1.
Alternating current can be defined as
current that varies in
Correct Answer
A. Amplitude and direction
Explanation
Alternating current refers to the flow of electric charge that constantly changes its direction and amplitude. In other words, the current reverses its flow periodically, moving back and forth in a circuit. The amplitude of the current refers to its maximum value, while the direction indicates the flow of the current. Therefore, the correct answer is "amplitude and direction."
2.
Before a 120-volt dc source can be used
to power a 12-volt load, the voltage
must be reduced. Which of the
following methods can be used?
Correct Answer
B. A resistor placed in series with the load
Explanation
A resistor placed in series with the load can be used to reduce the voltage in a 120-volt dc source to power a 12-volt load. When resistors are connected in series, the total resistance increases, causing a voltage drop across the resistor. This voltage drop can be used to reduce the voltage supplied to the load. Therefore, by placing a resistor in series with the load, the voltage can be effectively reduced to the desired level.
3.
Alternating current has replaced direct
current in modern transmission systems
because it has which of the following
advantages?
Correct Answer
D. Ac can be readily stepped up or down
Explanation
Alternating current (AC) can be readily stepped up or down, meaning it can be easily transformed to higher or lower voltage levels. This is one of the main advantages of AC over direct current (DC) in modern transmission systems. By stepping up the voltage, AC can be transmitted over long distances with minimal line loss. Additionally, AC can be transmitted at higher current levels, which allows for more efficient power transmission. Therefore, the ability to easily step up or down the voltage makes AC the preferred choice for modern transmission systems.
4.
A waveform is a graphic plot of what
quantities?
Correct Answer
B. Amplitude versus time
Explanation
A waveform is a graphic plot that represents the variation of a quantity over time. In this case, the correct answer is "Amplitude versus time" because a waveform typically shows the change in amplitude (strength or intensity) of a signal or wave over a specific period of time. It is a graphical representation of how the amplitude of a signal varies as time progresses.
5.
Which of the following properties
surrounds a current-carrying conductor?
Correct Answer
A. A magnetic field
Explanation
A current-carrying conductor creates a magnetic field around it. This is due to the movement of the charges (electrons) within the conductor. The magnetic field is generated in a circular pattern, with the strength of the field increasing as the current increases. This magnetic field can interact with other magnetic fields or magnetic materials, leading to various phenomena such as attraction, repulsion, and induction. Therefore, the correct answer is A magnetic field.
6.
Which of the following statements
accurately describes the magnetic field
surrounding a current-carrying
conductor?
Correct Answer
C. It is perpendicular to and equal along all parts of the conductor
Explanation
The magnetic field surrounding a current-carrying conductor is perpendicular to the conductor and equal along all parts of the conductor.
7.
Which of the following factors
determine(s) the intensity of a magnetic
field surrounding a coil?
Correct Answer
D. All of the above
Explanation
The intensity of a magnetic field surrounding a coil is determined by multiple factors. The amount of current flow through the coil plays a significant role in determining the intensity of the magnetic field. Additionally, the type of core material used in the coil can also affect the intensity of the magnetic field. Finally, the number of turns in the conductor, or the coil, can also influence the intensity of the magnetic field. Therefore, all of the factors mentioned - the amount of current flow, the type of core material, and the number of turns in the conductor - contribute to determining the intensity of the magnetic field surrounding a coil.
8.
When you grasp a coil in your left hand
with your thumb pointing in the
direction of the north pole, your fingers
will be wrapped around the coil in the
direction of the
Correct Answer
C. Current flow
Explanation
When you grasp a coil in your left hand with your thumb pointing in the direction of the north pole, your fingers will be wrapped around the coil in the direction of the current flow. This is known as the right-hand grip rule, where the thumb represents the direction of the current and the curled fingers indicate the direction of the magnetic field created by the current flow.
9.
The power consumed in a conductor in
realigning the atoms which set up the
magnetic field is known as what type of
loss?
Correct Answer
A. Hysteresis loss
Explanation
Hysteresis loss refers to the power consumed in a conductor when the atoms within the conductor are realigned to set up the magnetic field. This loss occurs due to the lagging of the magnetic field behind the magnetizing force, resulting in energy dissipation in the form of heat. Therefore, hysteresis loss is the correct term to describe this type of power loss.
10.
The magnetic field surrounding a
straight conductor is (a) what shape, and
(b) is in what position relative to the
conductor?
Correct Answer
D. (a) Concentric circles (b) Perpendicular
Explanation
The correct answer is (a) Concentric circles (b) Perpendicular. When a current flows through a straight conductor, the magnetic field that is generated around it takes the shape of concentric circles. These circles are centered around the conductor and are perpendicular to it.
11.
Why is a two-pole magnetic field set up
around a coil?
Correct Answer
A. Because separate lines of magnetic force link and combine their effects
Explanation
A two-pole magnetic field is set up around a coil because separate lines of magnetic force link and combine their effects. This means that the magnetic field lines originating from the two poles of the coil come together and interact, resulting in a stronger and more concentrated magnetic field. This phenomenon is important in various applications, such as in electromagnets, transformers, and electric motors, where the strength and direction of the magnetic field are crucial for their proper functioning.
12.
When a conductor is moving parallel to
magnetic lines of force, (a) what relative
number of magnetic lines are cut, and
(b) what relative value of emf is
induced?
Correct Answer
B. (a) Minimum, (b) minimum
Explanation
When a conductor is moving parallel to magnetic lines of force, the relative number of magnetic lines that are cut is minimum. This is because the conductor is moving parallel to the lines of force, so it is not intersecting many of them. As a result, the induced emf is also minimum. This is because the emf is directly proportional to the rate at which magnetic lines are cut by the conductor. Since the conductor is cutting a minimum number of lines, the induced emf is also minimum.
13.
When the induced voltage in a
conductor rotating in a magnetic field is
plotted against the degrees of rotation,
the plot will take what shape?
Correct Answer
B. A sine curve
Explanation
When the induced voltage in a conductor rotating in a magnetic field is plotted against the degrees of rotation, the plot will take the shape of a sine curve. This is because the induced voltage is directly proportional to the rate of change of magnetic flux, which follows a sinusoidal pattern as the conductor rotates. As the conductor moves through the magnetic field, the flux through the conductor changes, resulting in a varying induced voltage that follows the shape of a sine curve.
14.
When a loop of wire is rotated through
360º in a magnetic field, the induced
voltage will be zero at which of the
following points?
Correct Answer
C. 180º
Explanation
When a loop of wire is rotated through 360º in a magnetic field, the induced voltage will be zero at 180º. This is because at this point, the orientation of the loop is perpendicular to the magnetic field lines, resulting in no change in flux and hence no induced voltage.
15.
When a loop of wire is rotated 360º in a
magnetic field, at what points will the
induced voltage reach its maximum (a)
positive, and (b) negative values?
Correct Answer
D. (a) 90º , (b) 270º
Explanation
When a loop of wire is rotated 360º in a magnetic field, the induced voltage reaches its maximum at two specific points. At 90º, the induced voltage reaches its maximum positive value. This is because at this point, the maximum number of magnetic field lines are passing through the loop, resulting in a higher induced voltage. On the other hand, at 270º, the induced voltage reaches its maximum negative value. This is because at this point, the maximum number of magnetic field lines are passing through the loop in the opposite direction, resulting in a negative induced voltage.
16.
When a coil of wire makes eight
complete revolutions through a single
magnetic field, (a) what total number of
alternations of voltage will be generated
and, (b) what total number of cycles of
ac will be generated?
Correct Answer
B. (a) 16, (b) 8
Explanation
When a coil of wire makes eight complete revolutions through a single magnetic field, it will generate a total of 16 alternations of voltage. Each revolution of the coil corresponds to two alternations of voltage (one positive and one negative), so eight revolutions will result in 16 alternations.
Similarly, the total number of cycles of AC generated will be 8. Each alternation of voltage corresponds to one cycle of AC, so the 16 alternations will result in 8 cycles of AC.
17.
According to the left-hand rule for
generators, when your thumb points in
the direction of rotation, your (a)
forefinger and (b) your middle finger
will indicate the relative directions of
what quantities?
Correct Answer
D. (a) Magnetic flux, north to south, (b) Current
Explanation
According to the left-hand rule for generators, when your thumb points in the direction of rotation, your forefinger indicates the direction of the magnetic field (magnetic flux) and your middle finger indicates the direction of the current. Therefore, the correct answer is (a) Magnetic flux, north to south, (b) Current.
18.
Continuous rotation of a conductor
through magnetic lines of force will
produce what type of (a) voltage and
(b) waveform?
Correct Answer
A. (a) Ac, (b) sine wave
Explanation
When a conductor continuously rotates through magnetic lines of force, it will produce an alternating current (AC) voltage. AC voltage periodically changes in magnitude and direction. The waveform produced in this case will be a sine wave. A sine wave is a smooth, continuous waveform that oscillates between positive and negative values, representing the alternating current.
19.
What is the term for the number of
complete cycles of ac produced in one
second?
Correct Answer
C. Frequency
Explanation
Frequency is the term used to describe the number of complete cycles of alternating current (ac) produced in one second. It is a measure of how many times a wave oscillates or completes a cycle per second. In the context of ac, frequency is measured in hertz (Hz) and determines the rate at which the current alternates direction.
20.
What is the unit of measurement for
frequency?
Correct Answer
B. Hertz
Explanation
The correct answer is Hertz. Hertz is the unit of measurement for frequency. It represents the number of cycles or oscillations per second in a wave or signal. It is commonly used to measure the frequency of sound waves, radio waves, and electrical signals.
21.
A loop of wire rotating at 60 rpm in a
magnetic field will produce an ac
voltage of what frequency?
Correct Answer
A. 1 Hz
Explanation
The ac voltage produced by a loop of wire rotating in a magnetic field is determined by the frequency of rotation. In this case, the loop is rotating at 60 rpm (revolutions per minute). To convert this to Hz (Hertz), we need to divide by 60 (since there are 60 seconds in a minute) to get the number of rotations per second. Therefore, the frequency of the ac voltage produced by the loop is 1 Hz.
22.
An ac voltage of 250 hertz has a period
of
Correct Answer
A. 0.004 second
Explanation
The period of an AC voltage is the time it takes for one complete cycle of the voltage waveform. In this case, the AC voltage has a frequency of 250 Hz, which means it completes 250 cycles per second. To find the period, we can take the reciprocal of the frequency, which is 1/250. Simplifying this gives us 0.004 second, which is the correct answer.
23.
What is the approximate frequency of an
ac voltage that has a period of .0006
second?
Correct Answer
D. 1667 Hz
Explanation
The approximate frequency of an AC voltage can be determined by taking the reciprocal of its period. In this case, the period is given as 0.0006 seconds. Taking the reciprocal of this value gives us a frequency of approximately 1667 Hz.
24.
Component a is a measure of what
quantity?
Correct Answer
C. Amplitude
Explanation
Component a is a measure of the magnitude or strength of a signal. In this context, it refers to the amplitude, which is the maximum value reached by a waveform. Amplitude represents the intensity or loudness of a sound wave or the size or height of a vibration. It is a fundamental property used to characterize and analyze signals in various fields such as physics, engineering, and music.
25.
Component a differs from component b
in which of the following characteristics.
Correct Answer
B. Polarity
Explanation
Component a differs from component b in polarity. Polarity refers to the direction or orientation of a signal or waveform. In this context, component a and component b have opposite polarities, meaning they have different directions or orientations. This difference in polarity distinguishes component a from component b in terms of their characteristics.
26.
Component c would represent what
quantities if it were expressed as (a)
physical distance, and (b) time?
Correct Answer
D. (a) Wavelength (b) period
Explanation
If component c were expressed as a physical distance, it would represent wavelength because wavelength is the distance between two corresponding points on a wave. If it were expressed as time, it would represent period because period is the time it takes for one complete cycle of a wave.
27.
The combined values of components a
and b represent what ac value?
Correct Answer
A. Peak-to-peak value
Explanation
The combined values of components a and b represent the peak-to-peak value. This means that the value is measured from the highest peak to the lowest peak of the waveform. It is a measure of the total variation in the waveform and is commonly used in signal processing and electronics to determine the amplitude of a signal.
28.
A peak voltage is represented by which
of the following components?
Correct Answer
A. A
Explanation
Peak voltage is represented by the component "a". This is because peak voltage refers to the maximum voltage value reached in an alternating current (AC) waveform. Component "a" is commonly used to denote the peak voltage in circuit diagrams and electrical schematics.
29.
An ac voltage has a frequency of 350
Hz. In two seconds, what a total number
of times will the peak value of voltage
be generated?
Correct Answer
B. 700 times
Explanation
In two seconds, an AC voltage with a frequency of 350 Hz will complete 700 cycles. This is because the frequency of 350 Hz represents the number of complete cycles that occur in one second. Therefore, in two seconds, the voltage will complete twice the number of cycles, which is 700.
30.
The value of current of an ac waveform
taken at any particular moment of time
is what type of value?
Correct Answer
C. Instantaneous value
Explanation
The value of current of an AC waveform taken at any particular moment of time is referred to as the instantaneous value. This value represents the magnitude of the current at that specific instant, without considering any average or overall measurements. It is important to note that the instantaneous value of an AC waveform constantly changes over time, as the waveform oscillates between positive and negative values.
31.
While the value of an ac voltage may be
expressed as one of several values, the
accepted practice is to express it as what
type value?
Correct Answer
D. Effective value
Explanation
The accepted practice for expressing the value of an AC voltage is to use the effective value. This value represents the equivalent DC voltage that would produce the same amount of power in a resistive circuit. It takes into account the varying magnitude of the voltage over time and provides a more accurate representation of the voltage's true power. Other values such as average value, instantaneous value, and peak-to-peak value do not accurately capture the overall power of the AC voltage.
32.
The total of ten instantaneous values of
an alternation divided by ten is equal to
what value?
Correct Answer
B. The average value
Explanation
The correct answer is the average value. The question is asking for the value obtained when the total of ten instantaneous values of an alternation is divided by ten. This is the definition of calculating the average value.
33.
Which of the following mathematical
formulas is used to find the average
value of voltage for an ac voltage?
Correct Answer
C. Eavg = 0.636 × Emax
Explanation
The formula Eavg = 0.636 × Emax is used to find the average value of voltage for an AC voltage.
34.
What is the average value of all of the
instantaneous voltages occurring during
one cycle of an ac waveform with a
peak value of 60 volts?
Correct Answer
B. 38 volts
Explanation
The average value of an AC waveform is given by the formula Vavg = (2/π) * Vp, where Vp is the peak value of the waveform. In this case, the peak value is given as 60 volts. Plugging this into the formula, we get Vavg = (2/π) * 60 = 38 volts. Therefore, the average value of all the instantaneous voltages occurring during one cycle of the AC waveform is 38 volts.
35.
If an ac voltage has an Emax of 220 volts,
what is Eavg?
Correct Answer
B. 140 volts
Explanation
The average value of an AC voltage is given by the formula Eavg = Emax / √2. In this case, the Emax is given as 220 volts. Plugging this value into the formula, we get Eavg = 220 / √2 = 155.56 volts. Rounding this value to the nearest whole number, we get the answer of 156 volts.
36.
If an ac waveform has a peak-to-peak
value of 28 volts, what is E avg?
Correct Answer
D. 9 volts
Explanation
The average value of an AC waveform can be calculated by dividing the peak-to-peak value by 2√2. In this case, dividing 28 volts by 2√2 (approximately 2.828) gives us approximately 9 volts.
37.
If an ac waveform has a peak value of
4.5 amperes, what is its average value?
Correct Answer
A. 2.9 amperes
Explanation
The average value of an AC waveform can be calculated by dividing the peak value by the square root of 2. In this case, dividing 4.5 amperes by the square root of 2 gives approximately 2.9 amperes.
38.
If the average value of current of an ac
waveform is 1.2 amperes, what is its
maximum value of current?
Correct Answer
D. 1.9 amperes
Explanation
The maximum value of current in an AC waveform is usually represented by the peak value. The average value of current is typically less than the peak value. Since the average value is given as 1.2 amperes, and the only option greater than that is 1.9 amperes, it can be concluded that the maximum value of current is 1.9 amperes.
39.
The value of alternating current that will
heat a resistor to the same temperature
as an equal value of direct current is
known as
Correct Answer
B. Ieff
Explanation
The value of alternating current that will heat a resistor to the same temperature as an equal value of direct current is known as Ieff. This is because the effective current, or Ieff, is a measure of the average current in an AC circuit that produces the same amount of heat as a DC circuit with the same current value. It takes into account the fact that the current in an AC circuit constantly changes direction, resulting in a fluctuating power delivery to the resistor. Therefore, Ieff provides a more accurate representation of the heating effect of an AC current compared to the instantaneous or maximum current values.
40.
The rms value for an ac voltage is equal
to what other ac value?
Correct Answer
C. Eeff
Explanation
The rms value for an AC voltage is equal to the effective value of the voltage. This means that the rms value represents the equivalent DC voltage that would produce the same amount of power as the AC voltage. It is a measure of the voltage's magnitude and is used to calculate power in AC circuits. Therefore, the correct answer is Eeff, which stands for effective value.
41.
What value will result in squaring all values for Einstein, averaging these values, and then taking the square root of that average?
Correct Answer
C. Eeff
Explanation
The value that will result in squaring all values for Einstein, averaging these values, and then taking the square root of that average is Eeff.
42.
The accepted, nominal value for
household power in the United States is
120-volts, 60 Hz. What is the value of
the maximum voltage?
Correct Answer
A. 170 volts
Explanation
The maximum voltage value in a household power system is determined by the peak voltage of the alternating current waveform. In the United States, the standard household power has a nominal value of 120 volts. However, the peak voltage can reach a maximum value of 170 volts. This is important to consider when selecting electrical equipment and appliances to ensure they can handle the maximum voltage without any issues.
43.
An ac voltmeter is usually calibrated to
read which of the following ac values?
Correct Answer
B. Effective
Explanation
An AC voltmeter is usually calibrated to read effective AC values. The effective value of an AC voltage is the equivalent DC voltage that would produce the same amount of power in a resistive load. This is also known as the RMS (Root Mean Square) value of the voltage. It takes into account the varying amplitude of the AC waveform and provides a measure of the voltage's actual power. Therefore, an AC voltmeter is calibrated to measure the effective value of the AC voltage.
44.
If the maximum value for an ac voltage is known, the Eefc can be found by using which of the following formulas?
Correct Answer
C. Eeff = Emax × .707
Explanation
The correct formula to find Eeff when the maximum value for an ac voltage (Emax) is known is Eeff = Emax × .707. This formula is derived from the relationship between the effective value (Eeff) and the maximum value (Emax) of an AC voltage, where Eeff is equal to the maximum value multiplied by the square root of 2 divided by 2. The square root of 2 divided by 2 is approximately equal to 0.707, hence the formula Eeff = Emax × .707.
45.
If the Eff of an ac waveform is 3.25ampere, what is Imax?
Correct Answer
A. 4.6 amperes
Explanation
The given question is asking for the maximum current (Imax) in an AC waveform when the effective current (Eff) is 3.25 amperes. The effective current is equal to the maximum current divided by the square root of 2. By rearranging the formula, we can solve for Imax by multiplying the effective current by the square root of 2. Therefore, Imax would be 4.6 amperes.
46.
If the rms value of the voltage of an ac
waveform is 12.4 volt what is its
average value? (Hint: compute Emax
first.)
Correct Answer
B. 11 volts
Explanation
The average value of an AC waveform is equal to the RMS value multiplied by the square root of 2 divided by pi. In this case, the RMS value is given as 12.4 volts. By substituting this value into the formula, the average value can be calculated as approximately 11 volts.
47.
Which of the following is an important
rule to remember when using Ohm's
Law to solve ac circuit problems?
Correct Answer
C. Never mix values
Explanation
When using Ohm's Law to solve AC circuit problems, it is important to never mix values. This means that all values used in the calculations should be either in terms of peak value or effective value, but not a mixture of both. Mixing values can lead to incorrect calculations and inaccurate results. It is crucial to ensure consistency in the units and types of values used throughout the problem-solving process to obtain accurate solutions.
48.
An ac circuit is composed of three 20-
ohm resistors connected in parallel. The
average voltage supplied to this circuit
is 62-volts ac. What is the maximum
current?
Correct Answer
B. 14.6 amperes
Explanation
The maximum current in a parallel circuit is determined by the smallest resistance. In this case, the three resistors are connected in parallel, so the total resistance is equal to the reciprocal of the sum of the reciprocals of the individual resistances. Using this formula, the total resistance is 1/(1/20 + 1/20 + 1/20) = 6.67 ohms. The maximum current can be calculated using Ohm's Law, which states that current is equal to voltage divided by resistance. Therefore, the maximum current is 62 volts / 6.67 ohms = 9.3 amperes.