
Circuit Analogy Quiz, April 1973
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, June 1963
- Diode Quiz,
- Electronic Curves Quiz, February 1963
- Electronic Numbers Quiz, December 1962
- Energy Conversion Quiz, April 1963
Function Quiz, June 1962
Quiz - February 1967
- Unknown Frequency
Quiz - September 1965
Metals Quiz - October 1964
Measurement Quiz - August 1967
- Meter-Reading Quiz,
Geometry Quiz, January 1965
Factor Quiz, November 1966
Math Quiz, November 1965
- Series Circuit Quiz,
Quiz, March 1966
- Electronic Analogy
Quiz, November 1961
Coupling Quiz, August 1973
- Electronics Analogy Quiz, August 1960
- Audio Quiz,
Unit Quiz, May 1962
Capacitor Circuit Quiz, June 1968
- Quiz on AC Circuit Theory, December 1970
- Magnetic Phenomena Quiz, February 1962
- Electronics Geography Quiz, April 1970
Electronic Menu Quiz, August 1963
- Electronic Noise Quiz, August 1962
- Electronic Current Quiz, October 1963
- Electronic Inventors Quiz, November 1963
Function Quiz, January 1962
- Electronic Measurement Quiz, January 1963
Tube Quiz, February 1961
- Kool-Keeping Kwiz, June
- Find the
Brightest Bulb Quiz, April 1960
ANSWERS: (explanations by Kirt Blattenberger)
When analyzing the circuits, note that for many of the branches one side of the bulb returns directly to the battery, even though at first look it might appear to share with another branch. In circuit 3, for example, you can redraw the circuit connecting the left sides of bulbs A and D directly to the positive battery terminal (anode). Similarly, the right sides of bulbs B and D and the bottom of bulb C directly to the negative battery terminal (cathode).
Bulb C is the only one that has the full battery voltage across it. Bulbs A, B, and D are shorted across their terminals and thus have no voltage across them.
Bulb C is the only one that has the full battery voltage across it. Bulbs A and B share the battery voltage with bulb D.
Bulb D is the only one that has the full battery voltage across it. Bulbs B and C share the battery voltage with bulb A.
Bulb A is the only one that has the full battery voltage across it. Bulbs B and C are shorted across its terminals and therefore have zero volts across them.
This one is a bit tricky, as with circuit #5. Bulbs A and B are in series and therefore share the battery voltage equally Bulb A is in series with the parallel combination of bulbs D and E. The intent of the author is likely that you treat the bulbs as resistors and therefore the parallel combination of bulbs D and E result in half the total resistance of a single bulb. Therefore, the voltage across those two bulbs would be Vbatt * (0.5Rbulb / 1.5Rbulb) = 1/3*Rbulb, and the voltage across bulb B would be 2/3Rbulb. For standard incandescent bulbs, the operational resistance is dependent on the voltage across the bulb, so the voltage division would not be as clean-cut as that, but still bulb A would be brighter. If the bulbs were neon types that maintain a fairly constant voltage across their terminals and regulate current to maintain the voltage, then provided the battery voltage is high enough, all three bulbs would burn with equal brightness.
This is essentially the same circuit as #4.
Bulb E is the only one that has the full battery voltage across it. Bulb B's terminals are shorted and thus 0 volts across it. Bulbs A and C share the battery voltage with Bulb D.
This one is a bit tricky, as with circuit #5. Bulb B is shorted so it plays no role. Bulb A is in series with the parallel combination of bulbs C and D. The intent of the author is likely that you treat the bulbs as resistors and therefore the parallel combination of bulbs C and D result in half the total resistance of a single bulb. Therefore, the voltage across those two bulbs would be Vbatt * (0.5Rbulb / 1.5Rbulb) = 1/3*Rbulb, and the voltage across bulb A would be 2/3Rbulb.
Bulb C is the only one that has the full battery voltage across it. Bulbs A and B are in series with each other and therefore share the battery voltage. The same goes for bulbs D and E.
A quick mesh analysis, assuming the resistive model for the bulbs, shows that the current flowing through bulb E is one unit of current while the current flowing through the other bulbs is 1/2 unit of current. That means bulb E would be the brightest.
Posted August 2, 2019 (original 7/4/2012)