Motors And Transformers
This quiz is designed to evaluate one's knowledge of motors and transformers commonly used in industry. It is also designed to evaluate knowledge of basic AC and DC electrical fundamentals.
Questions and Answers
- 1.
The magnetically operated device that can change values of voltage, current, and impedance without changing the frequncy is the
- A.
Converter
- B.
Inverter
- C.
Transformer
- D.
Transistor
Correct Answer
C. TransformerExplanation
A transformer is a magnetically operated device that can change the values of voltage, current, and impedance without changing the frequency. It consists of two coils, known as the primary and secondary coils, which are wound around a common magnetic core. When an alternating current passes through the primary coil, it creates a changing magnetic field, which induces a voltage in the secondary coil. This allows for the transformation of electrical energy from one voltage level to another, without affecting the frequency of the current.Rate this question:
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- 2.
In a transformr, the turns of the primary wire compared to the turns of the secondary wire is called the ______ ratio.
- A.
Isolation
- B.
Step-up
- C.
Step-down
- D.
Turns
Correct Answer
D. TurnsExplanation
The turns ratio in a transformer refers to the ratio of the number of turns in the primary coil to the number of turns in the secondary coil. It is a crucial parameter that determines the voltage transformation capabilities of the transformer. By adjusting the turns ratio, transformers can step up or step down the input voltage to the desired level. Therefore, the correct answer is "turns."Rate this question:
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- 3.
In a transformer, even when no load is connected, there is a small current required to magnetize the core. It is called the ____ current.
- A.
Excitation
- B.
Primary
- C.
Secondary
- D.
Isolation
Correct Answer
A. ExcitationExplanation
In a transformer, even when no load is connected, there is a small current required to magnetize the core. This current is known as the excitation current. It is necessary to create a magnetic field in the core which allows for the transfer of energy between the primary and secondary coils of the transformer. The excitation current is essential for the proper functioning of the transformer and ensuring efficient power transfer.Rate this question:
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- 4.
A transformer in which the secondary voltage is less than the primary voltage is called a ____ transformer.
- A.
Step-up
- B.
Step-down
- C.
Isolation
- D.
Auto
Correct Answer
B. Step-downExplanation
A transformer in which the secondary voltage is less than the primary voltage is called a step-down transformer. This type of transformer is designed to lower the voltage level from the primary side to the secondary side. It is commonly used in power distribution systems to decrease high voltage levels to a safer and more usable voltage for residential and commercial applications.Rate this question:
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- 5.
The industrial use transformer that normally has 240v or 480v primary and a 120 v secondary is called a(n) ____ transformer.
- A.
Auto
- B.
Distribution
- C.
Isolation
- D.
Control
Correct Answer
D. ControlExplanation
The correct answer is "control" because a control transformer is typically used in industrial settings to provide power for control circuits. These transformers have a primary voltage of either 240v or 480v and a secondary voltage of 120v, which is suitable for powering control devices and equipment. They are designed to provide a stable and reliable power supply for control systems, ensuring proper functioning and operation.Rate this question:
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- 6.
A wye-delta transformer has its____ connected as a wye and its connected as a delta.
- A.
Secondary, primary
- B.
Primary, secondary
Correct Answer
B. Primary, secondaryExplanation
A wye-delta transformer has its primary connected as a wye and its secondary connected as a delta. This means that the primary winding of the transformer is connected in a wye configuration, where the three ends of the winding are connected to a common point, while the secondary winding is connected in a delta configuration, where the end of one winding is connected to the start of the next winding in a triangular loop. This configuration allows for the transformation of voltage and current between the primary and secondary sides of the transformer.Rate this question:
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- 7.
A delta-wye transformer has its____ connected as a delta and its connected as a wye.
- A.
Secondary, primary
- B.
Primary, secondary
Correct Answer
B. Primary, secondaryExplanation
A delta-wye transformer has its primary connected as a delta and its secondary connected as a wye. This means that the primary winding of the transformer is connected in a delta configuration, where the ends of each winding are connected to form a closed loop. On the other hand, the secondary winding is connected in a wye configuration, where one end of each winding is connected to a common neutral point, forming a star-like shape. This configuration allows for different voltage levels between the primary and secondary sides of the transformer.Rate this question:
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- 8.
An open delta connection is made using ____ single-phase transformers.
- A.
One
- B.
Two
- C.
Three
- D.
Four
Correct Answer
B. TwoExplanation
An open delta connection is made using two single-phase transformers. This type of connection is used when one transformer in a three-phase system fails, and it allows the system to continue operating with reduced capacity until the faulty transformer is repaired or replaced. The two remaining transformers are connected in a triangular arrangement, with one transformer serving as a common center point and the other two forming the open delta. This configuration allows for the generation of a three-phase supply, although at a reduced capacity compared to a fully operational three-phase system.Rate this question:
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- 9.
When connecting three transformers for three phase use with the delta secondary, a voltage test should be done before closing the secondary. The correct voltage reading is
- A.
The rated secondary voltage value
- B.
Twice the rated secondary voltage value
- C.
Zero volts
- D.
The sum of the the three transformer primaries
Correct Answer
C. Zero voltsExplanation
When connecting three transformers for three phase use with the delta secondary, a voltage test should be done before closing the secondary. The correct voltage reading is zero volts because in a delta connection, the secondary windings form a closed loop with no neutral connection. Therefore, there is no voltage present between any two points in the secondary winding, resulting in a reading of zero volts.Rate this question:
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- 10.
When using an open delta with a center tapped transformer, on wire is the "high leg." The high leg is the one that
- A.
Has the highest voltage measured to ground
- B.
Has the lowest voltage measured to ground
- C.
Has the most amperage
- D.
Is mounted highest on the panel
Correct Answer
A. Has the highest voltage measured to groundExplanation
In an open delta configuration with a center tapped transformer, one of the wires is designated as the "high leg." This high leg has the highest voltage measured to ground compared to the other wires. This is because the center tapped transformer allows for a higher voltage to be produced on this particular leg.Rate this question:
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- 11.
In an open delta with single phase loads, the high leg must be identified by
- A.
Using an orange wire
- B.
Tagging
- C.
Both a and b above
- D.
Either a or b above
Correct Answer
D. Either a or b aboveExplanation
In an open delta with single phase loads, the high leg can be identified either by using an orange wire or by tagging it. Both methods are acceptable for identifying the high leg in this scenario.Rate this question:
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- 12.
A transformer has a 240v primary and a 60v secondary. With a 5 ohm load connected, what is the primary volt amps?
- A.
12 amps
- B.
3 amps
- C.
0.75 amps
- D.
48 amps
Correct Answer
B. 3 ampsExplanation
The primary volt amps can be calculated using the formula Vp x Ip = Vs x Is, where Vp is the primary voltage, Ip is the primary current, Vs is the secondary voltage, and Is is the secondary current. In this case, Vp is 240V, Vs is 60V, and Is is 5 ohms. Rearranging the formula, we can solve for Ip: Ip = (Vs x Is) / Vp = (60V x 5A) / 240V = 300VA / 240V = 1.25A. Therefore, the primary volt amps is 3 amps.Rate this question:
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- 13.
A transformer has a 240v primary and a 120v secondary. With a 30 ohm load connected, what is the primary volt amps?
- A.
4
- B.
8
- C.
480
- D.
960
Correct Answer
C. 480Explanation
The primary volt amps can be calculated using the formula V x I, where V is the voltage and I is the current. In this case, the voltage is 240V and the current can be found using Ohm's law, which states that V = I x R, where R is the resistance. Given that the load connected is 30 ohms, the current can be calculated as I = V/R = 240V/30 ohms = 8A. Therefore, the primary volt amps is 240V x 8A = 480.Rate this question:
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- 14.
A transformer supplying a house with 120 / 240 volts has a secondary whic is center tapped. The conductor connected to the center is called the ____ conductor.
- A.
Equipment ground
- B.
Hot
- C.
Neutral
- D.
Ungrounded
Correct Answer
C. NeutralExplanation
The conductor connected to the center of a center-tapped transformer's secondary is called the neutral conductor. This conductor carries the return current from the load back to the transformer, providing a reference point for the voltage in the circuit. It is typically connected to the ground at the main service panel to ensure proper grounding and safety.Rate this question:
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- 15.
In an isolation transformer, all windings will have the same number of volts per turn.
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
In an isolation transformer, all windings will have the same number of volts per turn. This is because an isolation transformer is designed to provide electrical isolation between the input and output circuits. To achieve this, the primary and secondary windings are wound on separate coils, ensuring that the voltage remains the same per turn on each winding. This helps to prevent any potential voltage imbalances or fluctuations between the input and output circuits, ensuring safety and protection for connected devices.Rate this question:
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- 16.
When single phase loads are tied to a three phase transformer, the phase currents of the transformer will be automatically balanced.
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
When single phase loads are tied to a three phase transformer, the phase currents of the transformer will not be automatically balanced. This is because single phase loads draw different amounts of current from each phase, resulting in an imbalance. To achieve balanced currents, additional measures such as using a phase converter or connecting the loads evenly across the three phases are required.Rate this question:
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- 17.
A transformer in which the primary and secondary are phsically separated and not connected by a conductor is called a(n) ____ transformer.
- A.
Isolation
- B.
Step up
- C.
Step down
- D.
Turns
Correct Answer
A. IsolationExplanation
An isolation transformer is a type of transformer where the primary and secondary windings are physically separated and not connected by a conductor. This design ensures that there is no direct electrical connection between the input and output, providing electrical isolation and protecting against electrical shock and interference. It is commonly used in medical equipment, audio systems, and sensitive electronic devices to provide a safe and isolated power supply.Rate this question:
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- 18.
A transformer tape wound core is assembled by
- A.
Stacking small indivisual sheets of metal
- B.
Winding a long continuous tape of metal into a spiral
- C.
Casting a solid core and wrapping it with tape
- D.
Bolting together two halves
Correct Answer
B. Winding a long continuous tape of metal into a spiralExplanation
The correct answer is winding a long continuous tape of metal into a spiral. This is the process of assembling a transformer tape wound core. Instead of using individual sheets of metal or casting a solid core, the core is made by continuously winding a long tape of metal into a spiral shape. This method allows for a more efficient and compact design, as the spiral shape maximizes the magnetic flux and reduces energy losses. Bolting together two halves is not the correct answer as it does not involve the winding of a continuous tape.Rate this question:
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- 19.
A transformer that does not isolate the output from the input is called a(n) ____ transformer.
- A.
Distribution
- B.
Step up
- C.
Auto
- D.
Control
Correct Answer
C. AutoExplanation
An auto transformer is a type of transformer that does not provide electrical isolation between the input and output. Instead, it uses a single winding with taps to provide different voltage levels. This design allows for more efficient power transfer but does not provide the same level of safety as an isolation transformer.Rate this question:
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- 20.
The transformer winding which is the output winding is called the
- A.
Primary
- B.
Secondary
- C.
Tertiary
- D.
Tapped
Correct Answer
B. SecondaryExplanation
The transformer winding which is the output winding is called the secondary. The secondary winding is responsible for transferring the electrical energy from the primary winding to the load. It typically has a different number of turns than the primary winding, which allows for the transformation of voltage and current levels. The secondary winding is connected to the load and provides the desired output voltage or current.Rate this question:
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- 21.
The basis for understanding magnetic principles is the ____ theory of magnetism.
Correct Answer
electronExplanation
The correct answer is "electron" because the electron theory of magnetism explains the fundamental principles of how magnets work. According to this theory, magnets are formed by the alignment of electrons in the atoms of certain materials, which creates a magnetic field. The movement of electrons within atoms and their spin contribute to the magnetic properties of materials. Understanding the behavior of electrons is essential in comprehending the principles of magnetism.Rate this question:
- 22.
Three naturally magnetic metals are ____, ____, and ____.
Correct Answer
iron, nickel, cobaltExplanation
Iron, nickel, and cobalt are considered naturally magnetic metals because they possess magnetic properties even in their pure form. These metals have unpaired electrons in their outermost energy level, which allows them to align their magnetic moments and create a magnetic field. This property makes them useful in various applications, such as in the production of magnets, electrical devices, and magnetic storage media.Rate this question:
- 23.
When atoms in magnetic materials become ions, magnetic regions called ____ ____ are produced
Correct Answer
magnetic domainsExplanation
When atoms in magnetic materials become ions, they lose or gain electrons, resulting in the creation of magnetic regions called magnetic domains. These domains consist of groups of atoms with aligned magnetic moments, which contribute to the overall magnetization of the material. The formation of magnetic domains is essential for the magnetic properties exhibited by magnetic materials, as it allows for the alignment of magnetic moments and the generation of a magnetic field.Rate this question:
- 24.
Four effects that can demagnetize a magnet are ____, ____, ____, and ____.
Correct Answer
vibrations, striking, heat, AC fieldExplanation
Vibrations, striking, heat, and AC field are four effects that can demagnetize a magnet. Vibrations can cause the magnetic domains within the magnet to become misaligned, resulting in a loss of magnetism. Striking the magnet can also disrupt the alignment of the domains, leading to demagnetization. Heat can cause the magnetic material to lose its magnetism by altering the alignment of the domains. Lastly, an alternating current (AC) field can induce eddy currents within the magnet, which can generate heat and cause demagnetization.Rate this question:
- 25.
Magnets are surrounded by fields that exit the ____ pole and enter the ____ pole.
Correct Answer
north, southExplanation
Magnets have a magnetic field that extends from the north pole to the south pole. This means that the field lines exit the magnet at the north pole and enter the magnet at the south pole. This is a fundamental property of magnets, where the north and south poles attract each other due to the flow of magnetic field lines.Rate this question:
- 26.
When a current passes through a conductor, a _____ field is produced that is proportional to the ____.
Correct Answer
magnetic, currentExplanation
When a current passes through a conductor, it creates a magnetic field around the conductor. The strength of this magnetic field is directly proportional to the amount of current flowing through the conductor. Therefore, the correct answer is that a magnetic field is produced that is proportional to the current.Rate this question:
- 27.
Direct current flowing through a coil will produce a magnetic field that is ____, while alternating current will produce a field that is ____.
Correct Answer
constant, changingExplanation
Direct current flowing through a coil will produce a magnetic field that remains constant in strength and direction. This is because the flow of electrons in a direct current is unidirectional, causing a consistent magnetic field to be generated around the coil. On the other hand, alternating current constantly changes direction, causing the flow of electrons to reverse periodically. This results in a magnetic field that alternates in strength and direction, continually changing over time.Rate this question:
- 28.
Three requirements for induction are a ____, a ____, and ____.
Correct Answer
magnetic field, conductor, motionExplanation
Induction is a process where a changing magnetic field induces an electric current in a conductor. The three requirements for induction are a magnetic field, a conductor, and motion. The magnetic field is necessary to create the changing magnetic flux, the conductor allows the flow of electrons, and the motion is required to change the magnetic field. Without any one of these three components, induction cannot occur.Rate this question:
- 29.
Moving a conductor through a magnetic field induces a ____ and a ____ into that conductor.
Correct Answer
voltage, currentExplanation
When a conductor is moved through a magnetic field, the changing magnetic field induces a voltage in the conductor. This voltage, in turn, causes a flow of electric charges, creating an electric current. This phenomenon is known as electromagnetic induction and is the basis for many electrical devices such as generators and transformers.Rate this question:
- 30.
Mutual induction is the process of ____ a current in a conductor, as the direct result of ____ in another.
Correct Answer
inducing, currentExplanation
Mutual induction is the process by which a current is induced in a conductor as a direct result of the presence of another current. When a changing current flows through one conductor, it creates a changing magnetic field around it. This changing magnetic field then induces a current in a nearby conductor, resulting in mutual induction. Therefore, the correct answer is "inducing, current."Rate this question:
- 31.
Define inductance.
Correct Answer
The ability to store energy in a magnetic field.Explanation
The answer is a concise and accurate definition of inductance. Inductance refers to the ability of a circuit or device to store energy in a magnetic field. When a current flows through a coil or an inductor, a magnetic field is created, and this magnetic field stores energy. This stored energy can be released back into the circuit when the current changes, such as during the switch-off of a circuit or the change in direction of the current. In summary, inductance is the capacity of a circuit or device to store energy in a magnetic field.Rate this question:
- 32.
In the modern world, most power is generated by ____ machines.
Correct Answer
ACExplanation
In the modern world, most power is generated by AC machines. AC stands for alternating current, which is the type of electrical current commonly used for power generation and distribution. AC machines, such as generators and transformers, are designed to convert mechanical energy into electrical energy and vice versa. They play a crucial role in generating electricity for various applications, including powering homes, industries, and transportation systems. AC machines are preferred over DC (direct current) machines for power generation due to their ability to be easily transmitted over long distances and their efficiency in converting energy.Rate this question:
- 33.
The U.S. consumes ____ % of the world's power.
Correct Answer
25Explanation
The U.S. consumes 25% of the world's power. This means that out of the total power consumed globally, 25% is consumed by the United States. This indicates that the U.S. has a significant share in global power consumption, highlighting its large energy needs and usage compared to other countries.Rate this question:
- 34.
Steam turbines are powered by energy types like ____, ____, ____, ____, and ____.
Correct Answer
natural gas, nuclear power, coal, oil, hydropowerExplanation
Steam turbines are powered by various energy sources such as natural gas, nuclear power, coal, oil, and hydropower. These energy sources are used to generate steam, which in turn drives the turbine blades and produces mechanical energy. Natural gas, nuclear power, coal, and oil are commonly used in thermal power plants to heat water and produce steam. Hydropower, on the other hand, utilizes the kinetic energy of flowing or falling water to generate steam and power the turbine.Rate this question:
- 35.
____ and ____ are found in AC equipment.
Correct Answer
rotors, statorsExplanation
Rotors and stators are commonly found in AC equipment. Rotors are the rotating part of the AC equipment, while stators are the stationary part. Together, they work to convert electrical energy into mechanical energy in AC machines such as motors and generators. The rotor rotates within the stator, creating a magnetic field that interacts with the stator's magnetic field, resulting in the generation of mechanical energy. Therefore, both rotors and stators are essential components in AC equipment.Rate this question:
- 36.
The number of poles and rotor speed determine the ____ of an alternator.
Correct Answer
frequencyExplanation
The number of poles and rotor speed determine the frequency of an alternator. The frequency refers to the number of complete cycles of alternating current produced by the alternator per second. The number of poles in the alternator's design and the speed at which the rotor spins directly affect the frequency of the generated electrical output. As the rotor speed increases or the number of poles changes, the frequency of the alternator's output also changes accordingly.Rate this question:
- 37.
The ____ controls the output voltage of an alternator.
Correct Answer
regulatorExplanation
The regulator controls the output voltage of an alternator. It is responsible for maintaining a steady and appropriate voltage level to ensure that the electrical system of a vehicle or any other device is functioning properly. By monitoring and adjusting the voltage, the regulator prevents overcharging or undercharging of the battery and protects the electrical components from damage. Without a regulator, the alternator could potentially produce excessive voltage, leading to equipment failure or even fire hazards.Rate this question:
- 38.
List some of the test instruments that a technician may use to check a motor.
Correct Answer
multimeter, clamp on ammeter, Megger, turn to turn testerExplanation
A technician may use a multimeter to measure voltage, current, and resistance in a motor. A clamp on ammeter can be used to measure the current flowing through a motor without disconnecting any wires. A Megger is used to test the insulation resistance of the motor windings. Lastly, a turn to turn tester is used to check for shorted or open windings in the motor. These test instruments help the technician diagnose and troubleshoot any issues with the motor.Rate this question:
- 39.
If a single phase motor fails to start and makes a substantial hum, either the _____, the ____ winding, or the____ switch has a problem.
Correct Answer
capacitor, start, centrifugalExplanation
If a single phase motor fails to start and makes a substantial hum, it indicates that either the capacitor, the start winding, or the centrifugal switch has a problem. The capacitor is responsible for providing the initial boost of power to start the motor, so if it is faulty or damaged, the motor will not be able to start properly. The start winding is another component that helps in initiating the motor's rotation, and if it is defective, the motor may fail to start. The centrifugal switch is responsible for disconnecting the start winding after the motor reaches a certain speed, and if it malfunctions, it can prevent the motor from starting.Rate this question:
- 40.
Using a voltmeter, check not only for ____ voltage, but also for ____ voltages on the line.
Correct Answer
proper, unbalancedExplanation
When using a voltmeter, it is important to check for proper voltage, which ensures that the line is functioning correctly. Additionally, it is necessary to check for unbalanced voltages on the line, as this can indicate a problem with the electrical system. By checking both proper voltage and unbalanced voltages, one can ensure the safe and efficient operation of the line.Rate this question:
- 41.
Some ambient conditions that are worthy of consideration are ____, ____, ____ environment, ____, and ____.
Correct Answer
temperature, dust, corrosive, moisture, hazardous conditionsExplanation
This question is asking for the ambient conditions that should be taken into consideration. The correct answer includes temperature, dust, corrosive, moisture, and hazardous conditions. These factors are important to consider because they can affect the performance, safety, and longevity of various systems and equipment. Temperature extremes can cause overheating or freezing, dust can clog components and impair functionality, corrosive environments can lead to rust and degradation, moisture can cause damage and electrical issues, and hazardous conditions can pose risks to both equipment and personnel.Rate this question:
- 42.
In selecting the overloads, the correct procedure involves determining size of ____, ____, ____ time, and ____ cycle.
Correct Answer
enclosure, type of load, acceleration, dutyExplanation
The correct procedure for selecting the overloads involves determining the size of the enclosure, the type of load, the acceleration, and the duty cycle. These factors are important in order to ensure that the overloads are properly matched to the specific requirements of the system. The size of the enclosure is important to ensure that the overloads fit properly and can be installed correctly. The type of load is important because different types of loads have different characteristics and require different levels of protection. Acceleration is important to consider because it affects the amount of stress and strain that the overloads will experience. Finally, the duty cycle is important to consider because it determines how frequently and for how long the overloads will be operating.Rate this question:
- 43.
When installing offset drives, three types of alignments are responsible for long belt life. The first is the ____ adjustment, ____ adjustment, and ____ toe.
Correct Answer
offset, angular, pigeonExplanation
The correct answer is offset, angular, pigeon. When installing offset drives, these three types of alignments are crucial for ensuring the longevity of the belt. The offset adjustment refers to aligning the pulleys so that they are parallel to each other, preventing any lateral movement of the belt. The angular adjustment involves aligning the pulleys so that they are perpendicular to the belt's direction of travel, ensuring smooth and efficient power transmission. Lastly, the pigeon toe adjustment refers to aligning the pulleys so that they are parallel to each other in the vertical plane, preventing any twisting or misalignment of the belt.Rate this question:
- 44.
The first step in any motor intallation should be to ____.
Correct Answer
read the nameplate and check information against the conditions of the environment.Explanation
The first step in any motor installation should be to read the nameplate and check information against the conditions of the environment. This is important because the nameplate provides crucial information about the motor, such as its voltage, current, power rating, and operating conditions. By reading the nameplate and comparing it with the environmental conditions, one can ensure that the motor is suitable for the intended application and avoid any potential issues or damage.Rate this question:
- 45.
What do DC motors have a that AC motors do not? ____, ____, ____, ____, and a ____.
Correct Answer
Explanation
DC motors have a commutator, brushes, armature windings, permanent magnets, and a split-ring commutator that allows for the conversion of electrical energy into mechanical energy.Rate this question:
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