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Transformer Quiz
April 1962 Popular Electronics

April 1962 Popular Electronics

April 1962 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 master quiz maker, created this "Transformer Quiz" for the April 1962 issue. For each of the nine challenges, a statement is made and you determine whether it is true or false. Even though the quiz was created half a century ago, everything in it applies to today's transformers. If the vacuum tube shown in #4 makes you anxious, mentally replace it with a FET and continue; you really do not need a drawing at all to decide. The explanation for #4's answer involves the tube's plate characteristic, but from an impedance standpoint, the fundamental characteristic of the transformer is what determines the frequency response. For that matter, the drawing is not required for most of them. A huge list of other quizzes is at the bottom of the page, and the answers to this quiz are below that. Enjoy.

Transformer Quiz

By Robert P. Balin

Basically, a transformer is an electrical device in which a magnetic field produced by a primary winding is used to induce a voltage in a secondary winding. But there are as many fine points to transformer theory as there are transformer types. The technician and the hobbyist can review transformer theory and test their knowledge by answering the questions below.

Transformer Quiz, April 1962 Popular Electronics - RF Cafe

1 "Tapping down" the primary winding of any transformer increases the output voltage of the secondary winding of the transformer.

True _____         False _____

 

Transformer Quiz, April 1962 Popular Electronics - RF Cafe

4 The gain of a transformer-coupled audio amplifier stage tends to increase at the low frequencies. 

True _____         False _____

 

Transformer Quiz, April 1962 Popular Electronics - RF Cafe

7 A "Faraday screen" is a copper sheet used to reduce inductive coupling between windings.

True _____         False _____

Transformer Quiz, April 1962 Popular Electronics - RF Cafe

2 If a 50-cps transformer is operated at 60 cps, the transformer will overheat. 

True _____         False _____

 

Transformer Quiz, April 1962 Popular Electronics - RF Cafe

5 With two coils wounds in the same direction on a core, as shown above, the voltage across A-A will be the sum of the voltages across each coil. 

True _____         False _____

 

Transformer Quiz, April 1962 Popular Electronics - RF Cafe

8 The windings of r.f. transformer coils are spiraled back and forth to reduce their distributed capacitance.

True _____         False _____

 

Transformer Quiz, April 1962 Popular Electronics - RF Cafe

3 A 1:2 primary -to -secondary turns ratio will make 100 ohms across the secondary look like 25 ohms to the primary winding. 

True _____         False _____

 

Transformer Quiz, April 1962 Popular Electronics - RF Cafe

6 Transformer iron cores are laminated in order to reduce the heat generated by induced "eddy currents." 

True _____         False _____

 

Transformer Quiz, April 1962 Popular Electronics - RF Cafe

9 Power transformers are made with a laminated iron core material having a narrow hysteresis loop characteristic.

True _____         False _____

 

 

 

See answers below.

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

Transformer Quiz Answers

1 TRUE. Decreasing the number of turns used in the primary winding will increase the turns ratio of the windings. Hence, the voltage ratio will be increased.

2 FALSE. As the frequency of the supply voltage is increased, the inductive reactance of the transformer windings increases and less heat due to loss currents is produced by the same amount of input voltage.

3 TRUE. The impedance ratio of a transformer varies directly as the square of the turns ratio and is therefore 1:4, or 25 ohms in this instance.

4 FALSE. The transformer primary winding impedance decreases as the signal frequency is reduced. Since the primary winding is the plate load for the vacuum tube stage, the resulting lowered plate load impedance causes a reduced output.

5 TRUE. Both coils will act as the secondary winding and develop an output voltage which will be the sum of the voltages across each coil. However, the output voltage will be 180° out of phase with the input voltage.

6 TRUE. Eddy currents exist in the iron core due to the alternating magnetic field. Assembling a core made of thin sheets insulated from each other tends to keep these loss cur- rents and the resulting heat to a minimum.

7 FALSE. The Faraday screen is used to prevent the transfer of electrical energy between the windings by capacitive coupling.

8 TRUE. A "universal" winding prevents the adjacent turns in a coil from running parallel to one another. The capacitance between turns is thereby kept to a minimum, and a more uniform coil Q for a wide band of frequencies is obtained.

9 TRUE. The area enclosed by the hysteresis loop is a measure of the electrical energy lost as heat when the atoms of the core material are rearranged because of the cyclical magnetization of the core. Hence, the narrower the sides or the smaller the area within the loop, the less the losses in a core material. Remember, losses can never be completely eliminated.

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Webmaster: Kirt Blattenberger,
   BSEE - KB3UON - AMA92498
   USAF Radar Technician

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

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