Deck 11: Introduction to Alternating Current and Voltage

Question 1

A sine wave reaches its rms value of 70.7% of the peak voltage at an angle of how many radians?

A) 2n rad
B) n rad
C) n/4 rad
D) n/2 rad

Answer 1

n/4 rad

Question 2

A harmonic frequency is always an integral odd or even) multiple of the fundamental frequency.

Answer 2

True

Question 3

A sine wave is the only waveform that contains no harmonics. All other waveforms are composed of a fundamental sine wave and harmonically related sine waves.

Answer 3

True

Question 4

The rate of change of a voltage sine wave is due to the change in flux density.

Question 5

A given rms value of a sine wave is equal to the same value of DC voltage with respect to the heat produced in a resistor.

Question 6

Increasing positive angles of a phasor move clockwise from the reference point.

Question 7

Refer to Figure 11-3. Which of the following statements is correct?

A) Waveform A lags Waveform B
B) Waveform A leads Waveform B.

Question 8

A sawtooth voltage waveform has a linear ramp changing voltage level with respect to time.

Question 9

Given the drawing in Figure 11-2, and the Time-per-division knob is set to 1.0 ms/Div, what is the frequency of Waveform A?

A) 2 kHz
B) 400 Hz
C) 100 Hz
D) 5 kHz

Question 10

A complete sine wave contains:

A) 3n/2 radians
B) n radians
C) n/2 radians
D) 2n radians

Question 11

Refer to Figure 11-3. Waveforms A and B have the same frequency, but appear to have different amplitudes. Is this possible?

A) No
B) Yes

Question 12

Refer to Figure 11-3. The phase shift between Waveform A and Waveform B expressed in Radians is:

A) n/4 rad
B) 2n/6 rad
C) 2n rad
D) n/2 rad

Question 13

Given the drawing in Figure 11-3, the phase shift between Waveform A and Waveform B is:

A) 180°
B) 60°
C) 90°
D) 45°

Question 14

You count 5 divisions on the horizontal axis on the scope. The Time-per-division knob is set to 1.0 ms/Div. Given the drawing in Figure 11-2, what is the frequency of Waveform B?

A) 0.2 kHz
B) 0.5 kHz
C) 1 kHz
D) 5 kHz

Question 15

One radian equals:

A) 90°
B) 57.3°
C) 45°
D) 114.6°

Question 16

Frequency is the reciprocal of the period.

Question 17

The average value of a sine wave is zero.

Question 18

For Waveform A, you count 4 divisions on the Vertical axis on the scope. The Volts-per-division knob is set to 50 mV/Div. Given the drawing in Figure 11-2, what is the Peak-to-peak amplitude of Waveform A?

A) 500 mV
B) 250 mV
C) 0.2 V
D) 50 mV

Question 19

There are 360 degrees in a complete cycle of a sine wave.

Question 20

When the phasor moves in the clockwise direction, the various angle positions are labeled as negative values.

Question 21

Find the frequency of a periodic wave that has a period of one hour.

A) 0.278 mHz
B) 27.8 mHz
C) 2.78 mHz
D) 278 mHz

Question 22

On an oscilloscope display:

A) a flat horizontal trace means voltage is constant.
B) a straight diagonal trace means voltage is changing at a steady rate.
C) all the above
D) voltage is on the vertical axis and time is on the horizontal axis.

Question 23

What angle in degrees is equivalent to n/3 radians?

A) 60°
B) 90°
C) 120°
D) 30°

Question 24

The negative alternation of a sine wave of current indicates that:

A) power in the circuit will be less during this time.
B) the current has changed direction.
C) the current is the opposite direction and polarity across components changes.
D) it is different in amplitude from its positive alternation.

Question 25

The phase difference between sine waves of different frequencies is:

A) the same throughout time
B) constantly changing.
C) the difference in their fixed time displacement
D) equal to their frequency differences.

Question 26

A sine wave reaches half of its peak value at:

A) 90°
B) 30°
C) 60°
D) 45°

Question 27

The frequency of the waveform in Figure 11-4 is:

A) 1 Hz
B) 1 kHz
C) 1000 cycles per second
D) Both B and C are correct.

Question 28

What is the period of a 50 kHz sine wave?

A) 5 × 104 s
B) 5 µs
C) 20 µs
D) 50 µs

Question 29

The equation for finding the frequency, when the period is known is:

A) f = 1/T
B) T = 0.707f
C) T = 1/f
D) T = n/2f)

Question 30

If the effective voltage of an ac receptacle is 120 V, what is the peak-to-peak voltage?

A) 84.8 V
B) 169.7 V
C) 339.4 V
D) 240 V

Question 31

The Period of the waveform in Figure 11-4 is:

A) 0.5 mS
B) 1 kHz
C) 1.0 mS
D) 100 Hz

Question 32

The equation for finding the Period, when the frequency is known is:

A) T = 1/f
B) T = n/2f)
C) T = 0.707f
D) f = 1/T

Question 33

If a sine wave signal measured 100 mV peak-to-peak, how many volts would be read by a voltmeter?

A) 63.7 mV
B) 14.14 mV
C) 70.7 mV
D) 35.4 mV

Question 34

The instantaneous value of a sine wave is:

A) constantly changing
B) 0.707 of its peak value.
C) equivalent to a like DC value
D) equal to 1.414 of the rms value.

Question 35

If the rms value of the waveform in Figure 11-4 is 100 V rms, what is the peak voltage?

A) 70.07 V
B) 288.28 V
C) 200 V
D) 141.4 V

Question 36

The is defined as the time the output is active divided by the total period it could possibly be active.

A) active ratio
B) duty cycle
C) pulse width
D) on time

Question 37

If the rms value of the waveform in Figure 11-4 is 10 V rms, what is the peak voltage?

A) 7.07 V
B) 20 V
C) 28.28 V
D) 14.14 V

Question 38

If the rms value of the waveform in Figure 11-4 is 12 V rms, what is the peak voltage?

A) 16.97 V
B) 8.48 V
C) 33.94 V
D) 15.3 V

Question 39

The coordinate system consists of:

A) four quadrants
B) two perpendicular lines.
C) two axes, x and y
D) all of the above.

Question 40

How much time has elapsed when the waveform in Figure 11-4 reaches its rms value?

A) 0.25 mS
B) 0.707 mS
C) 0.5 mS
D) 0.125 mS

Question 41

Phasor algebra for sinusoidal quantities is applicable only for waveforms which have different frequencies.

Question 42

The length of a phasor is called the magnitude.

Question 43

The length of a phasor represents the amplitude.

Question 44

Determine the instantaneous value of a sine wave whose rms is 20 V, and phase angle is -297 degrees.

A) -17.8 V
B) -25.2 V
C) +17.8 V
D) +25.2 V

Question 45

The length of the phasor "arrow" represents the of a quantity.

A) amplitude
B) frequency
C) angle
D) direction

Question 46

A phasor represents a time-varying quantity in terms of both magnitude and direction.

Question 47

The instantaneous value of a sine wave voltage, at any point, is equal to the vertical distance from the tip of the phasor to the:

A) horizontal axis
B) negative peak
C) positive peak
D) vertical axis

Question 48

The time base control of the oscilloscope does which of the following?

A) adjusts the vertical scale
B) shows you the current time of day
C) sends a clock pulse to the probe
D) sets the amount of time represented by the horizontal width of the screen

Question 49

The equivalent negative angle for a positive angle of 30 degrees is:

A) 330 degrees
B) -330 degrees
C) -60 degrees
D) -150 degrees

Question 50

In a circuit that contains a dc voltage source of 15 V and an ac voltage source of 50 Vp and a resistive load, what would be the maximum and minimum voltage measured across the resistive load?

A) VMAX = zero V, VMIN = 35 V
B) VMAX = 65 V, VMIN = zero V
C) VMAX = 35 V, VMIN = 65 V
D) VMAX = 65 V, VMIN = 35 V

Question 51

Phasors are a convenient graphic way of representing sine wave voltages in terms of their:

A) magnitude and frequency
B) magnitude and amplitude
C) magnitude and period
D) magnitude and phase

Question 52

The angular position of a phasor represents the amplitude of a sine wave.

Question 53

Which of the following expresses angular velocity?

A) 2n/T
B) f/T
C) n/T
D) 2n × T

Question 54

The opposite side of a right triangle is equal to the hypotenuse times the sine of the angle 0.

Question 55

The velocity of rotation is called:

A) the frequency
B) the angular velocity
C) the wavelength
D) the speed

Question 56

What is the angular velocity of a phasor representing a sine wave with a frequency of 1.4 kHz?

A) 440 rad/s
B) 4398 rad/s
C) 8796 rad/s
D) 880 rad/s

Question 57

The length of a phasor is represented by the formula v = Vpsin 0.

Question 58

A four-pole generator has a rotation speed of 400 rps. Determine the frequency of the output voltage.

A) 200 Hz
B) 400 Hz
C) 800 Hz
D) 1600 Hz