The PYQ practice room
GATE EE 2015 Set 1
All 65 solved GATE EE 2015 Set 1 questions in exam order. Open a question, commit to an answer, and learn from the step-by-step solution. One question at a time.
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65
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100
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General Aptitude (GA)
101
Q1MCQ1 markEasyDidn't you buy ________ when you went shopping?Think it through. Then check your answer.Question
Didn't you buy ________ when you went shopping?Correct answer
(A) any paper
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The blank needs a word that asks whether some quantity of paper was bought. In questions (including negative questions such as "Didn't you…?"), the usual determiner for this is any, so the sentence reads "Didn't you buy any paper…?"- much paper: "much" asks about a large amount. It does not fit a plain question about whether any paper was bought at all.
- no paper: this gives a double negative with "didn't".
- a few paper: "a few" goes only with countable plural nouns, and "paper" (the material) is uncountable.
2
Q2MCQ1 markEasyWhich of the following options is the closest in meaning to the sentence below? She enjoyed herself immensely at the party.Think it through. Then check your answer.Question
Which of the following options is the closest in meaning to the sentence below?She enjoyed herself immensely at the party.Correct answer
(C) She had a terrific time at the party
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'Terrific' is a synonym for 'extremely good' or 'immense enjoyment', which matches the meaning of 'enjoyed herself immensely'. 'Terrible', 'horrible', and 'terrifying' have negative meanings.3
Q3MCQ1 markMediumWhich one of the following combinations is incorrect?Think it through. Then check your answer.Question
Which one of the following combinations is incorrect?Correct answer
(B) Wheedle - Roundabout
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The pairs in A, C, and D are synonyms. 'Wheedle' means to coax or persuade through flattery, whereas 'roundabout' means indirect. Thus, the combination in B is incorrect.4
Q4MCQ1 markEasyBased on the given statements, select the most appropriate option to solve the given question. If two floors in a certain building are 9 feet apart, how many steps are there in a…Think it through. Then check your answer.Question
Based on the given statements, select the most appropriate option to solve the given question.
If two floors in a certain building are 9 feet apart, how many steps are there in a set of stairs that extends from the first floor to the second floor of the building?
Statements:
(I) Each step is 3/4 foot high.
(II) Each step is 1 foot wide.Correct answer
(A) Statement I alone is sufficient, but statement II alone is not sufficient.
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To find the number of steps, we need to know the total vertical distance between the floors and the height of each step.Given:
Total vertical distance between two floors = 9 feet.Statement (I): Each step is 3/4 foot high.
From this statement, we can calculate the number of steps: Number of steps = steps.
So, Statement I alone is sufficient.Statement (II): Each step is 1 foot wide.
This statement gives information about the width of the step, which is irrelevant to the number of steps required to cover a vertical distance. So, Statement II alone is not sufficient.Therefore, Statement I alone is sufficient, but Statement II alone is not sufficient.The correct option is (A).5
Q5MCQ1 markEasyGiven Set A = and Set B = , two numbers are randomly selected, one from each set. What is the probability that the sum of the two numbers…Think it through. Then check your answer.Question
Given Set A = and Set B = , two numbers are randomly selected, one from each set. What is the probability that the sum of the two numbers equals 16?Correct answer
(A) 0.20
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Let be the number of elements in Set A, and be the number of elements in Set B.
Set A = , so .
Set B = , so .When two numbers are randomly selected, one from each set, the total number of possible pairs is .We need to find pairs where , , such that .
Let's list the possible pairs:
If , then . is a valid pair since .
If , then . is a valid pair since .
If , then . is a valid pair since .
If , then . is a valid pair since .The favorable outcomes are 4 pairs: .Number of favorable outcomes = 4.
Total number of possible outcomes = 20.Probability = .The correct option is (A).6
Q6MCQ2 marksEasySelect the alternative meaning of the underlined part of the sentence. The chain snatchers took to their heels when the police party arrived.Think it through. Then check your answer.Question
Select the alternative meaning of the underlined part of the sentence.
The chain snatchers took to their heels when the police party arrived.Correct answer
(C) took to flight
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The idiom "took to their heels" means to run away or flee, typically in a hurry or to escape from something.Let's analyze the given options:
(A) "took shelter in a thick jungle" implies hiding, not necessarily running away.
(B) "open indiscriminate fire" means to start shooting randomly, which is not related to the idiom.
(C) "took to flight" means to flee or run away, which perfectly matches the meaning of "took to their heels".
(D) "unconditionally surrendered" means to give up without any demands, which is the opposite of running away.Therefore, the closest meaning to "took to their heels" is "took to flight".The correct option is (C).7
Q7MCQ2 marksEasyThe given statement is followed by some courses of action. Assuming the statement to be true, decide the correct option. Statement: There has been a significant drop in the…Think it through. Then check your answer.Question
The given statement is followed by some courses of action. Assuming the statement to be true, decide the correct option.Statement:There has been a significant drop in the water level in the lakes supplying water to the city.Course of action:(I) The water supply authority should impose a partial cut in supply to tackle the situation.
(II) The government should appeal to all the residents through mass media for minimal use of water.
(III) The government should ban the water supply in lower areas.Correct answer
(A) Statements I and II follow.
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Course of action (I) is a logical and immediate step to conserve the remaining water supply. Course of action (II) is a proactive measure to reduce overall demand through public cooperation. Course of action (III) is discriminatory and not a standard or fair administrative response to a general water shortage. Therefore, only statements I and II follow.8
Q8NAT2 marksMediumThe pie chart below has the breakup of the number of students from different departments in an engineering college for the year 2012. The proportion of male to female students in…9
Q9MCQ2 marksMediumThe probabilities that a student passes in Mathematics, Physics and Chemistry are , , and respectively. Of these subjects, the student has 75% chance of passing in at…Think it through. Then check your answer.Question
The probabilities that a student passes in Mathematics, Physics and Chemistry are , , and respectively. Of these subjects, the student has 75% chance of passing in at least one, a 50% chance of passing in at least two and a 40% chance of passing in exactly two. Following relations are drawn in , , :(I)
(II)
(III)Correct answer
(D) Relations I and III are true.
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Let be the events of passing Mathematics, Physics and Chemistry, with , , . Write and .- At least one: .
- At least two: (each pairwise term counts the all-three outcome once, so three counts are reduced to one).
- Exactly two: .
10
Q10MCQ2 marksEasyThe number of students in a class who have answered correctly, wrongly, or not attempted each question in an exam, are listed in the table below. The marks for each question are…Think it through. Then check your answer.Question
The number of students in a class who have answered correctly, wrongly, or not attempted each question in an exam, are listed in the table below. The marks for each question are also listed. There is no negative or partial marking.What is the average of the marks obtained by the class in the examination?Q No. Marks Answered Correctly Answered Wrongly Not Attempted 1 2 21 17 6 2 3 15 27 2 3 1 11 29 4 4 2 23 18 3 5 5 31 12 1 Correct answer
(C) 6.795
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1.First, determine the total number of students in the class. Summing the columns for any question (Correct + Wrong + Not Attempted) gives: students.2.Calculate the total marks obtained by the entire class by summing the marks for each question multiplied by the number of correct answers:- Q1:
- Q2:
- Q3:
- Q4:
- Q5:
3.Calculate the average marks: .Rounding to three decimal places, we get 6.795.
Electrical Engineering
5511
Q11NAT1 markMediumA random variable has probability density function as given below: If the…Think it through. Then check your answer.Question
A random variable has probability density function as given below:If the expected value , then is ___________.Correct answer
0.25 to 0.25
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1.Use the normalization property of PDF: .(Equation 1).2.Use the expected value formula: .(Equation 2).3.Solve the system of equations:From (1), . Substitute into (2):
.
Then .
So, for .4.Calculate :.12
Q12MCQ1 markEasyIf a continuous function does not have a root in the interval , then which one of the following statements is TRUE?Think it through. Then check your answer.Question
If a continuous function does not have a root in the interval , then which one of the following statements is TRUE?Correct answer
(C) f(a) · f(b) 0
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By the Intermediate Value Theorem, if a continuous had (opposite signs at the ends), it would have to cross zero somewhere in . Likewise means or itself is a root.Since has no root in , both cases are impossible (this is the contrapositive of the theorem): and are non-zero and have the same sign. Hencewhich also rules out (D), since is then positive.Answer: (C)13
Q13NAT1 markMediumIf the sum of the diagonal elements of a matrix is , then the maximum possible value of determinant of the matrix is ________.Think it through. Then check your answer.Question
If the sum of the diagonal elements of a matrix is , then the maximum possible value of determinant of the matrix is ________.Correct answer
9 to 9
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Let the matrix be with , and let its eigenvalues be . ThenThe intended setting is a matrix with real eigenvalues (for example a real symmetric matrix). Then giveswith equality when , e.g. .(Without that restriction the determinant has no upper bound: has trace and determinant , with complex eigenvalues. The accepted value therefore rests on the real-eigenvalue reading.)Maximum possible determinant .14
Q14MCQ1 markHardConsider a function , where is the distance from the origin and is the unit vector in the radial direction. The divergence of this…Think it through. Then check your answer.Question
Consider a function , where is the distance from the origin and is the unit vector in the radial direction. The divergence of this function over a sphere of radius , which includes the origin, isCorrect answer
(C) 4π
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The function is given as . According to the properties of the Dirac delta function in three dimensions:The question asks for the divergence 'over a sphere', which implies the volume integral of the divergence over the sphere of radius that includes the origin.Alternatively, using the Gauss Divergence Theorem:For a sphere of radius , the surface element is .15
Q15MCQ1 markEasyWhen the Wheatstone bridge shown in the figure is used to find the value of resistor , the galvanometer indicates zero current when , …Think it through. Then check your answer.Question
When the Wheatstone bridge shown in the figure is used to find the value of resistor , the galvanometer indicates zero current when , and . If is known with tolerance on its nominal value of , what is the range of in Ohms?
Correct answer
(A) [123.50, 136.50]
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For a balanced Wheatstone bridge, the condition is:Given and . The nominal value of is with a tolerance of .Calculating the range for :Thus, the range of is .16
Q16NAT1 markEasyA (0-50 A) moving coil ammeter has a voltage drop of 0.1 V across its terminals at full scale deflection. The external shunt resistance (in milliohms) needed to extend its range…Think it through. Then check your answer.Question
A (0-50 A) moving coil ammeter has a voltage drop of 0.1 V across its terminals at full scale deflection. The external shunt resistance (in milliohms) needed to extend its range to (0 – 500 A) is _________.Correct answer
0.22 to 0.23
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Given:
Full scale meter current, A
Voltage drop at full scale, V
Meter resistance,
Desired full scale current, A
Multiplying factor,
Shunt resistance required,
Thus, the shunt resistance needed is approximately milliohms.17
Q17MCQ1 markEasyOf the four characteristics given below, which are the major requirements for an instrumentation amplifier? P. High common mode rejection ratio Q. High input impedance R. High…Think it through. Then check your answer.Question
Of the four characteristics given below, which are the major requirements for an instrumentation amplifier?P. High common mode rejection ratio
Q. High input impedance
R. High linearity
S. High output impedanceCorrect answer
(A) P, Q and R only
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An instrumentation amplifier is designed to amplify very small differential signals while rejecting large common-mode signals. Its key requirements are:1.High Common Mode Rejection Ratio (CMRR) (P): To reject noise common to both inputs.2.High Input Impedance (Q): To prevent loading of the signal source.3.High Linearity (R): To ensure the output is a faithful reproduction of the input.4.Low Output Impedance: To drive subsequent stages without signal loss. (Characteristic S, high output impedance, is incorrect).Therefore, P, Q, and R are the major requirements.18
Q18NAT1 markMediumIn the following chopper, the duty ratio of switch S is 0.4. If the inductor and capacitor are sufficiently large to ensure continuous inductor current and ripple free capacitor…Think it through. Then check your answer.Question
In the following chopper, the duty ratio of switch S is 0.4. If the inductor and capacitor are sufficiently large to ensure continuous inductor current and ripple free capacitor voltage, the charging current (in Ampere) of the 5 V battery, under steady-state, is_______.
Correct answer
1 to 1
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The given circuit is a step-down (buck) chopper.
Input voltage, V
Duty ratio,
Average output voltage, V
The load consists of a resistor and a battery V in series.
Under steady-state, the average current flowing into the battery is:
A19
Q19NAT1 markMediumA moving average function is given by . If the input is a sinusoidal signal of frequency Hz, then in steady…Think it through. Then check your answer.Question
A moving average function is given by . If the input is a sinusoidal signal of frequency Hz, then in steady state, the output will lag (in degree) by ______.Correct answer
90 to 90
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The transfer function of the moving average filter is given by:For a sinusoidal input with frequency Hz, the angular frequency is:Substituting into the transfer function:Since :The phase angle of the transfer function is , which means the output lags the input by .20
Q20MCQ1 markMediumThe impulse response of a system, , is as shown in Figure (a). What is the maximum value attained by the impulse response of two cascaded blocks of as shown in…Think it through. Then check your answer.Question
The impulse response of a system, , is as shown in Figure (a). What is the maximum value attained by the impulse response of two cascaded blocks of as shown in Figure (b)?
Correct answer
(D) 1
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The impulse response of two cascaded blocks is the convolution of their individual impulse responses.
Given , which is a unit pulse of height 1 from to .
The total impulse response is:The convolution of two identical rectangular pulses of width and height is a triangular pulse of width and peak height .
Here, and , so the peak height is .
The resulting triangular pulse starts at , reaches its maximum value of 1 at , and ends at .
Thus, the maximum value attained is 1.21
Q21NAT1 markMediumConsider a one-turn rectangular loop of wire placed in a uniform magnetic field as shown in the figure. The plane of the loop is perpendicular to the field lines. The resistance…Think it through. Then check your answer.Question
Consider a one-turn rectangular loop of wire placed in a uniform magnetic field as shown in the figure. The plane of the loop is perpendicular to the field lines. The resistance of the loop is , and its inductance is negligible. The magnetic flux density (in Tesla) is a function of time, and is given by , where radian/second. The power absorbed (in Watt) by the loop from the magnetic field is ______.
Correct answer
0.17 to 0.2
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1.Calculate the area of the loop:.2.Find the magnetic flux:Weber.3.Calculate the induced EMF:.
The peak EMF is V.4.Calculate the RMS EMF:V.5.Calculate the power absorbed:W.The calculated value is approximately 0.193 W, which falls within the range 0.17 to 0.2.22
Q22MCQ1 markEasyA steady current is flowing in the direction through each of two infinitely long wires at as shown in the figure. The permeability of the medium is…Think it through. Then check your answer.Question
A steady current is flowing in the direction through each of two infinitely long wires at as shown in the figure. The permeability of the medium is . The -field at is
Correct answer
(A) -(4μ₀ I)/(3π L)z
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The magnetic flux density of an infinitely long straight wire at perpendicular distance iswith direction , where is the current direction and is the unit vector from the wire to the field point.Both wires carry current in the direction, and the field point lies on the side of both wires, so for each:Wire at : distance
Wire at : distance
Total field:This matches option (A).Answer: (A)23
Q23MCQ1 markMediumConsider the circuit shown in the figure. In this circuit , and . The input voltage is sinusoidal with a frequency of 50 Hz, represented…Think it through. Then check your answer.Question
Consider the circuit shown in the figure. In this circuit , and . The input voltage is sinusoidal with a frequency of 50 Hz, represented as a phasor with magnitude and phase angle 0 radian as shown in the figure. The output voltage is represented as a phasor with magnitude and phase angle radian. What is the value of the output phase angle (in radian) relative to the phase angle of the input voltage?
Correct answer
(D) -(π)/(2)
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Let the upper input terminal be at potential and the lower input terminal at (both with respect to ground), so that . Let .Non-inverting input: reaches the terminal through , with to ground:Inverting input: for an ideal op-amp . KCL at the inverting node (current through from equals current through the feedback ):Substituting :With :Since has phase 0, the output phase angle is rad. This matches option (D).Answer: (D)24
Q24NAT1 markMediumIn the given circuit, the silicon transistor has and a collector voltage V. Then the ratio of and is ________. [figure]Think it through. Then check your answer.Question
In the given circuit, the silicon transistor has and a collector voltage V. Then the ratio of and is ________.
Correct answer
100 to 110
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The circuit is a collector-to-base (collector feedback) bias: connects the 15 V supply to the collector, and connects the collector to the base. The emitter is grounded.For a silicon transistor, V.Base current (through ):Current through : it feeds both the collector and :Ratio:Answer: (accepted range 100 to 110)25
Q25MCQ1 markEasyIn the multiplexer, the output is given by . Find the required input ''. [figure]Think it through. Then check your answer.Question
In the multiplexer, the output is given by . Find the required input ''.
Correct answer
(B) 0110
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The output of a multiplexer with select lines and is given by the expression:Given that and , the output becomes:We are given the desired output function as .
By comparing the coefficients of the minterms in both expressions:- For :
- For :
- For :
- For :
26
Q26MCQ1 markMediumConsider a HVDC link which uses thyristor based line-commutated converters as shown in the figure. For a power flow of from System 1 to System 2, the voltages at…Think it through. Then check your answer.Question
Consider a HVDC link which uses thyristor based line-commutated converters as shown in the figure. For a power flow of from System 1 to System 2, the voltages at the two ends, and the current, are given by: and . If the direction of power flow is to be reversed (that is, from System 2 to System 1) without changing the electrical connections, then which one of the following combinations is feasible?
Correct answer
(B) V₁ = -485 kV, V₂ = -500 kV and I = 1.5 kA
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In a line-commutated converter (LCC) HVDC link the thyristors conduct in one direction only, so the DC current cannot reverse. It must stay positive, flowing from System 1 to System 2 as marked.Line resistance from the given operating pointAny feasible operating point must satisfy , i.e. (algebraically).Reversing the powerWith fixed in direction, power can be reversed only by reversing the polarity of the DC voltages: System 1 then works as an inverter and System 2 as a rectifier.Checking the options- (A) , : , which would need . Not consistent with .
- (C), (D) need , which the thyristors cannot carry.
- (B) , : , giving . Consistent.
27
Q27MCQ1 markEasyBase load power plants are P: wind farms. Q: run-of-river plants. R: nuclear power plants. S: diesel power plants.Think it through. Then check your answer.Question
Base load power plants areP: wind farms.
Q: run-of-river plants.
R: nuclear power plants.
S: diesel power plants.Correct answer
(C) P, Q and R only
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Base load plants run continuously, close to their rated output, to supply the minimum (base) part of the load curve. A plant is used for base load when its running (fuel) cost is very low, or when its energy cannot be stored and must be used as it becomes available.- P: Wind farms. They have practically zero fuel cost and their energy cannot be stored, so whatever they generate is always taken by the grid as must-run generation. They therefore serve the base load.
- Q: Run-of-river plants. They have no (or very little) pondage, so the river flow has to be used as it comes or it is wasted. They run continuously and serve the base load.
- R: Nuclear power plants. They have high capital cost, very low fuel cost and cannot easily be ramped up or down, so they are run continuously at high load factor as base load plants.
- S: Diesel power plants. They have high fuel (running) cost but start quickly, so they are used as peak-load or standby plants, not base load.
28
Q28MCQ1 markEasyThe voltages developed across the and resistors shown in the figure are and respectively, with the polarity as marked. What is the power (in…Think it through. Then check your answer.Question
The voltages developed across the and resistors shown in the figure are and respectively, with the polarity as marked. What is the power (in Watt) delivered by the voltage source?
Correct answer
(A) 5
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Let be the current through the resistor and be the current through the resistor.
From the given polarities:- For the resistor, the voltage is with at N2 and at N1. Thus, current flows from N2 to N1.
- For the resistor, the voltage is with at N1 and at N2. Thus, current flows from N1 to N2.
The current leaves N1 and enters N2 through the source. Since the source has its negative terminal at N1 and positive terminal at N2, the current flows from the negative to the positive terminal inside the source.
Power delivered by the source .29
Q29NAT1 markMediumFor the given circuit, the Thevenin equivalent is to be determined. The Thevenin voltage, (in Volt), seen from terminal AB is ___________ [figure]Think it through. Then check your answer.Question
For the given circuit, the Thevenin equivalent is to be determined. The Thevenin voltage, (in Volt), seen from terminal AB is ___________
Correct answer
3.3 to 3.4
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To find the Thevenin voltage across terminals AB, we find the open-circuit voltage at AB. Let the bottom wire be the reference ground (). Let be the node voltage above the middle resistor.Applying KCL at node :
where is the current flowing towards terminal A.
Also, the current is defined as the current through the middle resistor: .
Substituting into the expression for :
Now substitute back into the KCL equation:
The Thevenin voltage is the voltage across the resistor at terminal AB:
.30
Q30MCQ1 markMediumAn inductor is connected in parallel with a capacitor as shown in the figure. [figure] As the frequency of current is increased, the impedance () of the network varies asThink it through. Then check your answer.Question
An inductor is connected in parallel with a capacitor as shown in the figure.
As the frequency of current is increased, the impedance () of the network varies asCorrect answer
(B) [figure]
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The impedance of a parallel LC circuit is given by:
The reactance is the imaginary part: .1.At low frequencies (), the denominator is positive, so (Inductive). As , . As , .2.At resonance (), the impedance is infinite (parallel resonance).3.At high frequencies (), the denominator is negative, so (Capacitive). As increases from , goes from towards .Graph B correctly depicts this transition from inductive reactance () to capacitive reactance () through a pole at the resonant frequency.31
Q31MCQ1 markMediumA separately excited DC generator has an armature resistance of and negligible armature inductance. At rated field current and rated rotor speed, its open-circuit…Think it through. Then check your answer.Question
A separately excited DC generator has an armature resistance of and negligible armature inductance. At rated field current and rated rotor speed, its open-circuit voltage is . When this generator is operated at half the rated speed, with half the rated field current, an uncharged capacitor is suddenly connected across the armature terminals. Assume that the speed remains unchanged during the transient. At what time (in microsecond) after the capacitor is connected will the voltage across it reach ?Correct answer
(B) 69.3
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1.The generated EMF of a DC generator is given by , where is the flux and is the speed.2.Assuming a linear magnetic circuit, flux is proportional to field current: . Thus, .3.At rated conditions: .4.At half speed () and half field current ():.5.When the capacitor is connected, the circuit is a simple RC charging circuit with , , and .6.The voltage across the capacitor is .7.Time constant .8.Setting :
.32
Q32MCQ1 markMediumThe self inductance of the primary winding of a single phase, , transformer is , and that of the secondary winding is . The mutual inductance between these…Think it through. Then check your answer.Question
The self inductance of the primary winding of a single phase, , transformer is , and that of the secondary winding is . The mutual inductance between these two windings is . The secondary winding of this transformer is short circuited and the primary winding is connected to a , single phase, sinusoidal voltage source. The current flowing in both the windings is less than their respective rated currents. The resistance of both windings can be neglected. In this condition, what is the effective inductance (in mH) seen by the source?Correct answer
(A) 416
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1.The voltage equations for two coupled coils are:
2.Since the secondary is short-circuited, :3.Substitute into the equation for :4.The effective inductance seen by the source is:5.Given , , and :.33
Q33MCQ1 markEasyThe primary mmf is least affected by the secondary terminal conditions in aThink it through. Then check your answer.Question
The primary mmf is least affected by the secondary terminal conditions in aCorrect answer
(C) current transformer.
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In a current transformer (CT) the primary winding is connected in series with the line whose current is being measured. The primary current is therefore fixed by the load of the main power circuit, not by the burden connected to the CT secondary. Hence the primary mmf is practically independent of the secondary terminal conditions.In power, potential and distribution transformers the primary is connected across the supply voltage. There the primary current is the magnetising current plus the reflected load current, so whenever the secondary load changes, the primary current (and hence the primary mmf) changes to balance the new secondary mmf.Answer: (C) current transformer.34
Q34MCQ1 markMediumA Bode magnitude plot for the transfer function of a plant is shown in the figure. Which one of the following transfer functions best describes the plant? [figure]Think it through. Then check your answer.Question
A Bode magnitude plot for the transfer function of a plant is shown in the figure. Which one of the following transfer functions best describes the plant?
Correct answer
(D) (s+1000)/(10(s+10))
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Read the plot- Low-frequency level: .
- High-frequency level: .
- The magnitude starts falling at about (a pole) and stops falling at about (a zero), with a dB/dec slope in between: over two decades.
- (A) : but (rising plot). Rejected.
- (B), (C) contain a factor in the denominator, so as . Rejected.
- (D) : , , pole at , zero at . Matches.
35
Q35MCQ1 markEasyFor the signal-flow graph shown in the figure, which one of the following expressions is equal to the transfer function ? [figure]Think it through. Then check your answer.Question
For the signal-flow graph shown in the figure, which one of the following expressions is equal to the transfer function ?
Correct answer
(B) (G₂)/(1+G₁(1+G₂))
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Label the nodes along the forward line: (where enters), (after the branch of gain ), (after , where enters), (after ), then . The two feedback branches of gain go from back to and from back to .With , apply Mason's gain formula from to .Forward path: , gain .Loops:- : , gain .
- : , gain .
36
Q36MCQ2 marksHardThe maximum value of "" such that the matrix has three linearly independent real eigenvectors isThink it through. Then check your answer.Question
The maximum value of "" such that the matrix has three linearly independent real eigenvectors isCorrect answer
(B) 13√(3)
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Characteristic equationWhy the eigenvalues must be real and distinctFor any , the first two rows of , and , are linearly independent (the third entry of the first row is while that of the second is , and the second row is non-zero). So and every eigenvalue has only one independent eigenvector. Three independent real eigenvectors therefore require three distinct real eigenvalues.Condition for three distinct real rootsPut : . Then at .- : local maximum .
- : local minimum .
37
Q37NAT2 marksMediumA solution of the ordinary differential equation is such that and . The value of…Think it through. Then check your answer.Question
A solution of the ordinary differential equation is such that and . The value of is ________.Correct answer
-3 to -3
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The characteristic equation for the differential equation is .
Solving for :
.
The general solution is .
Using the initial condition :
.
Using the condition :
.
Equating the two expressions for :
.
Then .
The solution is .
The derivative is .
At , .38
Q38MCQ2 marksMediumThe signum function is given by The Fourier series expansion of hasThink it through. Then check your answer.Question
The signum function is given byThe Fourier series expansion of hasCorrect answer
(D) only cosine terms with odd numbered harmonics.
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Let .1.Even/Odd Symmetry: Since is an even function, is also an even function (). Even functions contain only cosine terms in their Fourier series expansion ().2.Half-Wave Symmetry: Check if . The period of is , so ..
Functions with half-wave symmetry contain only odd harmonics ().
Combining these, the Fourier series expansion has only cosine terms with odd numbered harmonics.39
Q39MCQ2 marksEasyTwo players, A and B, alternately keep rolling a fair dice. The person to get a six first wins the game. Given that player A starts the game, the probability that A wins the game…Think it through. Then check your answer.Question
Two players, A and B, alternately keep rolling a fair dice. The person to get a six first wins the game. Given that player A starts the game, the probability that A wins the game isCorrect answer
(D) 6/11
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Let be the probability of rolling a six, . Let be the probability of not rolling a six, .
Player A wins if they roll a six on their 1st turn, or if both A and B fail on their 1st turns and A rolls a six on their 2nd turn, and so on.
This is an infinite geometric series with first term and common ratio .
.40
Q40MCQ2 marksMediumAn unbalanced DC Wheatstone bridge is shown in the figure. At what value of will the magnitude of be maximum? [figure]Think it through. Then check your answer.Question
An unbalanced DC Wheatstone bridge is shown in the figure. At what value of will the magnitude of be maximum?
Correct answer
(A) √((1+x))
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The output voltage of the Wheatstone bridge is given by:To find the value of that maximizes , we differentiate with respect to and set it to zero:Taking the square root on both sides:Thus, the magnitude of is maximum when .41
Q41NAT2 marksMediumThe circuit shown is meant to supply a resistive load from two separate DC voltage sources. The switches S1 and S2 are controlled so that only one of them is ON at any…Think it through. Then check your answer.Question
The circuit shown is meant to supply a resistive load from two separate DC voltage sources. The switches S1 and S2 are controlled so that only one of them is ON at any instant. S1 is turned on for and S2 is turned on for in a switching cycle time period. Assuming continuous conduction of the inductor current and negligible ripple on the capacitor voltage, the output voltage (in Volt) across is ________.
Correct answer
7 to 7
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In steady state, the average voltage across the inductor is zero. The voltage at the input of the filter, , alternates between the two source voltages depending on which switch is ON.
Given:- for
- for
- Total period
42
Q42MCQ2 marksEasyA self commutating switch SW, operated at duty cycle is used to control the load voltage as shown in the figure [figure] Under steady state operating conditions, the…Think it through. Then check your answer.Question
A self commutating switch SW, operated at duty cycle is used to control the load voltage as shown in the figureUnder steady state operating conditions, the average voltage across the inductor and the capacitor respectively, are
Correct answer
(A) V_L = 0 and V_C = (1)/(1-δ) V_(dc)
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Step 1: Average inductor voltage in steady stateIn periodic steady state the inductor current returns to the same value at the end of every switching cycle, so the net volt-seconds applied to over one period must be zero:Step 2: Identify the two sub-intervalsThe inductor is in series with the source and the switch SW is across the node feeding the diode , so this is a boost (step-up) chopper.- SW ON, for : the node is pulled to the negative rail, is reverse biased, and the full source appears across the inductor:
- SW OFF, for : the inductor current is forced through into the capacitor and the load, so the node sits at the capacitor voltage:
43
Q43NAT2 marksHardThe single-phase full-bridge voltage source inverter (VSI), shown in figure, has an output frequency of . It uses unipolar pulse width modulation with switching…Think it through. Then check your answer.Question
The single-phase full-bridge voltage source inverter (VSI), shown in figure, has an output frequency of . It uses unipolar pulse width modulation with switching frequency of and modulation index of . For , , , and , the amplitude of the fundamental component in the output voltage (in Volt) under steady-state is ________.
Correct answer
60 to 64
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1.Fundamental component of the inverter output voltage for unipolar PWM is given by .2.The filter transfer function is .3.At fundamental frequency , .4.Calculate impedances: .5.Calculate .6.Magnitude of transfer function: .7.Amplitude of fundamental component in : .44
Q44NAT2 marksMediumA 3-phase square wave (6-step) VSI feeds a 3-phase, 4 pole induction motor. The VSI line voltage has a dominant harmonic component. If the operating slip…45
Q45MCQ2 marksEasyConsider a discrete time signal given by The region of convergence of its Z-transform would beThink it through. Then check your answer.Question
Consider a discrete time signal given byThe region of convergence of its Z-transform would beCorrect answer
(C) the annular region between the two circles, both centered at origin and having radii 0.25 and 0.5
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1.The first term is a right-sided sequence. Its ROC is .2.The second term is a left-sided sequence. Its ROC is .3.The overall ROC is the intersection of the individual ROCs: .4.This represents an annular region between circles of radii and .46
Q46NAT2 marksMediumA parallel plate capacitor is partially filled with glass of dielectric constant as shown below. The dielectric strengths of air and glass are and…Think it through. Then check your answer.Question
A parallel plate capacitor is partially filled with glass of dielectric constant as shown below. The dielectric strengths of air and glass are and , respectively. The maximum voltage (in kilovolts), which can be applied across the capacitor without any breakdown, is ______.
Correct answer
17 to 20
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Let the thickness of the air layer be and the glass layer be . The dielectric constants are (air) and (glass). From the boundary condition for normal electric flux density, .We check for breakdown in both materials:1.If air breaks down first: . Then . Since (glass breakdown strength), the glass is safe. The voltage is .2.If glass breaks down first: . Then . Since , the air would have already broken down.Thus, the maximum voltage that can be applied is .47
Q47NAT2 marksMediumThe figure shows a digital circuit constructed using negative edge triggered J-K flip flops. Assume a starting state of . This state will repeat…Think it through. Then check your answer.Question
The figure shows a digital circuit constructed using negative edge triggered J-K flip flops. Assume a starting state of . This state will repeat after ______ number of cycles of the clock CLK.
Correct answer
6 to 6
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Step 1: Read the connectionsAll three J-K flip-flops are negative-edge triggered.- FF0: , clocked by CLK, so toggles on every falling edge of CLK.
- FF1: , , clocked by .
- FF2: , , clocked by .
(On each falling edge of both FF1 and FF2 respond to the values present before that edge.)Step 3: CountThe circuit is a mod-6 counter: the sequence is traversed and the starting state reappears at the end of the clock pulse.Answer: 6CLK pulse edge Action on FF1 () Action on FF2 () 1 (rising) none none 001 2 (falling) : toggle to 1 : reset, stays 0 010 3 none none 011 4 : toggle to 0 : toggle to 1 100 5 none none 101 6 : reset, stays 0 : reset to 0 000 48
Q48MCQ2 marksMediumis a maxterm representation of a Boolean function where is the MSB and is the LSB. The equivalent…Think it through. Then check your answer.Question
is a maxterm representation of a Boolean function where is the MSB and is the LSB. The equivalent minimized representation of this function isCorrect answer
(A) (A + C + D)(A + B + D)
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The given maxterm list is . This implies the minterms are the remaining values: . To find the minimized Product of Sums (POS) form, we can minimize the maxterms of the function. However, the standard interpretation of such GATE questions is to find the minimized POS for the function whose maxterms are (or equivalently, whose minterms are the 12 values listed). If we take maxterms as :
Grouping and gives .
Grouping and gives .The minimized POS is , which matches option A.49
Q49MCQ2 marksMediumThe op-amp shown in the figure has a finite gain and an infinite input resistance. A step-voltage is applied at the input at time as shown.…Think it through. Then check your answer.Question
The op-amp shown in the figure has a finite gain and an infinite input resistance. A step-voltage is applied at the input at time as shown. Assuming that the operational amplifier is not saturated, the time constant (in millisecond) of the output voltage is
Correct answer
(A) 1001
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Step 1: Node equation with a finite-gain op-ampLet be the voltage at the inverting input. The non-inverting input is grounded and the gain is finite, soThe input resistance is infinite, so the current through all flows into . In the -domain:Step 2: Transfer functionThis is a first-order system, so the output is a single exponential with time constant(the Miller-multiplied capacitance charging through ).Step 3: Substitute, , :Answer: (A) 100150
Q50MCQ2 marksMediumAn 8-bit, unipolar Successive Approximation Register type ADC is used to convert 3.5 V to digital equivalent output. The reference voltage is +5 V. The output of the ADC, at the…Think it through. Then check your answer.Question
An 8-bit, unipolar Successive Approximation Register type ADC is used to convert 3.5 V to digital equivalent output. The reference voltage is +5 V. The output of the ADC, at the end of 3rd clock pulse after the start of conversion, isCorrect answer
(A) 1010 0000
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In an 8-bit SAR ADC with , the conversion process proceeds bit by bit from MSB to LSB.1.Clock Pulse 1: The MSB () is set to 1. The DAC output is . Since , remains 1. Current state: .2.Clock Pulse 2: The next bit () is set to 1. The DAC output is . Since , is reset to 0. Current state: .3.Clock Pulse 3: The next bit () is set to 1. The DAC output is . Since , remains 1. Current state: .At the end of the 3rd clock pulse, the output is .51
Q51NAT2 marksMediumConsider the economic dispatch problem for a power plant having two generating units. The fuel costs in Rs/MWh along with the generation limits for the two units are given below:…Think it through. Then check your answer.Question
Consider the economic dispatch problem for a power plant having two generating units. The fuel costs in Rs/MWh along with the generation limits for the two units are given below: ;
; The incremental cost (in Rs/MWh) of the power plant when it supplies 200 MW is ________.Correct answer
20 to 20
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The incremental fuel costs for the two units are:Total demand .Check the incremental costs at the lower limits:
At , .
At , .Since , we should ideally load unit 2 more and unit 1 less. However, unit 1 is already at its minimum limit of . To satisfy the total demand of , we must have:
and .At this operating point, the incremental cost of the plant is determined by the unit that would meet the next increment in demand. Since unit 1 is at its lower limit and unit 2 is within its limits (), any small increase in demand will be met by unit 2.
Therefore, the incremental cost of the plant is:52
Q52MCQ2 marksEasyDetermine the correctness or otherwise of the following Assertion [a] and the Reason [r]. Assertion: Fast decoupled load flow method gives approximate load flow solution because…Think it through. Then check your answer.Question
Determine the correctness or otherwise of the following Assertion [a] and the Reason [r].Assertion: Fast decoupled load flow method gives approximate load flow solution because it uses several assumptions.Reason: Accuracy depends on the power mismatch vector tolerance.Correct answer
(D) [a] is false and [r] is true.
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Examining the assertionIn the fast decoupled load flow (FDLF) method the approximations are made only while building the Jacobian: the - and - sub-problems are decoupled and the constant matrices and are formed by assuming , and .The mismatch equations that are actually driven to zero,are the exact power-flow equations. An approximate Jacobian only changes the search direction, i.e. the number of iterations needed, not the point the iteration converges to. Hence the converged FDLF solution is not an approximate solution, and the assertion is false.Examining the reasonThe iteration is stopped when every element of the power mismatch vector falls below a prescribed tolerance . How close the final bus voltages and angles are to the true solution is therefore decided by that tolerance - a tighter gives a more accurate answer. The reason is a true statement (and it is in fact the statement that explains why the FDLF result is as accurate as one wants it to be).Conclusion[a] is false and [r] is true, so option (D) is the correct choice. Options (A) and (B) are ruled out because they require [a] to be true, and (C) is ruled out because [r] is true.Answer: (D) [a] is false and [r] is true.53
Q53NAT2 marksHardA generating unit has -constant of . The machine is initially operating in steady state at synchronous speed, and producing of…Think it through. Then check your answer.Question
A generating unit has -constant of . The machine is initially operating in steady state at synchronous speed, and producing of real power. The initial value of the rotor angle is , when a bolted three phase to ground short circuit fault occurs at the terminal of the generator. Assuming the input mechanical power to remain at , the value of in degrees, second after the fault is ________.Correct answer
5.7 to 6.1
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Step 1: Write the swing equationWith in electrical radians and all quantities in per unit,Step 2: Electrical power during the faultA bolted three-phase-to-ground fault at the generator terminals makes the terminal voltage zero, so no power can be delivered:Step 3: Angular accelerationThis is constant, so the angle grows as a parabola.Step 4: Integrate twiceThe machine starts at synchronous speed, so andAt :Step 5: Rotor angle after 0.02 sAnswer:54
Q54MCQ2 marksMediumA sustained three-phase fault occurs in the power system shown in the figure. The current and voltage phasors during the fault (on a common reference), after the natural…Think it through. Then check your answer.Question
A sustained three-phase fault occurs in the power system shown in the figure. The current and voltage phasors during the fault (on a common reference), after the natural transients have died down, are also shown. Where is the fault located?
Correct answer
(B) Location Q
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Step 1: What the reference directions meanIn the one-line diagram the positive direction of is into the upper line and that of is into the lower line, both at the left-hand bus (). The positive directions of (upper line) and (lower line) are likewise into the lines, at the right-hand bus (). On the upper line Q is near the left end and S near the right end; R is on the lower line; P is on the left source side, outside both lines.Step 2: Use the relative phase of the two end currents of each line- A healthy line simply carries through-current: what enters at one end leaves at the other, so with both reference arrows pointing into the line its two end currents are nearly apart.
- A faulted line is fed from both ends towards the fault, so both of its end currents point into the line and are roughly in phase with each other.
55
Q55NAT2 marksMediumThe circuit shown in the figure has two sources connected in series. The instantaneous voltage of the AC source (in Volt) is given by . If the circuit is in…Think it through. Then check your answer.Question
The circuit shown in the figure has two sources connected in series. The instantaneous voltage of the AC source (in Volt) is given by . If the circuit is in steady state, then the rms value of the current (in Ampere) flowing in the circuit is ______.
Correct answer
9.9 to 10.1
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The circuit contains two sources: an AC source and a DC source . By the superposition principle:1.DC Analysis: Under steady state, the inductor acts as a short circuit. The DC current is:2.AC Analysis: The AC source is , so and . The RMS value of the AC voltage is . The impedance is . The magnitude of the impedance is . The RMS value of the AC current is:3.Total RMS Current: The total RMS current is the square root of the sum of the squares of the individual RMS components:56
Q56NAT2 marksMediumIn a linear two-port network, when is applied to Port 1, a current of flows through Port 2 when it is short-circuited. When is applied to…Think it through. Then check your answer.Question
In a linear two-port network, when is applied to Port 1, a current of flows through Port 2 when it is short-circuited. When is applied to Port 1, a current of flows through a resistance connected across Port 2. When is applied to Port 1, the current (in Ampere) through a resistance connected across Port 2 is ______.Correct answer
0.4 to 0.6
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Let the Thévenin equivalent of the linear two-port network seen from Port 2 be and . Since the network is linear, is proportional to the input voltage , i.e., .1.Case 1: , Port 2 is short-circuited (), .2.Case 2: , , .Substituting :Then .3.Case 3: , .The current is:57
Q57NAT2 marksMediumIn the given circuit, the parameter is positive, and the power dissipated in the resistor is . The value of is ______. [figure]Think it through. Then check your answer.Question
In the given circuit, the parameter is positive, and the power dissipated in the resistor is . The value of is ______.
Correct answer
0.48 to 0.52
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Step 1: Magnitude of from the given powerWith the marked polarity ( on the source side), the current flowing from the source through the resistor into the middle node is . The power alone does not fix the sign of , so keep it as for now.Step 2: Current in the right-hand branchThe resistor is in series with the current source (arrow pointing down), so this branch carries exactly , leaving the middle node through the resistor.Step 3: Current in the middle branchThe resistor is in series with the dependent current source , so this branch carries exactly , directed upwards into the middle node (as the arrow shows). The resistor does not change this current; it only sets the voltage across the branch.Step 4: KCL at the middle nodeCurrents entering = currents leaving:- :
- : , which is ruled out because is positive.
58
Q58NAT2 marksMediumA separately excited DC motor runs at on no load when its armature terminals are connected to a DC source and the rated voltage is applied to the…Think it through. Then check your answer.Question
A separately excited DC motor runs at on no load when its armature terminals are connected to a DC source and the rated voltage is applied to the field winding. The armature resistance of this motor is . The no-load armature current is negligible. With the motor developing its full load torque, the armature voltage is set so that the rotor speed is . When the load torque is reduced to of the full load value under the same armature voltage conditions, the speed rises to . Neglecting the rotational losses, the full load armature current (in Ampere) is _______.Correct answer
8 to 8
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1.At no load: , , . Back EMF .2.Since field voltage is constant, flux is constant. . The constant .3.At full load torque : speed , armature voltage . Back EMF .4.The armature voltage equation is .5.Torque . When load torque is reduced to , .6.At load: speed , same armature voltage . Back EMF .7.The armature voltage equation is .8.Equating the two expressions for :.59
Q59NAT2 marksMediumA DC motor has the following specifications: , , ; flux/pole , number of poles , number of conductors ,…Think it through. Then check your answer.Question
A DC motor has the following specifications: , , ; flux/pole , number of poles , number of conductors , number of parallel paths . Armature resistance . The armature reaction is negligible and rotational losses are . The motor operates from a DC supply. If the motor runs at , the output torque produced (in Nm) is _______.Correct answer
57 to 58
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1.Calculate the back EMF :2.Calculate the armature current :3.Calculate the power developed :4.Calculate the output power by subtracting rotational losses:5.Calculate the output torque :.60
Q60NAT2 marksMediumA , , two-winding transformer is rated at . Its windings are connected as an auto-transformer of rating . A…Think it through. Then check your answer.Question
A , , two-winding transformer is rated at . Its windings are connected as an auto-transformer of rating . A resistive load of is connected to the high voltage () side of the auto-transformer. The value of equivalent load resistance (in Ohm) as seen from low voltage side is _______.Correct answer
1.3 to 1.4
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1.For an auto-transformer, the voltage ratio is .2.Given and , the ratio is .3.The impedance transformation from the high voltage side to the low voltage side is given by:4.Substituting the given values:.61
Q61NAT2 marksMediumTwo single-phase transformers and each rated at are operated in parallel. Percentage impedances of and are and ,…Think it through. Then check your answer.Question
Two single-phase transformers and each rated at are operated in parallel. Percentage impedances of and are and , respectively. To share a load of at lagging power factor, the contribution of (in kVA) is ________.Correct answer
554 to 556
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The load shared by transformer in parallel operation is given by:where is the total load, and are the percentage impedances of the transformers.
Given:
at pf lagging.
Note that .
Substituting these into the formula:The magnitude of the contribution of is approximately .62
Q62MCQ2 marksHardIn the signal flow diagram given in the figure, and are possible inputs whereas and are possible outputs. When would the SISO system derived from this…Think it through. Then check your answer.Question
In the signal flow diagram given in the figure, and are possible inputs whereas and are possible outputs. When would the SISO system derived from this diagram be controllable and observable?
Correct answer
(B) When u₂ is the only input and y₁ is the only output.
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Step 1: Write the state model from the diagramTaking the outputs of the two blocks as the states and , the branch gains givesoStep 2: Controllability of each single inputFor alone:The two columns are parallel, so the system is not controllable from .For alone:So the system is controllable from .Step 3: Observability of each single outputFor :So the system is observable from .For :So the system is not observable from ( is a left eigenvector of , both eigenvalues being ).Step 4: CombineOnly the pairing input with output makes the resulting SISO system both controllable and observable.Answer: (B) When is the only input and is the only output.63
Q63MCQ2 marksMediumThe transfer function of a second order real system with a perfectly flat magnitude response of unity has a pole at . List all the poles and zeroes.Think it through. Then check your answer.Question
The transfer function of a second order real system with a perfectly flat magnitude response of unity has a pole at . List all the poles and zeroes.Correct answer
(D) Poles at (2 ± j3), zeroes at (-2 ± j3).
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A system with a perfectly flat magnitude response of unity is an all-pass filter. For a real system, the transfer function must have poles and zeros in complex conjugate pairs. For an all-pass filter, if there is a pole at , there must be a zero at .
Given a pole at :1.Since the system is real, there must be a conjugate pole at .2.The corresponding zeros for an all-pass filter are:64
Q64MCQ2 marksEasyFind the transfer function of the system given below. [figure]Think it through. Then check your answer.Question
Find the transfer function of the system given below.
Correct answer
(C) (G₁+G₂)/(1+H(G₁+G₂))
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Step 1: Write the signals at the two summing junctionsThe output is fed back through and subtracted at both input summing junctions, so each of and receives the same error signal:Step 2: Output summing junctionStep 3: Solve for This is a negative-feedback loop whose forward path is the parallel combination .Answer: (C)65
Q65MCQ2 marksMediumThe open loop poles of a third order unity feedback system are at . Let the frequency corresponding to the point where the root locus of the system transits to unstable…Think it through. Then check your answer.Question
The open loop poles of a third order unity feedback system are at . Let the frequency corresponding to the point where the root locus of the system transits to unstable region be . Now suppose we introduce a zero in the open loop transfer function at , while keeping all the earlier open loop poles intact. Which one of the following is TRUE about the point where the root locus of the modified system transits to unstable region?Correct answer
(D) Root locus of modified system never transits to unstable region
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The question uses for a frequency, so let the loop gain be below.Step 1: Original systemThe Routh row is , which vanishes at . The auxiliary equation gives , so the root locus crosses into the right-half plane at . This is the frequency the question calls .Step 2: Add a zero atStep 3: ConclusionThe first column is positive for every . There is no sign change and no row of zeros, so no closed-loop pole ever reaches the -axis. The root locus of the modified system never crosses into the unstable region. Options (A)-(C), which assume a crossing frequency, do not apply.Answer: (D) Root locus of modified system never transits to unstable regionCol 1 Col 2 1 3 0