A.C. Circuits Final
A sine wave with a frequency of 12kHz is changing at a faster rate than a sine wave with a frequency of
20 kHz.
With 100V of primary voltage and a 1:3 turns ratio, the output voltage will be
300 v
Engineering notation
A system for representing any number as a one-, two-, or three-digit number times a power of ten with an exponent that is a multiple of 3
The unit of measurement for current is the
Ampere
To obtain the resistance in Ohms, you must express the value of I in __ and the value of V in __.
Amperes, Volts
Accuracy
An indication of the range of error in a measurement
Which of the following are common applications of electronics?
Computers, consumer products, automation, and communications systems.
Resistance limits the _____.
Current
A Wheatstone bridge is balanced when its output voltage is negative.
False
A capacitor stores voltage in its electromagnetic field
False
A high-pass filter acts as a lag circuit.
False
A maintenance issue with induction motors is brush replacement.
False
A power supply that has a negative output voltage absorbs power from the load.
False
A rheostat performs the same function as a potentiometer
False
A series circuit can have more than one path for current.
False
A series connection provides two or more paths for current to flow
False
A sine wave with a peak value of 10 V has the same heating effect as a 10 V dc source.
False
A solenoid is a form of electromagnetic switch that opens and closes mechanical contacts.
False
A transformer can be used to step-up (increase) Power
False
A transformer can pass a steady state DC from the primary to the secondary
False
An electronic device which stores an electric charge is known as an inductor
False
At the series resonant frequency, the RLC circuit is resistive and the current is minimum.
False
Attenuation is the ratio of input voltage to output voltage.
False
Below the parallel resonant frequency, the circuit is predominately capacitive.
False
Capacitive reactance is proportional to the applied frequency.
False
Current lags the voltage by 90 degrees in a capacitor
False
Energy is stored in a capacitor in a magnetic field, concentrated in the dielectric
False
Energy is stored in an inductor in its electrostatic filed
False
If one resistor is connected in series with a parallel combination, the series resistor will always have a larger voltage drop than the parallel resistors.
False
If the voltage across a resistor doubles, the power also doubles.
False
If there is direct current in the transformer primary, there will also be direct current in the secondary.
False
If two series resistors are different sizes, the larger resistor will have the larger current.
False
In a brushless motor, the magnetic field is supplied by permanent magnets.
False
In a five-brand precision resistor, the fourth band is the tolerance band
False
In a parallel circuit, the voltage is larger across a larger resistor and smaller across a smaller resistor.
False
In a series RC lag circuit, the output is taken across the resistor.
False
In a series-parallel combinational circuit, the same current will always be in parallel resistors.
False
In a three-phase electrical system, the phases are separated by 60°.
False
In an automotive alternator, the output current is taken from the rotor through slip rings.
False
Increasing voltage while maintaining the same resistance will cause current to decrease
False
Inductive reactance is inversely proportional to frequency.
False
Inductors have no resistance.
False
Inductors in parallel increase the total inductance in the circuit
False
Kirchhoff's voltage law is valid only if a loop contains a voltage source.
False
Ohm's law cannot be applied to reactive circuits.
False
Ohm's law for a magnetic circuit gives the relationship between flux density, magnetomotive force, and reluctance.
False
Phasors can be used to represent complex quantities.
False
Power factor is determined by the magnitudes of the voltage and current.
False
R + XL is a phasor sum.
False
The apparent power rating of a transformer is expressed in watts.
False
The decibel is a unit for expressing the ratio of one frequency to another.
False
The kilowatt-hour is a unit of power.
False
The number of neutrons in the nucleus is the atomic number of that elecment
False
The output of a band-stop filter is maximum at the resonant frequency.
False
The power rating of a resistor should always be less than the required power dissipation in the circuit.
False
The product-over-sum rule works for any number of parallel resistors.
False
The rms and average value of a sine wave are the same.
False
The speed of a generator can be controlled with a rheostat in the field windings.
False
The three basic measurements that can be done by a DMM are voltage, current, and power
False
The total impedance of a series RL circuit is the algebraic sum of the resistance and the inductive reactance.
False
The total impedance of a series RLC circuit is the algebraic sum of R, XC, and XL.
False
The total power dissipated by parallel resistors can be larger than the power supplied by the source.
False
The total reactance of series capacitors is the product-over-sum of the individual reactances.
False
The total resistance of a series circuit can be less than the largest resistor in that circuit.
False
The two windings in a basic transformer are called the primary and the tertiary.
False
The unit for measuring magnetomotive force (mmf) is the volt.
False
The unit of charge is the ampere
False
Two forms of complex numbers are rectangular and circular.
False
Voltage lags current in an inductor
False
Voltage leads current in a capacitor.
False
When a load resistor is connected across a voltage divider output, the output voltage increases
False
When a new path is added to a parallel circuit, the total resistance goes up.
False
When measuring dc voltage, the input resistance of an analog multimeter is the same no matter what scale it is used on.
False
When microamps and megohms are multiplied, the result is microvolts.
False
When two capacitors are in parallel with a voltage source, the smaller capacitor will have the larger voltage.
False
When two resistors are in parallel, the smaller resistor will have the smaller power dissipation.
False
A group of magnetic force lines going from the north pole of a magnet to the south pole is called
Magnetic Flux
The symbol for a resistor is
R
Two hundred joules of energy are consumed in 10 s.
The power is 20 W.
1. If a sine wave voltage is applied to a series RL circuit, the current is also a sine wave.
True
A Wheatstone bridge can be used to precisely measure resistance.
True
A capacitor appears as an open to a constant dc.
True
A charged capacitor could be considered a voltage source
True
A circular mil is a unit of area
True
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
True
A harmonic frequency is always an integral (odd or even) multiple of the fundamental frequency
True
A hysteresis curve is a plot of flux density (B) as a function of field intensity (H).
True
A larger-value load resistor has a smaller loading effect on a circuit.
True
A loaded voltage divider is a common application of a series-parallel circuit
True
A mathematical relationship between current, voltage, and resistance was determined by George Ohm
True
A parallel connection provides two or more paths for current to flow
True
A self-excited dc generator will normally have enough residual magnetism in the field magnets to start the generator producing voltage at the output when it is first turned on.
True
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
True
A strain gauge changes resistance in response to an applied force
True
A synchronous motor can be used when constant speed is required.
True
A transformer can be used to step-down (decrease) voltage
True
A transformer can be used to step-up (increase) voltage
True
A transformer can have more than two windings.
True
A transformer consists of two or more coils, sharing a common core, or placed close together, and are magnetically coupled
True
A transformer is based on the principle of mutual inductance.
True
A volt can be defined in terms of energy per charge
True
A voltage divider is a series arrangement of resistors
True
Admittance is the reciprocal of impedance.
True
All circuits must have a complete path for current
True
An R/2R ladder is used in analog-to-digital converters.
True
An inductor opposes any change in its current
True
At parallel resonance, the total impedance of an RLC circuit is maximum.
True
Below the resonant frequency, a series RLC circuit is predominately capacitive.
True
Capacitance is the measure of a capacitor's ability to store an electrical charge
True
Conductance is the reciprocal of resistance.
True
Energy in a battery is stored in the form of chemical energy
True
Exceeding the dielectric strength of a capacitor means you have applied too high a voltage, and probably destroyed the capacitor
True
Frequency is the reciprocal of the period
True
Ideally, an inductor appears as a short to dc.
True
If the current through a resistor doubles, the power increases by four.
True
If the output voltage of a band-pass filter is 1 V at the resonant frequency, it is 0.707 V at the critical frequencies.
True
If the total resistance of a circuit increases, current decreases.
True
If three equal resistors are used in a voltage divider, the voltage across each one will be one-third of the source voltage.
True
If two series resistors are different sizes, the larger resistor will have the larger voltage.
True
Impedance matching is based on the of reflected load.
True
In a series RL lag circuit, the output is taken across the resistor.
True
In a step-up transformer, the secondary has more turns of wire than does the primary
True
In an RC low-pass filter, the output is taken across the capacitor.
True
In an RL high-pass filter, the output is taken across the inductor.
True
In an ideal parallel RLC circuit, the total current is zero at resonance.
True
In the current-divider formula the quantity is a fraction that is never greater than 1.
True
Inductance is proportional to the square of the number of windings
True
Kilo equals 1,000 times the base unit
True
Magnetic fields can exert forces without objects physically touching
True
Mutual inductance is defined as the inductance between two coils that are coupled by a magnetic field
True
Normally, a DMM will have a small loading effect on a circuit.
True
One watt is equal to one joule per second.
True
Parallel resistors are always connected between the same pair of nodes.
True
Power factor is determined by the phase angle between voltage and current.
True
Roll-off is the rate at which the output of a low-pass filter decreases above the critical frequency.
True
Selectivity of a resonant circuit is better when the bandwidth is narrow.
True
Susceptance is the reciprocal of impedance.
True
The amount of heat that a resistor can dissipate is proportional to its surface area.
True
The amount of voltage induced in a coil is directly proportional to the rate of change of the magnetic field with respect to the coil.
True
The area of the plates of a capacitor is proportional to the capacitance.
True
The average value of a sine wave is zero
True
The bandwidth of a low-pass filter ideally extends from 0 Hz up to a specified critical frequency.
True
The bandwidth of a parallel resonant circuit is the difference between the upper and lower critical frequencies.
True
The current entering a point in a circuit is equal to the current leaving the point
True
The current through a capacitor is always maximum at the start of the first time constant
True
The frequency at which resonance occurs in a band-pass filter is sometimes called the center frequency.
True
The imaginary axis and real axis are parts of the complex plane.
True
The impedance in a reactive circuit is dependent on frequency.
True
The impedance in any RL circuit increases with frequency.
True
The impedance of a series RC circuit can be expressed as a complex quantity.
True
The impedance of an RL circuit can be expressed as a phasor quantity using complex numbers.
True
The inductor always opposes a change in current, even a transient DC current
True
The length of a phasor is called the magnitude
True
The material used in between the plates of a capacitor is called the dielectric
True
The peak value of a sine wave is the same as its amplitude.
True
The period of a 60 Hz sine wave is 16.7 ms.
True
The power developed by a motor is proportional to its torque.
True
The power dissipated by the resistors in a series circuit is the same as the power supplied by the source.
True
The purpose of an exciter is to supply dc rotor current to an alternator.
True
The relationship between voltage and current in a resistor is linear.
True
The tesla (T) and the gauss (G) are both units for magnetic flux density.
True
The total (equivalent) resistance in a parallel circuit is always less than the lowest value resistor in the circuit
True
The total current entering a node is always equal to the total current leaving the node.
True
The total reactance of a series RLC circuit is the difference between the capacitive reactance and the inductive reactance.
True
The total reactance of series inductors is the sum of the individual reactances.
True
The total resistance of parallel resistors is always smaller than the smallest resistor.
True
The turns ratio of a transformer determines the ratio of the output voltage to the input voltage.
True
The unit of inductive reactance is the ohm.
True
The unit of reactive power is the VAR.
True
The voltage across a resistor is directly proportional to the current through it.
True
There are 360 degrees in a complete cycle of a sine wave
True
There is no valid electrical reason for installing flashlight batteries so that they are not all in the same direction.
True
Three-phase transformers consist of delta and/or wye connections of the windings.
True
To find the total conductance of parallel resistors, you can add the conductance of each of the resistors.
True
To produce an induced voltage in a coil, the magnetic field surrounding it can be changed.
True
Transformers are used only for ac voltages.
True
Unlike magnetic poles attract each other, and like magnetic poles repel each other
True
Voltage leads the current in an indcuctor
True
Voltage leads the current in terms of phase in a series RC circuit.
True
Voltage leads the current in terms of phase in a series RL circuit.
True
Watt's law states that power equals voltage times current.
True
When a capacitor is charging or discharging between two levels, the charge on the capacitor changes by 63% of the difference in one time constant.
True
When a load is connected to a transformer, the power in the load is ideally equal to the power in the primary.
True
When a new path is added to a parallel circuit, the total current goes up.
True
When analyzing a circuit problem, you should consider the conditions under which it failed.
True
When measuring dc voltage, the input resistance of a DMM is the same no matter what scale it is used on.
True
When milliamps and kilohms are multiplied together, the result is volts.
True
When two capacitors are in series with a voltage source, the smaller capacitor will have the larger voltage.
True
When two or more components are connected across the same voltage source, they are in parallel
True
Within limits, a regulated power supply can automatically keep the output voltage constant even if the load changes.
True
You cannot multiply or divide complex numbers.
True
The unit of measurement for voltage is the
Volt
The symbol for power is
W
Power is measured in
Watts
The difference between alternating current (ac) and direct current (dc) is
ac changes direction and dc does not.
When current flow tries to decrease in an inductor, the magnetic field ________ and the voltage polarity across the inductor ________.
collapses, reverses
Free electrons make __ possible
current
Ohm's law states that voltage equals
current times resistance
Magnetomotive force is
directly proportional to the number of turns in the coil, and directly proportional to the current through the coil.
Power can be defined as the rate at which
energy is used
During each cycle, a sine wave reaches a peak value
four times.
To measure current with an ammeter, connect the ammeter
in the current path
In an inductive circuit, reactance will
increase with frequency increase
Opposition to current flow without the dissipation of energy in an inductor is called
inductive reactance
The materials with the fewest free electrons are classified as
insulators
One time constant can be solved by
multiplying capacitance by resistance
An atom is the smallest particle of an element that retains the characteristics
of that element
A phasor represents the
phase angle.
When analyzing a series-parallel circuit, the circuit should be
reduced down to one series circuit
The formula used to determine total inductance when inductors are connected in parallel is similar to
series capacitors
When the voltage across a resistor is doubled
the current will double
Error
the difference between the true of best-accepted value of some quality and the measure value
An example of an electromagnetic device that also uses a permanent magnet is
the loudspeaker
If it takes 300 ms to use 10,000 J of energy
the power is 33.3 kW
An example of an electromagnetic device is
the relay, a tape recording head, the solenoid, and the loudspeaker.
The total resistance of a series circuit is equal to
the sum of all the resistance values
In an inductor
the voltage leads the current by 90 degrees.
When finding the total resistance of a series-parallel combination, the most important step os
to define the series and parallel relationships
A potentiometer is a
voltage-control device, variable resistor, and 3-terminal device
An advantage of a three-phase induction motor is that it has a
wound rotor.