is a quick test of your graph reading skills. It appeared in the
April 1967 edition of Popular Electronics. I missed #6 - a temporary
(hopefully) case of cranial rectumitis on my part. Maybe you will
April 1967 Popular Electronics
of Contents] People old and young enjoy waxing nostalgic about
and learning some of the history of early electronics. Popular Electronics
was published from October 1954 through April 1985. All copyrights are hereby
acknowledged. See all articles from
See all articles from
Graph Interpretation Quiz
By Robert P. Balin
Today's front-line electronic technician
must be able to interpret readily the various charts and graphs
devised by engineers to convey important information on the electrical
characteristics of circuits as well as of individual components.
In addition, the technician must be thoroughly familiar with the
origin and composition of a variety of unusual as well as standard
oscillographic waveforms. Test your ability to interpret the graphs
and waveforms shown below (1-10) by selecting the most likely meaning,
(A) or (B), from the two possibilities given in each case.
1. The family of plate characteristic curves for a
triode shows that as the plate voltage is increased the
a.c. plate resistance (A) increases or (B) decreases.
6. Vacuum-tube mutual transconductance curve indicates
that as grid bias is increased mutual transconductance,
Gm, (A) increases or (B) decreases.
2. The distortion seen in this square-wave test signal
indicates that the amplifier being tested is attenuating
the (A) low frequencies or (B) high frequencies.
7. Of the two load lines, (A) and (B), shown in the
graph at right, which one represents the larger value of
3. The collector current vs. base current curve for
a transistor indicates that as the base current is increased
the beta (gain) of the transistor (A) increases or (B) decreases.
8. The magnetization curve for a transformer core
material shows that as the core goes into saturation its
permeability (A) increases or (B) decreases.
4. This transmitter modulation pattern indicates that
the r.f. carrier is (A) over-modulated or (B) under-modulated
9. The rate of change of a current depicted by a sine
wave is greatest when the current is at its peak (A), or
(B) when it is passing through 0.
5. Output curves show that as a transistor's collector
voltage increases, the a.c. output resistance (A) increases
or (B) decreases.
10. This frequency response curve for a tuned transformer
indicates that the windings are (A) over-coupled or (B)
1 - B The slope
of these curves represents the ratio Ip/Ep,
or conductance (the reciprocal of resistance). As the plate voltage
is increased, the slope and conductance also increase, and the resistance
2 - A The fundamental and low-frequency components
of a square wave contribute chiefly to the center portion of its
flat top. Thus, if an amplifier under test attenuates the low frequencies,
a dip appears in the center of the square-wave test signal.
3 - B The slope of this curve represents the ratio lc/IB,
or beta, the current gain of a transistor. As the base current increases,
the slope of the curve and beta decrease.
4 - A Overmodulation
can reduce an r.f. carrier to zero amplitude during a period of
time as shown by the thin base line through the modulation envelope.
5 - A The slope of this family of curves indicates
changes in the conductance of the transistor. As the collector voltage
(VCE) is increased, the slope and conductance decrease,
and the resistance increases.
6 - B The slope of this curve
represents the ratio Ip/EG, or mutual conductance
(Gm) of this vacuum tube. As the grid voltage (Eg) is
increased, the slope and Gm decrease.
7 - B The slope
of a load line represents the conductance of the load resistance.
The load line with the lesser slope (B) shows a lower conductance,
or higher resistance.
8 - B The slope of this curve reflects
the ratio B/H, the permeability of the core material. As the curve
goes over the knee, the slope and permeability both decrease.
9 - B At its peak amplitude, a sine wave changes from
one finite value to another, but as it passes through zero it changes
from a finite value to zero, resulting in an infinite percent change.
10 - A When the windings of a tuned air-core transformer
are overcoupled, a dip is produced in the center of an otherwise
single-peaked frequency-response curve, and two new resonant peaks
occur at slightly higher and lower frequencies.