Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
This vector circuit matching
quiz will hurt the brain a little more than most of the ones that were printed in Popular
Electronics. In order to score well, it helps to visualize the circuits relative to where
they would appear on a Smith Chart. Capacitive impedances lie in the bottom half and
have negative phases (-s, -jω). Inductance lie in the upper half and have positive
phases (s, jω). The familiar 'ELI
the ICE man' mnemonic helps, too. Be sure to pay attention to the color of the vector
Example: In a purely inductive circuit like #4, voltage leads current by 90°.
Since phase rotation is CCW, you need to look for lettered phase diagram where the white
arrowhead (voltage) is 90° ahead of the black arrow head (current), going in the CCW
direction. Vector diagram later 'H' looks like that. Circuit #10, being purely capacitive,
is just the opposite, so its vector diagram is...? Resistance in parallel or series with
reactance adjusts the phase angle somewhere between 0° and 90°
(not lying on an axis line). The rest are combinations thereof.
Vector-Circuit Matching Quiz
By Robert P. Balin
Vector diagrams are widely used to show the magnitude and phase relationships between
voltages and currents in an a.c. circuit. A knowledge of vectors is a must for understanding
the theory behind frequency modulation and detection, color TV and feedback circuits.
Ten circuits (1-10) are shown below; vector diagrams (A-J) representing the voltages
and currents in the circuits are also shown. To test your knowledge of vectors, match
the diagrams to the circuits. Note that this is a simple matching quiz - obviously special
cases might exist if the effects of resonance were considered. It is also assumed that
all elements are pure (that is, capacitors have only capacitance, inductors only inductance,
and resistors only resistance).
Standard counterclockwise vector rotation is used to indicate angles of lead and lag.
A white arrowhead represents a voltage vector; a black arrowhead
is a current vector. In all cases, the reference is the line along the horizontal, extending
to the right. Relative vectors are shown for all voltages and currents in each circuit.
See answers below.
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.
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
- 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,
Electrochemistry 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
Vector-Circuit Quiz Answers
1-B In a series circuit containing only resistance, the current is in phase with the
2-F In a parallel circuit, there are three currents and a single voltage, which is
used as the reference vector (directed horizontally to the right). The current in an
inductor lags the voltage across the inductor by 90 degrees. The current into a capacitor
leads the voltage across the capacitor by 90 degrees. The total circuit current is the
difference between the branch currents.
3-J The current is used as the reference vector. The voltage drops across the capacitor
and resistor add vectorially to equal the applied voltage.
4-H The applied voltage is the reference vector. The current in the circuit lags the
voltage by 90 degrees.
5-G The applied voltage is the reference vector. The two branch currents add vectorially
to equal the circuit current.
6-A The current is used as the reference vector. The voltage drops across the resistor
and inductor add vectorially to equal the applied voltage.
7-I The current is the reference vector. The voltage drops across the inductor and
capacitor are 180 degrees out of phase, and the difference between them is equal to the
8-E The applied voltage is the reference. The leading currents in each branch are
in phase and add to equal total circuit current.
9-D The applied voltage is the reference. The two branch currents add vectorially
to equal total circuit current.
10-C The applied voltage is the reference. The current in the inductor leads the applied
voltage by 90 degrees.
Posted June 4, 2014