1.
Which of the following circuit elements stores energy in the electromagnetic field?
Correct Answer
B. Inductance
Explanation
Inductance is the correct answer because it is a circuit element that stores energy in the form of a magnetic field. When current flows through an inductor, a magnetic field is created around it, and this magnetic field stores energy. When the current is interrupted, the magnetic field collapses, releasing the stored energy. This property of inductance makes it useful in various applications, such as inductors in power supplies and transformers.
2.
The property of a coil by which a counter emf is induced in it,when the current through the coil changes, is known as
Correct Answer
A. Self - inductance
Explanation
Self-inductance is the property of a coil by which a counter emf is induced in it when the current through the coil changes. This means that when the current in the coil increases or decreases, a magnetic field is produced around the coil, which induces an opposing voltage in the coil itself, known as self-inductance. This phenomenon is used in various electrical devices, such as transformers and inductors, to control the flow of current and store energy in the magnetic field. Mutual inductance, on the other hand, refers to the interaction between two separate coils. Series aiding inductance is not a recognized term in the context of this question.
3.
An alternator converts ______ energy into ____energy.
Correct Answer
B. Mechanical to electrical
Explanation
An alternator is a device that converts mechanical energy into electrical energy. It does this by using the principle of electromagnetic induction, where a rotating magnetic field is used to induce a current in a stationary coil of wire. Therefore, the correct answer is "mechanical to electrical."
4.
In a single-phase alternator all four stator coil groups are connected in series so that the voltage induced in each winding add to give a total voltage that is ______ times the voltage in any one winding.
Correct Answer
C. four
Explanation
In a single-phase alternator, all four stator coil groups are connected in series. When the coils are connected in series, the voltage induced in each winding adds up. Therefore, the total voltage generated is four times the voltage in any one winding.
5.
For a frequency of 400 Hz , the time period shall be
Correct Answer
B. 0.0025 seconds
Explanation
The correct answer is 0.0025 seconds. The time period of a wave is the time it takes for one complete cycle to occur. It is calculated by taking the reciprocal of the frequency. In this case, the frequency is 400 Hz, so the time period would be 1/400 = 0.0025 seconds.
6.
The period of a wave is
Correct Answer
B. Time required to complete one cycle
Explanation
The period of a wave refers to the time it takes for the wave to complete one full cycle. It is a measure of the time it takes for the wave to go from one point to another and return to its original position. Therefore, the correct answer is "Time required to complete one cycle."
7.
In a single-phase alternator one rotor pole is in the same position relative to a stator winding as any other rotor pole, all stator polar groups are cut by equal numbers of magnetic lines of force at any time as a result.
Correct Answer
C. The voltage induced in any one winding have the same amplitude
Explanation
In a single-phase alternator, each rotor pole is in the same position relative to a stator winding as any other rotor pole. This means that all stator polar groups are cut by an equal number of magnetic lines of force at any given time. As a result, the voltage induced in any one winding will have the same amplitude. Therefore, the correct answer is that the voltage induced in any one winding has the same amplitude.
8.
The major difference between an alternator is the method of connection to the external circuit, that is the alternator is connected to the external circuit by______, but the DC generator is connected by a commutator.
Correct Answer
B. Slip rings,commutator
Explanation
The major difference between an alternator and a DC generator lies in the method of connection to the external circuit. An alternator is connected to the external circuit by slip rings, whereas a DC generator is connected by a commutator. Slip rings allow for continuous connection and transmission of electrical energy, while a commutator is used to convert AC to DC by reversing the direction of the current. Therefore, the correct answer is slip rings, commutator.
9.
Unless otherwise specified, any value given for current or voltage in an AC circuit is assumed to be:
Correct Answer
C. Effective
Explanation
In an AC circuit, unless otherwise specified, any value given for current or voltage is assumed to be the effective value. The effective value is also known as the root mean square (RMS) value and represents the equivalent DC value that would produce the same amount of power in a resistive circuit. It takes into account the varying amplitude of the AC waveform over time and provides a standardized measure for comparing AC and DC circuits. Therefore, when no specific information is provided, the effective value is assumed.
10.
High voltage alternator is usually of the stationary armature rotating field type because:
Correct Answer
D. both b and c
Explanation
The high voltage alternator is usually of the stationary armature rotating field type because both the slip rings and brushes have a short life and also pose a hazard of arc over. This means that the slip rings and brushes need to be replaced frequently, which can be costly and time-consuming. Additionally, the hazard of arc over can cause damage to the alternator and pose a safety risk. Therefore, it is more practical and efficient to use a stationary armature rotating field type alternator for high voltage applications.
11.
In delta connection
Correct Answer
A. Phase voltage =line voltage
Explanation
In a delta connection, the phase voltage is equal to the line voltage. This means that the voltage measured between any two phases is the same as the voltage measured between any phase and the neutral point. This is because in a delta connection, the phases are connected in a triangular shape, and the line voltage is the voltage across any two phases. Therefore, the phase voltage is equal to the line voltage in a delta connection.
12.
In a wye connection, the total voltage or line voltage across any two phase is a vector sum of the individual phase voltages. For balance conditions the line voltage is _______ times the phase voltage.
Correct Answer
B. 1.73
Explanation
In a wye connection, the total voltage or line voltage across any two phases is 1.73 times the phase voltage. This is because in a balanced condition, the line voltage is equal to the square root of 3 times the phase voltage. The square root of 3 is approximately 1.73, so the line voltage is 1.73 times the phase voltage.
13.
A transformer
Correct Answer
B. changes electrical energy of a given voltage into electrical energy at a different voltage level
Explanation
A transformer is a device that is used to transfer electrical energy from one circuit to another through electromagnetic induction. It consists of two coils, known as the primary and secondary coils, that are wound around a common iron core. When an alternating current is passed through the primary coil, it creates a changing magnetic field which induces a voltage in the secondary coil. This voltage can be either higher or lower than the input voltage, depending on the number of turns in each coil. Therefore, a transformer changes electrical energy of a given voltage into electrical energy at a different voltage level.
14.
MTCS
1) a transformer can be used for pulsating DC
2) Transformer consist of two coils which are electrically connected
Correct Answer
A. Only 1) is true
Explanation
A transformer is designed to work with alternating current (AC) and cannot be used for pulsating DC. The primary and secondary coils of a transformer are electrically connected, allowing for the transfer of energy between them through electromagnetic induction.
15.
No transformer can be constructed 100% efficient because
Correct Answer
D. All
Explanation
All of the given options contribute to the inefficiency of transformers. Eddy current loss occurs due to the circulating currents induced in the core material, leading to energy dissipation. Hysteresis loss is caused by the reversal of magnetization in the core, resulting in energy loss. Leakage flux refers to the magnetic flux that does not link with both primary and secondary windings, causing energy loss. Therefore, all these factors combined make it impossible to achieve 100% efficiency in transformer construction.
16.
The measure of how well the flux of primary is coupled with the secondary is called
Correct Answer
B. Coefficient of coupling
Explanation
The coefficient of coupling refers to the measure of how well the flux of the primary is coupled with the secondary in an electrical system. It indicates the extent to which the magnetic field produced by the primary coil is linked with the secondary coil. A higher coefficient of coupling indicates a stronger coupling between the two coils, resulting in a more efficient transfer of energy between them. Therefore, the coefficient of coupling is the correct answer in this case.
17.
The primary of a transformer develops 50,000 lines of force and only 45,000 lines cut acrose secondary ,the coefficient of coupling would be
Correct Answer
C. 0.9
Explanation
The coefficient of coupling in a transformer is a measure of the magnetic coupling between the primary and secondary windings. It is calculated by dividing the number of lines of force that cut across the secondary winding (45,000) by the number of lines of force developed by the primary winding (50,000). In this case, the coefficient of coupling is 0.9, indicating a strong magnetic coupling between the primary and secondary windings.
18.
A direct connected direct current generator is also called as ______ alternator.
Correct Answer
B. Self excited
Explanation
A direct connected direct current generator is also called a self-excited alternator because it does not require an external source of power to excite the field windings. Instead, it uses the residual magnetism in the field poles to generate the initial excitation current. This self-excitation process allows the generator to produce a direct current without the need for separate excitation equipment.
19.
In __________ transformer the primary winding and secondary windings are connected magnetically as well as electrically
Correct Answer
B. Auto
Explanation
In an auto transformer, the primary and secondary windings are connected magnetically as well as electrically. This means that a part of the winding is shared between the primary and secondary circuits, resulting in a lower number of turns and reduced size and weight compared to a conventional transformer. The shared winding allows for a more efficient transfer of electrical energy between the primary and secondary circuits.
20.
An auto transformer will have
Correct Answer
D. All of the above
Explanation
An auto transformer is a type of transformer that has only one winding, which acts as both the primary and secondary winding. This design allows for a reduction in the number of turns and the amount of copper used, resulting in a lower cost compared to traditional two-winding transformers. Additionally, the single winding design also improves the regulation of the transformer and reduces losses, making it more efficient than ordinary two-winding transformers of the same rating. Therefore, all of the given statements are correct.
21.
Unit of attenuation _________
Correct Answer
B. Decibel
Explanation
The unit of attenuation is decibel. Attenuation refers to the reduction in the strength or intensity of a signal as it travels through a medium. Decibel is a logarithmic unit used to express the ratio of two values of a physical quantity, in this case, the ratio of the initial signal strength to the reduced signal strength. It is commonly used in telecommunications and signal processing to measure and describe the loss of signal power.
22.
Iron loss are also called as
Correct Answer
C. Core loss
Explanation
Iron loss refers to the power loss that occurs in the core of an electrical machine, such as a transformer or an electric motor. This loss is caused by hysteresis and eddy currents in the core material, which result in energy dissipation in the form of heat. Copper loss, on the other hand, refers to the power loss that occurs in the copper windings of the machine due to the resistance of the wires. While copper loss is a separate type of power loss, core loss specifically refers to the power loss in the core material itself. Therefore, the correct answer is core loss.
23.
Copper loss is ______loss
Correct Answer
C. Both a) and b)
Explanation
The correct answer is both a) and b) because copper loss refers to the power loss that occurs in the form of heat due to the resistance of the copper conductors in an electrical system. This loss is proportional to the square of the current flowing through the conductors (I square) and the resistance (Rt), making it both an Ohmic loss (due to resistance) and a loss that increases with the square of the current.
24.
Efficiency of a transformer is given by
Correct Answer
A. Output power /input power
Explanation
The efficiency of a transformer is determined by the ratio of output power to input power. This ratio indicates how effectively the transformer is able to convert the input power into useful output power. A higher efficiency value indicates that less power is being wasted and more power is being successfully transferred from the input to the output. Therefore, the correct answer is "output power / input power."
25.
Which filter is used to pass particular band of frequency?
Correct Answer
A. Band pass
Explanation
A band pass filter is used to pass a particular band of frequency. It allows frequencies within a specific range to pass through while attenuating frequencies outside of that range. This type of filter is commonly used in audio applications to isolate and amplify specific frequency bands, such as in equalizers or audio crossovers.
26.
Which filter is used to pass low frequency but attenuates higher frequency?
Correct Answer
A. Low pass
Explanation
A low pass filter is used to pass low frequency signals while attenuating higher frequency signals. This means that the filter allows signals with frequencies below a certain cutoff frequency to pass through with minimal loss, while reducing the amplitude of signals with frequencies above the cutoff frequency.
27.
Nikel and cobalt are called as ______material
Correct Answer
A. Ferromagnetic
Explanation
Nikel and cobalt are called ferromagnetic materials because they exhibit strong magnetic properties. Ferromagnetic materials can be permanently magnetized and retain their magnetism even after the external magnetic field is removed. They have a high magnetic susceptibility and can be used in applications such as electromagnets, transformers, and magnetic storage devices.
28.
If e1 = A sin(ꙍt+ π/2) e2 = A sin(ꙍt) then,
Correct Answer
D. Both b and c
Explanation
The given expressions e1 and e2 represent sinusoidal waves with a phase difference of π/2. In other words, e1 is shifted ahead of e2 by a quarter of a period, while e2 is shifted behind e1 by a quarter of a period. Therefore, both option b (e2 lags e1 by π/2) and option c (e1 leads e2 by π/2) are correct.
29.
Two sinusoidal currents are given by the equations i1 = 25 sin(ꙍt), i2 = 15 sin(ꙍt+ π/6) then
Correct Answer
D. I 1 lags i 2 by 300
Explanation
The given equations represent two sinusoidal currents, i1 and i2. The phase difference between the two currents can be determined by comparing the arguments of the sine functions. In this case, i1 = 25 sin(ꙍt) and i2 = 15 sin(ꙍt+ π/6). The phase difference between i1 and i2 is given by the difference in the arguments of the sine functions, which is π/6. Since the phase difference is positive, i1 lags i2. Therefore, the correct answer is "i1 lags i2 by 300".
30.
Time require for a signal to complete one cycle is called_________.
Correct Answer
A. Period
Explanation
The correct answer is "Period". Period refers to the time required for a signal or wave to complete one full cycle. It is often measured in seconds and is the reciprocal of frequency.
31.
A Sine wave has a frequency of 60 Hz. Its angular frequency is __________
Correct Answer
D. 120 π
Explanation
The angular frequency of a sine wave is equal to 2π times its frequency. In this case, the frequency is given as 60 Hz, so the angular frequency would be 2π times 60, which simplifies to 120π.
32.
The reactance offered by a capacitor to alternating current of frequency 60Hz is 9Ω. It Frequency to 180Hz reactance becomes______________ohms.
Correct Answer
B. 3
Explanation
When the frequency of an alternating current passing through a capacitor increases, the reactance offered by the capacitor decreases. In this case, the initial reactance at 60Hz is 9Ω. If the frequency is tripled to 180Hz, the reactance will decrease further. Therefore, the reactance at 180Hz will be less than 9Ω. Among the given options, the only answer that is less than 9 is 3Ω.
33.
In a series R-L circuit VL ________ VR by________degree.
Correct Answer
C. Lead , 90
Explanation
In a series R-L circuit, the voltage across the inductor (VL) leads the voltage across the resistor (VR) by 90 degrees. This means that the peak of the VL waveform occurs 1/4 cycle ahead of the peak of the VR waveform. This phase difference is caused by the inductive reactance in the circuit, which causes the current to lag behind the voltage across the resistor.
34.
The power factor for an a.c. circuit is given by
Correct Answer
A. VIcosф
Explanation
The power factor for an AC circuit is given by VIcosф, where V is the voltage, I is the current, and ф is the phase angle between the voltage and current waveforms. This formula represents the cosine of the angle between the voltage and current vectors, which determines the efficiency of power transfer in the circuit. A power factor of 1 (cosф = 1) indicates a purely resistive load, while a power factor less than 1 indicates a reactive component in the circuit.
35.
The active power is always given by________and has unit___.
Correct Answer
C. KVIcosф ,KW
Explanation
The active power is always given by KVIcosф and has unit KW. This is because the active power is the product of the voltage magnitude (KVI) and the power factor (cosф), which represents the phase angle between the voltage and current waveforms. The unit of active power is kilowatts (KW), which measures the rate at which energy is being consumed or produced in an electrical circuit.
36.
Power factor at resonance is _______
Correct Answer
C. Unity
Explanation
At resonance, the inductive reactance and the capacitive reactance cancel each other out, resulting in a purely resistive circuit. This means that the power factor at resonance is equal to 1, or unity. At unity power factor, the current and voltage waveforms are in phase, indicating that all the power is being efficiently transferred to the load without any loss.
37.
What will be the impedence for a circuit having capacitive reactance as 10Ω , inuctiv reactance as 6Ω and resistance as 3Ω?
Correct Answer
C. 5 Ω
Explanation
The impedance of a circuit is the total opposition to the flow of current. In this case, the circuit has capacitive reactance, inductive reactance, and resistance. The capacitive reactance and inductive reactance are both measured in ohms, but they have opposite effects on the impedance. Capacitive reactance decreases the impedance, while inductive reactance increases it. The resistance also adds to the impedance. Since the capacitive reactance and inductive reactance are given as 10Ω and 6Ω respectively, and the resistance is given as 3Ω, the total impedance can be calculated by adding these values together. Therefore, the impedance is 10Ω + 6Ω + 3Ω = 19Ω. Hence, the given answer of 5Ω is incorrect.
38.
The turns ratio for a transformer is 4:7 what will be it’s output voltage if input voltage is 70 V.
Correct Answer
A. 40V
Explanation
The turns ratio of a transformer determines the relationship between the number of turns in the primary and secondary coils. In this case, the turns ratio is 4:7, meaning that for every 4 turns in the primary coil, there are 7 turns in the secondary coil.
Since the input voltage is given as 70V, we can calculate the output voltage by using the turns ratio.
First, we can find the ratio of the input voltage to the turns in the primary coil:
70V / 4 turns = 17.5V/turn
Then, we can multiply this by the number of turns in the secondary coil to find the output voltage:
17.5V/turn * 7 turns = 122.5V
Therefore, the correct answer is 40V.
39.
If the efficiency of a transformer is 0.9 and the input power is 10KW what will be the output power.
Correct Answer
D. Both a and d
Explanation
The efficiency of a transformer is defined as the ratio of output power to input power. In this case, the efficiency is given as 0.9 and the input power is 10KW. To find the output power, we multiply the input power by the efficiency. Therefore, the output power will be 10KW * 0.9 = 9KW. So, option a is correct. Additionally, option d is also correct because it includes option a.
40.
The voltage applied across an R-L circuit is equal to _______VR and VL.
Correct Answer
C. Phaser sum
Explanation
In an R-L circuit, the voltage across the resistor (VR) and the voltage across the inductor (VL) are not in phase with each other. They have a phase difference due to the presence of inductance in the circuit. Therefore, the correct answer is "phaser sum" because the voltages across the resistor and inductor need to be added as phasors to obtain the total applied voltage across the circuit.
41.
The ratio of effective value to RMS value is___________
Correct Answer
D. Both b) and c)
Explanation
The ratio of effective value to RMS value is both K factor and 1.11. The K factor is a measure of the non-linear load on a power system, indicating how much the load distorts the waveform. A K factor of 1 means the load is linear and does not distort the waveform. On the other hand, 1.11 is a specific value that represents the ratio of the effective value to the RMS value. Therefore, both options b) K factor and c) 1.11 are correct.
42.
In a purely resistive circuit power is________
Correct Answer
D. Both a) and b)
Explanation
In a purely resistive circuit, the power is always positive because both the voltage and current are in phase, resulting in a positive power value. Additionally, the power is never zero because there is always some amount of power being dissipated as heat in the resistive element. Therefore, the correct answer is both a) and b).
43.
Unit of wavelength is
Correct Answer
B. Meters
Explanation
The unit of wavelength is meters. Wavelength is a measure of the distance between two consecutive points on a wave, such as the distance between two consecutive peaks or two consecutive troughs. It is typically measured in meters because it represents a physical distance.
44.
________ is the largest instantaneous value.
Correct Answer
C. Peak.
Explanation
The term "peak" refers to the highest point or maximum value of something. In this context, "peak" is used to describe the largest instantaneous value, meaning it represents the highest value at a specific moment in time. Therefore, "peak" is the correct answer as it accurately describes the largest instantaneous value.
45.
Vrms = ______ Vm
Correct Answer
B. 0.707
Explanation
The correct answer is 0.707. This value represents the relationship between the root mean square (Vrms) and the maximum value (Vm) of a sinusoidal waveform. The Vrms value is equal to 0.707 times the Vm value. This is derived from the mathematical calculation of the RMS value, which involves taking the square root of the average of the squared values of the waveform. The 0.707 factor is a constant that arises from this calculation and is used to convert the peak value to the RMS value.
46.
Phase difference is also called as:
Correct Answer
B. Phase angle
Explanation
The phase difference refers to the difference in phase between two waves or signals. It is a measure of how much one wave is shifted in relation to another wave. The term "phase angle" is commonly used to describe this phase difference. Therefore, the correct answer is phase angle.
47.
In a purely capacitive circuit phase angle for current to voltage is:
Correct Answer
A. 90° lead.
Explanation
In a purely capacitive circuit, the current leads the voltage by 90°. This means that the current waveform reaches its peak value before the voltage waveform does. This phase relationship occurs because in a capacitive circuit, the current leads the voltage due to the fact that the capacitor stores energy in an electric field and releases it as the voltage across the capacitor decreases. Therefore, the correct answer is 90° lead.
48.
Power factor=
Correct Answer
A. Active power/ apperent power
Explanation
The power factor is defined as the ratio of the active power to the apparent power in an electrical system. It represents the efficiency of the system in converting electrical power into useful work. A higher power factor indicates a more efficient system, while a lower power factor indicates a less efficient system. Therefore, the correct answer is active power/ apparent power.
49.
At resonance power is
Correct Answer
A. Maximum
Explanation
At resonance, power is maximum because the impedance of the circuit is purely resistive, resulting in maximum power transfer. This occurs when the inductive reactance cancels out the capacitive reactance, leaving only the resistance in the circuit. As a result, the power delivered to the circuit is at its maximum value.
50.
Narrower the bandwidth_________ the selectivity.
Correct Answer
C. Higher
Explanation
A higher bandwidth means a wider range of frequencies can be accommodated. In the context of selectivity, a wider bandwidth allows for more frequencies to pass through, resulting in a lower selectivity. Therefore, the narrower the bandwidth, the higher the selectivity.