FE Electrical Exam
(ANSWER AND EXPLANATION)
Carbon monoxide and oxygen react at 4000 K and 1 atm pressure in a closed, flexible container to produce carbon
dioxide. The standard enthalpy of formation for this reaction is -283kj/mol CO2. At equilibrium, the mole fractions are
0.03 oxygen, 0.89 carbon dioxide, respectfully. After equilibrium has been attained, the temperature of the system
suddenly decreases from 4000 K to 1000 K. Which of the following statements is correct?
A)The equilibrium constant will increase
B) The concentration of carbon monoxide will increase
C) The mole fraction of carbon dioxide will decrease
D) The reaction will stop
According to Le Chatelier's principle, when a stress is applied to a system in equilibrium shifts in such a way as to
relieve the stress. In this case, the stress is a decrease in temperature. When the temperature is decreased, the
system will respond by increasing the rate at which CO2 is produced since this is an exothermic reaction ( as
evidenced by the negative enthalpy of formation). The concentration of carbon dioxide and the equilibrium constant
will increase as a result. The answer is A
Kirchhoff's laws state which of the following?
A) voltages across the parallel branches are equal, and current through series branches are equal.
B) a voltage source in series with a resistor may be replaced by a current source in parallel with a resistor and vice
versa
C) The sum of the currents in branches compromising any closed loop in a circuit is zero, and the sum of all voltages
in branches connected to a common node is zero.
D) The sum of the currents flowing into a node is zero, and the sum of the voltages in the branches of any closed
loop of a circuit is zero.
Kirchhoff's current law states that as much current flows out of a node as flows into it. Kirchhoff's voltage law states
that the sum of the voltage drop around any closed loop is equal to the sum of the applied voltages. The answer is D
What is a passive element?
A)an element with reactance but no resistance
B) an element that plays no role in a circuit
C) an element whose characteristics are controlled by the characteristics of another element
D) an element that only stores, releases, or dissipates power.
Passive elements absorb and/or release energy. The answer is D
Which of the following is a correct definition for power factor in an alternating current circuit?
A)the ratio of apparent power to actual power
B) the ratio of resistance to impedance
C) the sine of the phase angle between voltage and current of the load
D) the ratio of impedance to resistance
Impedance is the complex sum of resistance and reactance. Considering the impedance triangle, the impedance can
be written as: Z=R/cos(theta)
The quantity cos(theta) is called the power factor. Theta is the impedance angle- the angle between voltage and
current.
Cos(theta)= R/Z
Therefore the answer is B
Which of the following is the best definition of enthalpy?
,A) the ratio of heat added to temperature change induced in a substance
B) the total amount of useful energy in a system
C) the heat required to cause a complete conversion between two phases at a constant temperature
D) the amount of energy in a system that is no longer available to do useful work
Enthalpy represents the total change in useful energy of a system. The answer is B
What does the triple point on a pressure-temperature diagram indicate?
A)the point at which a solid can be converted to a vapor without passing through the liquid phase
B) the point at which three phases can coexist
C) the point above which different phases are indistinguishable
D) the point at which a liquid is vaporized by the addition of heat
The triple point of a substance is a unique state at which solid, liquid, and gaseous phases can coexist. The answer is
B
A reduction in the relative humidity in a test chamber will result from which of the following?
A)an increase in the air temperature
B) a drop in the air temperature
C) a decrease in the partial pressure of water vapor
D) a reduction in the water vapor pressure in relation to the chamber temperatures
Relative humidity= (partial pressures of water vapor/ saturation pressure)
A decrease in the partial pressure of water vapor would reduce humidity. The answer is C.
Which of the following expressions correctly relates the power factor (pf) to real power (P), reactive power (Q), and
complex power (S)?
A) pf=P/Q
B) pf= Q/P
C) pf=P/S
D) pf= Q/S
The answer is C
If the magnitude of the potential difference is generated by a single conductor passing through a magnetic field, which
of the following statements is false?
A)The potential difference depends on the speed with which the conductor cuts the magnetic field
B) The potential difference depends on the length of the conductor that cuts the magnetic field
C) The potential difference depends on the magnetic field density that is present
D) The potential difference depends on the diameter of the conductor that cuts the magnetic field
The potential difference is the induced voltage described by Faraday's Law:
E= -Nd(theta)/(dt)
The change in the magnetic flux d(theta)/(dt), will be influenced by the length of the conductor but not the cross-
sectional area or diameter of the conductor. For a single conductor N=1. The answer is D
Which of the following statements is true for steady-state conditions in a circuit powered by a dry cell?
A) Voltage is dependent upon time
B) Inductors behave as short circuits
C) Capacitors behave as short circuits
D) Resistors behave as open circuits
Inductors have no resistance in a DC circuit; therefore, they will act as a short circuit. Capacitors have infinite
resistance; thus they act as an open circuit. Capacitors placed across the dry cell will accumulate charge. The answer
is B.
,Which of the following statements is true?
A) An ideal current source cannot be in parallel with a short circuit
B) An ideal voltage source can be in parallel with an open circuit
C) An ideal current source can be in series with an open circuit
D) An ideal voltage source cannot be in series with a with an ideal current source
If there is a complete circuit, ideal voltage and current sources deliver voltages and current at their rated values
regardless of the circuit parameters. This eliminates the "cannot be in" alternatives. No current will flow in an open
circuit, no matter how ideal the source is. This eliminates choice C. An ideal voltage source will still develop its full
voltage potential even without a full circuit. The answer is B
What measurements are required to determine the phase angle of a single-phase circuit?
A) the power is watts consumed by the circuit
B) the frequency, capacitance, and inductance
C) the power in watts, voltage, and current
D) the resistance, current, and voltage
The equation for power is
P= ½VmaxImaxcos(theta)=VrmsIrms*cos(theta)
Therefore, to find the phase angle, theta, the power, voltage, and current must be shown. The answer is C
An AC circuit consisting of a capacitor, an inductor, and a resistor in series is resonant when the
A)in-phase current equals the out-of-phase current
B) maximum current passes through the circuit
C) power dissipation is minimum
D) power factor is zero
In a resonant series-RLC circuit, impedance is a minimum and current is a maximum. The magnitude of the current is
the magnitude of the voltage divided by the magnitude of the impedance. The magnitude of the impedance is a
minimum when the imaginary part cancels (resonance). The answer is B
The polarity of the voltage to a DC motor is reversed. Which statement is true?
A) The rotor will not turn, because the commutator rectifies
B) The rotor will reverse direction
C) The rotor will rotate in the same direction
D) the motor will burn up.
The current through the armature windings will be reversed when the voltage polarity is reversed. The direction of the
magnetic flux is reversed, and the torque of the motor will be reversed. Therefore, the direction of the motor will be
reversed. The answer is B
The mechanical load to a DC motor is increased in a brief time from 100% to 102% of rated capacity. When the motor
is at 102% of rated capacity it will
A )stall
B) be destroyed
C) operate at rated torque
D) operate at a higher torque than rated torque
The rated value for mechanical load can be exceeded by a small percentage for a brief time without stalling or
damage to the motor. The rated value is established to keep the operation of the motor linear and to avoid excessive
, heating. During the time the motor is loaded to 102% of the rated capacity, it will produce approximately 102% of the
rated torque. The answer is D
Which of the following could serve as a polyphase inductor?
A) an induction motor
B) heating coils
C) a synchronous capacitor
D) a plating tank
Heating coils are essentially purely resistive and do not have a large inductive effect. A synchronous capacitor is a
synchronous motor that runs unloaded and draws a leading current, often used for power factor correction. A plating
tank is not an inductive load. The stator of a three-phase induction motor consists of three primary windings
connected in either a wye or delta configuration. The induction motor is essentially a three-phase inductor. The
answer is A
Depreciation allowance is best defined as
A) the value that a buyer will give a machine's owner at the end of the machine's useful life.
B) the amount awarded to industries involved in removing natural limited resources from the earth.
C) the amount used to recover the cost of an asset so that a replacement can be purchased
D) a factor whose use is regulated by federal law
Depression rates are closely regulated by federal law. Although depreciation does in fact result in a reduction in
income taxes, it never is able to fully recover the original cost of the asset. The answer is D
Which of the following five situations are examples of making manually exclusive decisions?
I. The maintenance department has requested a new air compressor and either a large paint booth or an additional
air compressor
II. The machine shop needs new inspection and locating equipment
III. The steno pool needs either a new, faster word processor or an additional office assistant
IV. The budget committee must decide among building employees" convenience store, an on-site cafeteria, an
enclosed pool, or an inhouse exercise room
V. The newly elected union representative must resign due to a conflict of interest
A) I,II, and IV
B) I, II, and V
C) I, III, and IV
D) II, III and V
Alternatives are mutually exclusive when selecting one precludes the others. Situations I, III, and IV require a
decision that will eliminate one part or another of the alternative. There is no alternative from which to choose in
situation II and IV. The answer is C
A cylinder with a frictionless piston contains an ideal gas at temperature T and pressure p. The gas expands
isothermally and reversibly until the pressure is p/3. Which statement is true regarding the work done by the gas
during expansion?
A) it is equal to the change in enthalpy of the gas
B) it is equal to the change in internal energy of the gas
C) it is equal to the heat absorbed by the gas
D) it is greater than the heat absorbed by the gas
Use the first law of thermodynamics
Q=deltaU + W
Since the internal energy remains constant during an isothermal process deltaU=0
Therefore Q=W
(ANSWER AND EXPLANATION)
Carbon monoxide and oxygen react at 4000 K and 1 atm pressure in a closed, flexible container to produce carbon
dioxide. The standard enthalpy of formation for this reaction is -283kj/mol CO2. At equilibrium, the mole fractions are
0.03 oxygen, 0.89 carbon dioxide, respectfully. After equilibrium has been attained, the temperature of the system
suddenly decreases from 4000 K to 1000 K. Which of the following statements is correct?
A)The equilibrium constant will increase
B) The concentration of carbon monoxide will increase
C) The mole fraction of carbon dioxide will decrease
D) The reaction will stop
According to Le Chatelier's principle, when a stress is applied to a system in equilibrium shifts in such a way as to
relieve the stress. In this case, the stress is a decrease in temperature. When the temperature is decreased, the
system will respond by increasing the rate at which CO2 is produced since this is an exothermic reaction ( as
evidenced by the negative enthalpy of formation). The concentration of carbon dioxide and the equilibrium constant
will increase as a result. The answer is A
Kirchhoff's laws state which of the following?
A) voltages across the parallel branches are equal, and current through series branches are equal.
B) a voltage source in series with a resistor may be replaced by a current source in parallel with a resistor and vice
versa
C) The sum of the currents in branches compromising any closed loop in a circuit is zero, and the sum of all voltages
in branches connected to a common node is zero.
D) The sum of the currents flowing into a node is zero, and the sum of the voltages in the branches of any closed
loop of a circuit is zero.
Kirchhoff's current law states that as much current flows out of a node as flows into it. Kirchhoff's voltage law states
that the sum of the voltage drop around any closed loop is equal to the sum of the applied voltages. The answer is D
What is a passive element?
A)an element with reactance but no resistance
B) an element that plays no role in a circuit
C) an element whose characteristics are controlled by the characteristics of another element
D) an element that only stores, releases, or dissipates power.
Passive elements absorb and/or release energy. The answer is D
Which of the following is a correct definition for power factor in an alternating current circuit?
A)the ratio of apparent power to actual power
B) the ratio of resistance to impedance
C) the sine of the phase angle between voltage and current of the load
D) the ratio of impedance to resistance
Impedance is the complex sum of resistance and reactance. Considering the impedance triangle, the impedance can
be written as: Z=R/cos(theta)
The quantity cos(theta) is called the power factor. Theta is the impedance angle- the angle between voltage and
current.
Cos(theta)= R/Z
Therefore the answer is B
Which of the following is the best definition of enthalpy?
,A) the ratio of heat added to temperature change induced in a substance
B) the total amount of useful energy in a system
C) the heat required to cause a complete conversion between two phases at a constant temperature
D) the amount of energy in a system that is no longer available to do useful work
Enthalpy represents the total change in useful energy of a system. The answer is B
What does the triple point on a pressure-temperature diagram indicate?
A)the point at which a solid can be converted to a vapor without passing through the liquid phase
B) the point at which three phases can coexist
C) the point above which different phases are indistinguishable
D) the point at which a liquid is vaporized by the addition of heat
The triple point of a substance is a unique state at which solid, liquid, and gaseous phases can coexist. The answer is
B
A reduction in the relative humidity in a test chamber will result from which of the following?
A)an increase in the air temperature
B) a drop in the air temperature
C) a decrease in the partial pressure of water vapor
D) a reduction in the water vapor pressure in relation to the chamber temperatures
Relative humidity= (partial pressures of water vapor/ saturation pressure)
A decrease in the partial pressure of water vapor would reduce humidity. The answer is C.
Which of the following expressions correctly relates the power factor (pf) to real power (P), reactive power (Q), and
complex power (S)?
A) pf=P/Q
B) pf= Q/P
C) pf=P/S
D) pf= Q/S
The answer is C
If the magnitude of the potential difference is generated by a single conductor passing through a magnetic field, which
of the following statements is false?
A)The potential difference depends on the speed with which the conductor cuts the magnetic field
B) The potential difference depends on the length of the conductor that cuts the magnetic field
C) The potential difference depends on the magnetic field density that is present
D) The potential difference depends on the diameter of the conductor that cuts the magnetic field
The potential difference is the induced voltage described by Faraday's Law:
E= -Nd(theta)/(dt)
The change in the magnetic flux d(theta)/(dt), will be influenced by the length of the conductor but not the cross-
sectional area or diameter of the conductor. For a single conductor N=1. The answer is D
Which of the following statements is true for steady-state conditions in a circuit powered by a dry cell?
A) Voltage is dependent upon time
B) Inductors behave as short circuits
C) Capacitors behave as short circuits
D) Resistors behave as open circuits
Inductors have no resistance in a DC circuit; therefore, they will act as a short circuit. Capacitors have infinite
resistance; thus they act as an open circuit. Capacitors placed across the dry cell will accumulate charge. The answer
is B.
,Which of the following statements is true?
A) An ideal current source cannot be in parallel with a short circuit
B) An ideal voltage source can be in parallel with an open circuit
C) An ideal current source can be in series with an open circuit
D) An ideal voltage source cannot be in series with a with an ideal current source
If there is a complete circuit, ideal voltage and current sources deliver voltages and current at their rated values
regardless of the circuit parameters. This eliminates the "cannot be in" alternatives. No current will flow in an open
circuit, no matter how ideal the source is. This eliminates choice C. An ideal voltage source will still develop its full
voltage potential even without a full circuit. The answer is B
What measurements are required to determine the phase angle of a single-phase circuit?
A) the power is watts consumed by the circuit
B) the frequency, capacitance, and inductance
C) the power in watts, voltage, and current
D) the resistance, current, and voltage
The equation for power is
P= ½VmaxImaxcos(theta)=VrmsIrms*cos(theta)
Therefore, to find the phase angle, theta, the power, voltage, and current must be shown. The answer is C
An AC circuit consisting of a capacitor, an inductor, and a resistor in series is resonant when the
A)in-phase current equals the out-of-phase current
B) maximum current passes through the circuit
C) power dissipation is minimum
D) power factor is zero
In a resonant series-RLC circuit, impedance is a minimum and current is a maximum. The magnitude of the current is
the magnitude of the voltage divided by the magnitude of the impedance. The magnitude of the impedance is a
minimum when the imaginary part cancels (resonance). The answer is B
The polarity of the voltage to a DC motor is reversed. Which statement is true?
A) The rotor will not turn, because the commutator rectifies
B) The rotor will reverse direction
C) The rotor will rotate in the same direction
D) the motor will burn up.
The current through the armature windings will be reversed when the voltage polarity is reversed. The direction of the
magnetic flux is reversed, and the torque of the motor will be reversed. Therefore, the direction of the motor will be
reversed. The answer is B
The mechanical load to a DC motor is increased in a brief time from 100% to 102% of rated capacity. When the motor
is at 102% of rated capacity it will
A )stall
B) be destroyed
C) operate at rated torque
D) operate at a higher torque than rated torque
The rated value for mechanical load can be exceeded by a small percentage for a brief time without stalling or
damage to the motor. The rated value is established to keep the operation of the motor linear and to avoid excessive
, heating. During the time the motor is loaded to 102% of the rated capacity, it will produce approximately 102% of the
rated torque. The answer is D
Which of the following could serve as a polyphase inductor?
A) an induction motor
B) heating coils
C) a synchronous capacitor
D) a plating tank
Heating coils are essentially purely resistive and do not have a large inductive effect. A synchronous capacitor is a
synchronous motor that runs unloaded and draws a leading current, often used for power factor correction. A plating
tank is not an inductive load. The stator of a three-phase induction motor consists of three primary windings
connected in either a wye or delta configuration. The induction motor is essentially a three-phase inductor. The
answer is A
Depreciation allowance is best defined as
A) the value that a buyer will give a machine's owner at the end of the machine's useful life.
B) the amount awarded to industries involved in removing natural limited resources from the earth.
C) the amount used to recover the cost of an asset so that a replacement can be purchased
D) a factor whose use is regulated by federal law
Depression rates are closely regulated by federal law. Although depreciation does in fact result in a reduction in
income taxes, it never is able to fully recover the original cost of the asset. The answer is D
Which of the following five situations are examples of making manually exclusive decisions?
I. The maintenance department has requested a new air compressor and either a large paint booth or an additional
air compressor
II. The machine shop needs new inspection and locating equipment
III. The steno pool needs either a new, faster word processor or an additional office assistant
IV. The budget committee must decide among building employees" convenience store, an on-site cafeteria, an
enclosed pool, or an inhouse exercise room
V. The newly elected union representative must resign due to a conflict of interest
A) I,II, and IV
B) I, II, and V
C) I, III, and IV
D) II, III and V
Alternatives are mutually exclusive when selecting one precludes the others. Situations I, III, and IV require a
decision that will eliminate one part or another of the alternative. There is no alternative from which to choose in
situation II and IV. The answer is C
A cylinder with a frictionless piston contains an ideal gas at temperature T and pressure p. The gas expands
isothermally and reversibly until the pressure is p/3. Which statement is true regarding the work done by the gas
during expansion?
A) it is equal to the change in enthalpy of the gas
B) it is equal to the change in internal energy of the gas
C) it is equal to the heat absorbed by the gas
D) it is greater than the heat absorbed by the gas
Use the first law of thermodynamics
Q=deltaU + W
Since the internal energy remains constant during an isothermal process deltaU=0
Therefore Q=W
