Gibilisco - Alternating-current Basics
- 1.Which of the following can vary with ac, but never with dc?
- A.
Power
- B.
Voltage
- C.
Frequency
- D.
Amplitude
- 2.The length of time between a point in one cycle and the same point in the next cycle of an acwave is the
- A.
Frequency.
- B.
Magnitude.
- C.
Period.
- D.
Polarity.
- 3.On a spectrum analyzer, an ac signal having only one frequency component looks like
- A.
A single pip.
- B.
A sine wave.
- C.
A square wave.
- D.
A sawtooth wave.
- 4.The period of an ac wave, in seconds, is
- A.
The same as the frequency in hertz.
- B.
Not related to the frequency in any way.
- C.
Equal to 1 divided by the frequency in hertz.
- D.
Equal to the peak amplitude in volts divided by the frequency in hertz.
- 5.The sixth harmonic of an ac wave whose period is 1.000 millisecond (1.000 ms) has afrequency of
- A.
0.006 Hz.
- B.
167.0 Hz.
- C.
7.000 kHz.
- D.
6.000 kHz.
- 6.A degree of phase represents
- A.
6.28 cycles.
- B.
57.3 cycles.
- C.
1⁄60 of a cycle.
- D.
1⁄360 of a cycle.
- 7.Suppose that two ac waves have the same frequency but differ in phase by exactly 1⁄20 of a cycle. What is the phase difference between these two waves?
- A.
18°
- B.
20°
- C.
36°
- D.
5.73°
- 8.Suppose an ac signal has a frequency of 1770 Hz. What is its angular frequency?
- A.
1770 rad/s
- B.
11,120 rad/s
- C.
282 rad/s
- D.
Impossible to determine from the data given
- 9.A triangular wave exhibits
- A.
An instantaneous rise and a defined decay.
- B.
A defined rise and an instantaneous decay.
- C.
A defined rise and a defined decay, and the two are equal.
- D.
An instantaneous rise and an instantaneous decay.
- 10.Three-phase ac
- A.
Has sawtooth waves that add together in phase.
- B.
Consists of three sine waves in different phases.
- C.
Is a sine wave with exactly three harmonics.
- D.
Is of interest only to physicists.
- 11.If two perfect sine waves have the same frequency and the same amplitude, but are inopposite phase, the composite wave
- A.
Has twice the amplitude of either input wave alone.
- B.
Has half the amplitude of either input wave alone.
- C.
Is complex, but has the same frequency as the originals.
- D.
Has zero amplitude (that is, it does not exist), because the two input waves cancel each other out.
- 12.If two perfect sine waves have the same frequency and the same phase, the composite wave
- A.
Is a sine wave with an amplitude equal to the difference between the amplitudes of the two input waves.
- B.
Is a sine wave with an amplitude equal to the sum of the amplitudes of the two original waves.
- C.
Is not a sine wave, but has the same frequency as the two input waves.
- D.
Has zero amplitude (that is, it does not exist), because the two input waves cancel each other out.
- 13.In a 117-V rms utility circuit, the positive peak voltage is approximately
- A.
+82.7 V.
- B.
+165 V.
- C.
+234 V.
- D.
+331 V
- 14.In a 117-V rms utility circuit, the peak-to-peak voltage is approximately
- A.
82.7 V.
- B.
165 V.
- C.
234 V.
- D.
331 V.
- 15.In a perfect sine wave, the peak-to-peak amplitude is equal to
- A.
Half the peak amplitude.
- B.
The peak amplitude.
- C.
1.414 times the peak amplitude.
- D.
Twice the peak amplitude.
- 16.Which one of the following does not affect the power output available from a particular acgenerator?
- A.
The strength of the magnet
- B.
The number of turns in the coil
- C.
The type of natural energy source used
- D.
The speed of rotation of the coil or magnet
- 17.If a 175-V dc source were connected in series with the utility mains from a standard walloutlet, the result would be
- A.
Smooth dc at a constant voltage.
- B.
Pure ac with equal peak voltages.
- C.
Ac with one peak voltage greater than the other.
- D.
Fluctuating dc.
- 18.An advantage of ac over dc in utility applications is the fact that
- A.
Ac is easier to transform from one voltage to another.
- B.
Ac is transmitted with lower loss in wires.
- C.
Ac can be easily obtained from dc generators.
- D.
Ac can be generated with less-dangerous by-products.
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