NEET Online Exam: Physics Quiz!

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NEET Online Exam: Physics Quiz! - Quiz

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Questions and Answers
  • 1. 

    Alternating current can be defined as current that varies in

    • A.

      Amplitude and direction

    • B.

      Magnitude and phase

    • C.

      Amplitude and time

    • D.

      time and phase

    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."

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  • 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?

    • A.

      A resistor placed in parallel with the load

    • B.

      A resistor placed in series with the load

    • C.

      A step-down transformer placed in series with load

    • D.

      A step-down transformer placed in parallel-with the load

    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.

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  • 3. 

    Alternating current has replaced direct current in modern transmission systems because it has which of the following advantages?

    • A.

      Ac can be transmitted with no line loss

    • B.

      Ac can be transmitted at higher current levels

    • C.

      Ac can be transmitted at lower voltage levels

    • D.

      Ac can be readily stepped up or down

    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.

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  • 4. 

    A waveform is a graphic plot of what quantities?

    • A.

      Current versus time

    • B.

      Amplitude versus time

    • C.

      Voltage versus amplitude

    • D.

      Magnitude versus amplitude

    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.

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  • 5. 

    Which of the following properties surrounds a current-carrying conductor?

    • A.

      A magnetic field

    • B.

      A repulsive force

    • C.

      An attractive force

    • D.

      An electrostatic field

    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.

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  • 6. 

    Which of the following statements accurately describes the magnetic field surrounding a current-carrying conductor?

    • A.

      It is parallel to and equal along all parts of the conductor

    • B.

      It is parallel to and maximum at the most negative part of the conductor

    • C.

      It is perpendicular to and equal along all parts of the conductor

    • D.

      It is perpendicular to the conductor and maximum at the most negative point of the 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.

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  • 7. 

    Which of the following factors determine(s) the intensity of a magnetic field surrounding a coil?

    • A.

      The amount of current flow through the coil

    • B.

      The type of core material

    • C.

      The number of turns in the conductor

    • D.

      All of the above

    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.

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  • 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

    • A.

      Voltage potential

    • B.

      Magnetic field

    • C.

      Current flow

    • D.

      South pole

    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.

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  • 9. 

    The power consumed in a conductor in realigning the atoms which set up the magnetic field is known as what type of loss?

    • A.

      Hysteresis loss

    • B.

      Magnetic loss

    • C.

      Field loss

    • D.

      Heat 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.

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  • 10. 

    The magnetic field surrounding a straight conductor is (a) what shape, and (b) is in what position relative to the conductor?

    • A.

      (a) Linked oblong (b) Parallel

    • B.

      (a) Concentric circles (b) Parallel

    • C.

      (a) Linked oblong (b) Perpendicular

    • D.

      (a) Concentric circles (b) Perpendicular

    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.

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  • 11. 

    Why is a two-pole magnetic field set up around a coil?

    • A.

      Because separate lines of magnetic force link and combine their effects

    • B.

      Because concentric lines of force cross at right angles and combine.

    • C.

      Because lines of force are separated and bent at the coil ends

    • D.

      Because separate lines of force are attracted to the two poles of the coi

    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.

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  • 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?

    • A.

      (a) Minimum, (b) maximum

    • B.

      (a) Minimum, (b) minimum

    • C.

      (a) Maximum, (b) maximum

    • D.

      (a) Maximum, (b) minimum

    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.

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  • 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?

    • A.

      A circle

    • B.

      A sine curve

    • C.

      A square wave

    • D.

      A straight line

    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.

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  • 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?

    • A.

      45º

    • B.

      90º

    • C.

      180º

    • D.

      270º

    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.

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  • 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?

    • A.

      (a) 0º , (b) 180º

    • B.

      (a) 0º , (b) 270º

    • C.

      (a) 90º , (b) 180º

    • D.

      (a) 90º , (b) 270º

    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.

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  • 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?

    • A.

      (a) 32, (b) 16

    • B.

      (a) 16, (b) 8

    • C.

      (a) 8, (b) 4

    • D.

      (a) 4, (b) 2

    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.

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  • 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?

    • A.

      (a) Current, (b) Magnetic flux, south to north

    • B.

      (a) Current, (b) Magnetic flux, north to south

    • C.

      (a) Magnetic flux, south to north, (b) Current

    • D.

      (a) Magnetic flux, north to south, (b) Current

    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.

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  • 18. 

    Continuous rotation of a conductor through magnetic lines of force will produce what type of (a) voltage and (b) waveform?

    • A.

      (a) Ac, (b) sine wave

    • B.

      (a) Dc, (b) continuous level

    • C.

      (a) Ac, (b) sawtooth

    • D.

      (a) Dc, (b) pulsating wave

    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.

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  • 19. 

    What is the term for the number of complete cycles of ac produced in one second?

    • A.

      Period

    • B.

      Waveform

    • C.

      Frequency

    • D.

      Wavelength

    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.

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  • 20. 

    What is the unit of measurement for frequency?

    • A.

      Cycle

    • B.

      Hertz

    • C.

      Period

    • D.

      Maxwell

    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.

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  • 21. 

    A loop of wire rotating at 60 rpm in a magnetic field will produce an ac voltage of what frequency?

    • A.

      1 Hz

    • B.

      60 Hz

    • C.

      120 Hz

    • D.

      360 Hz

    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.

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  • 22. 

    An ac voltage of 250 hertz has a period of

    • A.

      0.004 second

    • B.

      0.025 second

    • C.

      0.4 second

    • D.

      2.5 seconds

    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.

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  • 23. 

    What is the approximate frequency of an ac voltage that has a period of .0006 second?

    • A.

      6 Hz

    • B.

      16.67 Hz

    • C.

      600 Hz

    • D.

      1667 Hz

    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.

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  • 24. 

    Component a is a measure of what quantity?

    • A.

      Frequency

    • B.

      Polarity

    • C.

      Amplitude

    • D.

      Time

    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.

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  • 25. 

    Component a differs from component b in which of the following characteristics.

    • A.

      Frequency

    • B.

      Polarity

    • C.

      Amplitude

    • D.

      Period

    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.

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  • 26. 

    Component c would represent what quantities if it were expressed as (a) physical distance, and (b) time?

    • A.

      (a) Frequency (b) period

    • B.

      (a) Period (b) wavelength

    • C.

      (a) Frequency (b) wavelength

    • D.

      (a) Wavelength (b) period

    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.

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  • 27. 

    The combined values of components a and b represent what ac value?

    • A.

      Peak-to-peak value

    • B.

      Average value

    • C.

      Effective value

    • D.

      Instantaneous 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.

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  • 28. 

    A peak voltage is represented by which of the following components?

    • A.

      A

    • B.

      C

    • C.

      D

    • D.

      E

    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.

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  • 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?

    • A.

      350 times

    • B.

      700 times

    • C.

      1400 times

    • D.

      2800 times

    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.

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  • 30. 

    The value of current of an ac waveform taken at any particular moment of time is what type of value?

    • A.

      Average value

    • B.

      Effective value

    • C.

      Instantaneous value

    • D.

      Peak-to-peak 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.

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  • 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?

    • A.

      Average value

    • B.

      Instantaneous value

    • C.

      Peak-to-peak value

    • D.

      Effective 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.

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  • 32. 

    The total of ten instantaneous values of an alternation divided by ten is equal to what value?

    • A.

      The peak value

    • B.

      The average value

    • C.

      The instantaneous value

    • D.

      The effective 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.

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  • 33. 

    Which of the following mathematical formulas is used to find the average value of voltage for an ac voltage?

    • A.

      Eavg = 0.707 × Emax

    • B.

      Eavg = 1.414 × Eeff

    • C.

      Eavg = 0.636 × Emax

    • D.

      Eavg = 0.226 × Eeff

    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.

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  • 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?

    • A.

      0 volts

    • B.

      38 volts

    • C.

      76 volts

    • D.

      128 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.

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  • 35. 

    If an ac voltage has an Emax of 220 volts, what is Eavg?

    • A.

      50 volts

    • B.

      140 volts

    • C.

      156 volts

    • D.

      311 volts

    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.

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  • 36. 

    If an ac waveform has a peak-to-peak value of 28 volts, what is E avg?

    • A.

      40 volts

    • B.

      20 volts

    • C.

      18 volts

    • D.

      9 volts

    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.

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  • 37. 

    If an ac waveform has a peak value of 4.5 amperes, what is its average value?

    • A.

      2.9 amperes

    • B.

      3.2 amperes

    • C.

      5.7 amperes

    • D.

      6.4 amperes

    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.

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  • 38. 

    If the average value of current of an ac waveform is 1.2 amperes, what is its maximum value of current?

    • A.

      0.8 amperes

    • B.

      0.9 amperes

    • C.

      1.7 amperes

    • D.

      1.9 amperes

    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.

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  • 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

    • A.

      Iavg

    • B.

      Ieff

    • C.

      Iin

    • D.

      Imax

    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.

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  • 40. 

    The rms value for an ac voltage is equal to what other ac value?

    • A.

      Eavg

    • B.

      Emax

    • C.

      Eeff

    • D.

      Ein

    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.

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  • 41. 

    What value will result in squaring all values for Einstein, averaging these values, and then taking the square root of that average?

    • A.

      Eavg

    • B.

      Emax

    • C.

      Eeff

    • D.

      Ein

    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.

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  • 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?

    • A.

      170 volts

    • B.

      120 volts

    • C.

      85 volts

    • D.

      76 volts

    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.

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  • 43. 

    An ac voltmeter is usually calibrated to read which of the following ac values?

    • A.

      Average

    • B.

      Effective

    • C.

      Peak

    • D.

      Peak-to-peak

    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.

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  • 44. 

    If the maximum value for an ac voltage is known, the Eefc can be found by using which of the following formulas?

    • A.

      Eeff = Emax/.636

    • B.

      Eeff = Emax/.707

    • C.

      Eeff = Emax × .707

    • D.

      Eeff = Emax × 1.414

    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.

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  • 45. 

    If the Eff of an ac waveform is 3.25ampere, what is Imax?

    • A.

      4.6 amperes

    • B.

      2.3 amperes

    • C.

      2.1 amperes

    • D.

      1.6 amperes

    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.

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  • 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.)

    • A.

      8 volts

    • B.

      11 volts

    • C.

      15 volts

    • D.

      18 volts

    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.

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  • 47. 

    Which of the following is an important rule to remember when using Ohm's Law to solve ac circuit problems?

    • A.

      Always solve for resistance first

    • B.

      Give the answer as effective value

    • C.

      Never mix values

    • D.

      Convert all given values to effective before attempting to solve

    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.

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  • 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?

    • A.

      9.3 amperes

    • B.

      14.6 amperes

    • C.

      17.5 amperes

    • D.

      22.5 amperes

    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.

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