Deck 8: Introduction to Alternating Current and Voltage

Question 1

An ac current is inversely proportional to an ac voltage.

Answer 1

False

Question 2

Commercial line voltages are usually square waves at a frequency of 60 Hz.

Answer 2

False

Question 3

Rise time, fall time, and duty cycle are all terms associated with sine wave measurement.

Answer 3

False

Question 4

One complete sine wave contains 360°.

Question 5

Which of the following can be measured from points B to F in Figure 8 -1?

A)the angle
B)the peak -to -peak voltage
C)the frequency
D)the period

Question 6

The term RMS stands for "root -mean -square."

Question 7

Kirchhoff's voltage law can be used with resistive ac circuits.

Question 8

A sine wave's peak value is smaller than its RMS value.

Question 9

Only frequency increases with the speed of an AC generator.

Question 10

7.07 VPP is approximately equal to 2.5 VRMS.

Question 11

Current flows both ways simultaneously in an AC circuit.

Question 12

Which one of the following represents the value at point G in Figure 8 -1?

A)the peak voltage
B)the RMS voltage
C)the frequency
D)the period

Question 13

What is the instantaneous voltage at 42° on a 230 VP sine wave?

A)149 V
B)154 V
C)115 V
D)76.1 V

Question 14

20 Vrms of alternating current will illuminate a given lamp at the same intensity as 20 V of direct current.

Question 15

The period of a 5 Hz wave form is 200 ms.

Question 16

A sine wave's frequency equals the reciprocal of its period.

Question 17

The higher a sine wave's frequency, the shorter its period.

Question 18

Single -phase power cannot be converted to three -phase power.

Question 19

RMS is another name for peak.

Question 20

The RMS value of a sine wave means .

A)the root mean square value
B)the heating effect of an ac generator of the same voltage
C)the same as IPP × R
D)the same as IP × R

Question 21

If you measure about 56 VPP across the source in Figure 8 -2, what is the trouble?

A)Both R1 and R2 are open.
B)R2 is open.
C)R1 is open.
D)There is no trouble. 56 VPP is a normal measurement for the source voltage.
E)any of these

Question 22

Find RT in Figure 8 -2.

A)4.7 kΩ
B)4.77 kΩ
C)1.13 kΩ
D)6.2 kΩ

Question 23

If a rectangular wave's pulse width is 50 µS and its frequency is 4 kHz, its duty cycle is _.

A)20%
B)1.25%
C)98.75%
D)80%

Question 24

If R1 shorts in Figure 8 -2, VR2 .

A)decreases
B)increases
C)remains the same

Question 25

Calculate the total power dissipation in the circuit in Figure 8 -2.

A)45.6 mW
B)64.5 mW
C)9.12 mW
D)182 mW

Question 26

Calculate VR2 in Figure 8 -2. Figure 8 -2

A)4.84 VP
B)13.15 VP
C)6.84 VPP
D)6.84 VP

Question 27

In Figure 8 -2, what is the instantaneous voltage across R1 at an angle of 22°?

A)12.0 V
B)20.3 V
C)8.03 V
D)2.56 V

Question 28

In Figure 8 -1, which of the following can be measured from point E to point F?

A)the RMS voltage
B)the peak to peak voltage
C)one cycle of voltage
D)the peak voltage

Question 29

In Figure 8 -1, the time from point C to E is called .

A)the period
B)peak voltage
C)a cycle
D)a half -cycle

Question 30

The time required by a 10 V square wave to change from 1 V to 9 V is known as the .

A)rise time
B)pulse width
C)period
D)fall time

Question 31

VR2 if R1 opens in Figure 8 -2.

A)remains the same
B)increases
C)decreases

Question 32

Which point in Figure 8 -1 is 180° away from point E?

A)A
B)B
C)C
D)D

Question 33

Find PR1 in Figure 8 -2.

A)0 W
B)48.9 mW
C)196 mW
D)97.8 mW

Question 34

In Figure 8 -2, what is the instantaneous voltage across R1 at 122°?

A)18.2 V
B)11.2 V
C)5.8 V
D)11.6 V

Question 35

In Figure 8 -1, if the time from point A to H is 60 µs the frequency is .

A)16.7 kHz
B)50 kHz
C)25 kHz
D)More information is required to calculate the frequency.

Question 36

Calculate VR1 in Figure 8 -2.

A)21.4 VP
B)6.84 VP
C)13.7 VP
D)13.2 VP

Question 37

What is the instantaneous voltage at 284° on a 22 VPP sine wave?

A)0.33 V
B)-10.7 V
C)-2.66 V
D)10.7 V

Question 38

Calculate IT in Figure 8 -2.

A)4.55 mAPP
B)9.12 mAPP
C)3.22 mAPP
D)6.44 mAPP

Question 39

What is the approximate peak input voltage to the circuit in Figure 8 -2?

A)20 VP
B)14.1 VP
C)28.3 VP
D)10 VP

Question 40

VPP is measured between points in Figure 8 -1.

A)G and I
B)C and H
C)D and F
D)A and B

Question 41

A 12 VP sine wave equals _ _.

A)8.48 VRMS
B)7.64 VAVG
C)24 VPP
D)all of these

Question 42

A square wave is a unique form of the rectangular pulse wave in that:

A)the duty cycle is 50%.
B)the positive and negative halves are equal.
C)the wave is symmetrical.
D)all of these

Question 43

An oscilloscope's seconds/division switch is set on 20 ms/div. If a sine wave measures 4 divisions horizontally, what frequency is being measured?

A)12.5 Hz
B)50 Hz
C)25 Hz
D)More information is needed.

Question 44

The average value of a rectangular pulse wave is calculated as:

A)Vavg = Vbaseline + (duty cycle)× Vp.
B)Vavg = Vbaseline + Vp.
C)Vavg = 1.57 Vp.
D)Vavg = 0.637 Vp.

Question 45

If the period of a square wave is 22 ms, what is its frequency?

A)22 kHz
B)45.5 kHz
C)45.5 Hz
D)22 Hz

Question 46

A 10 VP sine wave is equal to _ _.

A)100 VPP
B)20 VPP
C)5 VPP
D)none of the above

Question 47

A 60 Hz sine wave completes cycles every 10 seconds.

A)1/16
B)600
C)10
D)6

Question 48

A sine wave's instantaneous voltage is 0 V at degrees.

A)180
B)0
C)360
D)all of these

Question 49

The AC sine wave varies from zero to its maximum value in accordance with:

A)an algebraic function.
B)a geometric progression.
C)a trigonometric relationship.
D)a mathematical formula.

Question 50

If a 10 kΩ resistor carries 5 mARMS of current, its voltage drop equals .

A)70.7 VRMS
B)5 VRMS
C)50 VRMS
D)7.07 VRMS

Question 51

An oscilloscope's seconds/division switch is set on 20 µs/cm. If the trace is 7.5 cm long, what is the period?

A)0.0015 s
B)1.5 µs
C)5 µs
D)150 µs

Question 52

What is the instantaneous voltage at 17° on a 169 VP sine wave?

A)161 V
B)98.8 V
C)49.4 V
D)80.5 V

Question 53

What is the approximate instantaneous voltage at 37° on a 169 VP sine wave?

A)135 V
B)102 V
C)119 V
D)239 V

Question 54

In a two -resistor series circuit VR1 = 6.5 VRMS and VR2 = 3.2 VRMS. The source voltage is .

A)9.19 VP
B)13.7 VP
C)9.7 VP
D)4.53 VP

Question 55

Superimposed DC and AC voltages mean the two voltages are combined:

A)in series -parallel aiding or opposing.
B)in series aiding or opposing.
C)in parallel aiding or opposing.
D)all of these

Question 56

The time (T)and the frequency (f)of an AC waveform are related as:

A)universally proportional.
B)directly proportional.
C)inversely proportional.
D)complimentary proportional.

Question 57

The symbol for the period of a wave form is:

A)W.
B)P.
C)T.
D)F.

Question 58

An oscilloscope's volts/division switch is set on 50 mV/div. If the vertical deflection of the oscilloscope's trace is 1.6 division, what voltage is being measured?

A)1.6 mV
B)80 mV
C)0.008 V
D)50 mV

Question 59

A formula for VRMS is .

A)2 × VP
B)0.707 × VPP
C)0.707 × VP
D)2.8 × VP

Question 60

The period of most AC waveforms is measured in units of:

A)alternations.
B)cycles.
C)seconds.
D)revolutions.

Question 61

The square wave is made up of:

A)just the fundamental frequency.
B)the fundamental frequency and all the odd harmonics.
C)the fundamental frequency and both the odd and even harmonics.
D)the fundamental frequency and all the even harmonics.

Question 62

The largest numerical value in the measurement of alternating current is:

A)peak.
B)rms.
C)average.
D)peak to peak.

Question 63

The output impedance of a function generator is usually

A)600 Ω
B)50 Ω
C)75 Ω
D)any of the above

Question 64

While troubleshooting a circuit the voltage seems to be zero; what if any adjustment should be checked on the oscilloscope?

A)trigger level
B)focus setting
C)time division setting
D)AC/GND/DC switch

Question 65

What type of sensor is used by a clamp meter to measure dc current?

A)transformer action
B)Hall -effect
C)inductive
D)inverter

Question 66

Spectrum analyzers

A)are fquency -domain devices
B)display the sinusoidal components of a waveform
C)are used primarily in RF and microwave applications
D)all of the above

Question 67

The value of a AC sine wave at any instant can be represented by:

A)a graph of the voltage or current vs. the angular measurement.
B)the formula Vi = Vp × sin 0.
C)a phasor whose angle and magnitude are representative of the AC signal.
D)all of these.

Question 68

Iif you want to test a system for its frequency response you would probably employ a(n)

A)arbitrary function generator
B)swept -frequency oscillator
C)multifunction singal generator
D)custom -pattern generator

Question 69

The formula to convert degrees to radians is:

A)
B)
C) $180 ^ { \circ } = \mathrm { n } \text { radians }$
D) $\text { all of these }$

Question 70

Tradionally, radio frequency signal generators operate in the range of

A)100 kHz to 5 GHz
B)100 kHz to 1 GHz
C)500 kHz to 5 GHz
D)10 kHz to 1 GHz

Question 71

This display in Figure 8 -3 illustrates maladjustment of which control on the oscilloscope?

A)volts/div
B)intensity
C)coupling
D)trigger level

Question 72

Troubleshooting an AC circuit can be performed with which of the following tools?

A)digital multimeter
B)analog voltmeter
C)oscilloscope
D)any of the above

Question 73

A signal source that can produce custom waveforms is called a(n)

A)custom -pattern generator
B)multifunction singal generator
C)arbitrary function generator
D)all of the above

Question 74

Superimposing an AC voltage of 3.54 Vrms with a DC source of 10 V results in a waveform that:

A)peaks at 20 V.
B)peaks at 13.54 V.
C)peaks at 15 V.
D)both B and C