The PYQ practice room
GATE EE 2018 Set 1
All 65 solved GATE EE 2018 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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General Aptitude (GA)
101
Q1MCQ1 markEasy“Since you have gone off the ______, the _______ sand is likely to damage the car.” The words that best fill the blanks in the above sentence areThink it through. Then check your answer.Question
“Since you have gone off the ______, the _______ sand is likely to damage the car.”The words that best fill the blanks in the above sentence areCorrect answer
(A) course, coarse
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The first blank refers to a path or route, which is 'course'. The second blank refers to rough or large-grained sand, which is 'coarse'. Therefore, the correct pair is 'course, coarse'.2
Q2MCQ1 markEasy“A common misconception among writers is that sentence structure mirrors thought; the more _________ the structure, the more complicated the ideas.” The word that best fills the…Think it through. Then check your answer.Question
“A common misconception among writers is that sentence structure mirrors thought; the more _________ the structure, the more complicated the ideas.”The word that best fills the blank in the above sentence isCorrect answer
(D) convoluted
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The sentence suggests a parallel between the complexity of the structure and the complexity of the ideas. 'Convoluted' means extremely complex and difficult to follow, which fits the context of 'more complicated ideas'.3
Q3MCQ1 markEasyThe three roots of the equation are . What are the three values of for which ?Think it through. Then check your answer.Question
The three roots of the equation are . What are the three values of for which ?Correct answer
(D) 1, 3, 6
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Given roots of are .
For , the argument must equal the original roots:
1)
2)
3)
So the values are .4
Q4MCQ1 markMediumFor what values of k given below is an integer?Think it through. Then check your answer.Question
For what values of k given below is an integer?Correct answer
(C) 4, 8, 28
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Let the given expression be .
For to be an integer, we can simplify the expression. Let's substitute , which means . Then .The expression becomes:
For to be an integer, is an integer (since and is an integer from the options). Therefore, must also be an integer.
This implies that must be a divisor of 25.The divisors of 25 are .We can find the corresponding values of using :- If , then .
- If , then .
- If , then .
- If , then .
- If , then .
- If , then .
(A) 4, 8, 18: 18 is not in our set of possible values.
(B) 4, 10, 16: 10 and 16 are not in our set of possible values.
(C) 4, 8, 28: All three values (4, 8, 28) are in our set of possible values.
(D) 8, 26, 28: 26 is not in our set of possible values.Therefore, the correct set of values is given in option (C).5
Q5MCQ1 markEasyFunctions and are defined as follows: and , where represents the absolute value of . What would be the value…Think it through. Then check your answer.Question
Functions and are defined as follows:
and , where represents the absolute value of .
What would be the value of ?Correct answer
(A) 2
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Given the functions:
Step 1: Calculate
Step 2: Calculate
Step 3: Calculate
Thus, the value is 2.6
Q6MCQ2 marksMediumAn e-mail password must contain three characters. The password has to contain one numeral from 0 to 9, one upper case and one lower case character from the English alphabet. How…Think it through. Then check your answer.Question
An e-mail password must contain three characters. The password has to contain one numeral from 0 to 9, one upper case and one lower case character from the English alphabet. How many distinct passwords are possible?Correct answer
(C) 40,560
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The password consists of 3 characters: one numeral, one uppercase letter, and one lowercase letter.1.Selection of characters:- Number of ways to choose one numeral (0-9) = 10
- Number of ways to choose one uppercase letter (A-Z) = 26
- Number of ways to choose one lowercase letter (a-z) = 26
2.Arrangement of characters:The three chosen characters can be arranged in ways.
.3.Total distinct passwords:Total passwords = (Ways to choose) (Ways to arrange) = .Therefore, the correct option is (C).7
Q7MCQ2 marksEasyIn a certain code, AMCF is written as EQGJ and NKUF is written as ROYJ. How will DHLP be written in that code?Think it through. Then check your answer.Question
In a certain code, AMCF is written as EQGJ and NKUF is written as ROYJ. How will DHLP be written in that code?Correct answer
(C) HLPT
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The coding pattern is a shift of +4 for each letter in the alphabet:8
Q8MCQ2 marksMediumA class of twelve children has two more boys than girls. A group of three children are randomly picked from this class to accompany the teacher on a field trip. What is the…Think it through. Then check your answer.Question
A class of twelve children has two more boys than girls. A group of three children are randomly picked from this class to accompany the teacher on a field trip. What is the probability that the group accompanying the teacher contains more girls than boys?- A.0
- B.
- C.
- D.
Answer checking is unavailable for this question. You can review the published solution without a score.
Correct answer
(MARKS TO ALL)
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1.Determine the number of boys () and girls ():Total children = 12
Given: and .
Substituting in the first equation: .
Then, .2.Calculate the total number of ways to pick 3 children from 12:Since the children are picked from a finite class, this is sampling without replacement.
Total ways = .3.Identify the favorable outcomes (more girls than boys):In a group of 3, 'more girls than boys' occurs in two cases:- Case 1: 3 girls and 0 boys.
- Case 2: 2 girls and 1 boy.
Total favorable ways = .4.Calculate the probability:Probability = .5.Conclusion:None of the given options match the mathematically correct value of . If the problem were incorrectly modeled as sampling with replacement (binomial distribution), the probability would be:
.
This matches option (B). However, because the selection is from a finite group without replacement, the question is flawed. Consequently, the official GATE answer key marks this question as Marks to All.- A.
9
Q9MCQ2 marksMediumA designer uses marbles of four different colours for his designs. The cost of each marble is the same, irrespective of the colour. The table below shows the percentage of marbles…Think it through. Then check your answer.Question
A designer uses marbles of four different colours for his designs. The cost of each marble is the same, irrespective of the colour. The table below shows the percentage of marbles of each colour used in the current design. The cost of each marble increased by 25%. Therefore, the designer decided to reduce equal numbers of marbles of each colour to keep the total cost unchanged. What is the percentage of blue marbles in the new design?Blue Black Red Yellow 40% 25% 20% 15% Correct answer
(C) 43.75
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1.Initial State:Assume total marbles = 100.
Blue = 40, Black = 25, Red = 20, Yellow = 15.
Let initial cost per marble = 1 unit. Total cost = 100 units.2.New State:New cost per marble = units.
To keep total cost at 100 units, the new total number of marbles must be:
marbles.3.Reduction:Total reduction in marbles = marbles.
Since equal numbers of marbles of each of the 4 colours are reduced:
Reduction per colour = marbles.4.New Blue Marble Percentage:New number of blue marbles = .
New total marbles = 80.
Percentage of blue marbles = .10
Q10MCQ2 marksMediumP, Q, R and S crossed a lake in a boat that can hold a maximum of two persons, with only one set of oars. The following additional facts are available. (i) The boat held two…Think it through. Then check your answer.Question
P, Q, R and S crossed a lake in a boat that can hold a maximum of two persons, with only one set of oars. The following additional facts are available.
(i) The boat held two persons on each of the three forward trips across the lake and one person on each of the two return trips.
(ii) P is unable to row when someone else is in the boat.
(iii) Q is unable to row with anyone else except R.
(iv) Each person rowed for at least one trip.
(v) Only one person can row during a trip.Who rowed twice?Correct answer
(C) R
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To solve this, we first determine the total number of rowing instances. There are 3 forward trips (2 people each) and 2 return trips (1 person each), totaling 5 trips. Since only one person rows per trip, there are 5 rowing instances. With 4 people (P, Q, R, S) each rowing at least once, exactly one person must row twice ().Constraints Analysis:1.P can only row when alone, which means P can only row during one of the two return trips.2.Q can only row when with R. This means Q must row a forward trip with R as the passenger.3.R and S have no specific restrictions other than the general ones.Step-by-step Trip Reconstruction:- Trip 1 (Forward): {Q, R} cross. Q rows. (Rowing count: Q=1)
- Trip 2 (Return): R returns alone. R rows. (Rowing count: Q=1, R=1)
- Trip 3 (Forward): {P, R} cross. R rows. (Rowing count: Q=1, R=2). Note: P cannot row here as he is not alone.
- Trip 4 (Return): P returns alone. P rows. (Rowing count: Q=1, R=2, P=1)
- Trip 5 (Forward): {S, P} cross. S rows. (Rowing count: Q=1, R=2, P=1, S=1)
- All 4 people are now across the lake.
- P rowed once (alone).
- Q rowed once (with R).
- S rowed once.
- R rowed twice.
- Total rowing instances = .
ELECTRICAL ENGINEERING
5511
Q11MCQ1 markEasyA single-phase 100 kVA, 1000 V / 100 V, 50 Hz transformer has a voltage drop of 5% across its series impedance at full load. Of this, 3% is due to resistance. The percentage…Think it through. Then check your answer.Question
A single-phase 100 kVA, 1000 V / 100 V, 50 Hz transformer has a voltage drop of 5% across its series impedance at full load. Of this, 3% is due to resistance. The percentage regulation of the transformer at full load with 0.8 lagging power factor isCorrect answer
(A) 4.8
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Given:
Voltage drop across series impedance,
Voltage drop across resistance,
We know that
(or 4%)
Power factor lagging
Percentage regulation for lagging power factor is given by:
Thus, the correct option is (A).12
Q12MCQ1 markEasyIn a salient pole synchronous motor, the developed reluctance torque attains the maximum value when the load angle in electrical degrees isThink it through. Then check your answer.Question
In a salient pole synchronous motor, the developed reluctance torque attains the maximum value when the load angle in electrical degrees isCorrect answer
(B) 45
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The reluctance torque in a salient pole synchronous machine is given by:where is the load angle.
To find the maximum value of , we maximize :
Thus, the reluctance torque is maximum when the load angle is .13
Q13MCQ1 markMediumA single phase fully controlled rectifier is supplying a load with an anti-parallel diode as shown in the figure. All switches and diodes are ideal. Which one of the following is…Think it through. Then check your answer.Question
A single phase fully controlled rectifier is supplying a load with an anti-parallel diode as shown in the figure. All switches and diodes are ideal. Which one of the following is true for instantaneous load voltage and current?
Correct answer
(C) vₒ ≥ 0 & iₒ ≥ 0
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In the given circuit, a freewheeling diode (anti-parallel diode) is connected across the load.1.Load Voltage (): The freewheeling diode conducts whenever the load voltage tries to go negative (due to the inductive nature of the load when thyristors are turned off). This clamps the load voltage to approximately zero during those intervals. Therefore, the instantaneous load voltage can never be negative, i.e., .2.Load Current (): The thyristors in the full-bridge rectifier and the freewheeling diode only allow current to flow in one direction through the load (downwards in the diagram). Unidirectional switches ensure that the current cannot reverse. Therefore, .Thus, and , which corresponds to option (C).14
Q14MCQ1 markMediumFour power semiconductor devices are shown in the figure along with their relevant terminals. The device(s) that can carry dc current continuously in the direction shown when…Think it through. Then check your answer.Question
Four power semiconductor devices are shown in the figure along with their relevant terminals. The device(s) that can carry dc current continuously in the direction shown when gated appropriately is (are)
Correct answer
(B) Triac and MOSFET
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Thyristor and GTO are unidirectional devices that can only conduct current from Anode to Cathode. In the figure, the current is shown flowing from Cathode to Anode for both, so they cannot conduct. The Triac is a bidirectional device and can conduct in both directions. The MOSFET (specifically the power MOSFET shown) has an intrinsic body diode that allows current to flow from Source to Drain, and the channel can also be turned on to conduct in both directions. Thus, Triac and MOSFET can carry the current in the direction shown.15
Q15MCQ1 markEasyTwo wattmeter method is used for measurement of power in a balanced three-phase load supplied from a balanced three-phase system. If one of the wattmeters reads half of the other…Think it through. Then check your answer.Question
Two wattmeter method is used for measurement of power in a balanced three-phase load supplied from a balanced three-phase system. If one of the wattmeters reads half of the other (both positive), then the power factor of the load isCorrect answer
(D) 0.866
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In the two-wattmeter method for a balanced 3-phase load, the readings are and . Given . The phase angle is found using: . Thus, . The power factor is .16
Q16MCQ1 markMediumConsider a lossy transmission line with and as the sending and receiving end voltages, respectively. and are the series impedance and reactance of the line,…Think it through. Then check your answer.Question
Consider a lossy transmission line with and as the sending and receiving end voltages, respectively. and are the series impedance and reactance of the line, respectively. The steady-state stability limit for the transmission line will beCorrect answer
(B) less than (V₁ V₂)/(X)
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For a lossless line (), the maximum power (steady-state stability limit) is . For a lossy line with resistance , the series impedance is . The maximum power delivered is . Since and there is an additional subtractive term due to resistance, the stability limit for a lossy line is always less than .17
Q17MCQ1 markEasyThe graph of a network has 8 nodes and 5 independent loops. The number of branches of the graph isThink it through. Then check your answer.Question
The graph of a network has 8 nodes and 5 independent loops. The number of branches of the graph isCorrect answer
(B) 12
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For a connected graph, the number of independent loops is related to the number of branches and nodes by the formula:Given:- Number of nodes,
- Number of independent loops,
18
Q18MCQ1 markHardIn the figure, the voltages are , and . The circuit is in sinusoidal steady…Think it through. Then check your answer.Question
In the figure, the voltages are , and . The circuit is in sinusoidal steady state, and . , and are the average power outputs. Which one of the following statements is true?
Correct answer
(C) P₁ < 0, P₂ 0, P₃ < 0
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The average power output from a voltage source to another source through a purely inductive impedance (since ) is given by:Converting the given voltages to phasor form:- (since )
- (since )
19
Q19MCQ1 markEasyMatch the transfer functions of the second-order systems with the nature of the systems given below. | Transfer functions | Nature of system | | :--- | :--- | | P:…Think it through. Then check your answer.Question
Match the transfer functions of the second-order systems with the nature of the systems given below.Transfer functions Nature of system P: I: Overdamped Q: II: Critically damped R: III: Underdamped Correct answer
(C) P-III, Q-II, R-I
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For a second-order system with characteristic equation , the damping ratio is calculated as where is the coefficient of and is the constant term.- For P: . . Since , the system is Underdamped (III).
- For Q: . . Since , the system is Critically damped (II).
- For R: . . Since , the system is Overdamped (I).
20
Q20MCQ1 markMediumA positive charge of nC is placed at where all dimensions are in metres. Consider the plane to be a conducting ground plane. Take…Think it through. Then check your answer.Question
A positive charge of nC is placed at where all dimensions are in metres. Consider the plane to be a conducting ground plane. Take F/m. The component of the E field at is closest toCorrect answer
(D) -999.09 V/m
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According to the method of images, a conducting ground plane at can be replaced by an image charge placed at for a point charge placed at .The electric field at any point is the vector sum of the fields due to the original charge and the image charge.
Given:
nC C
F/m
Point of interest The -component of the electric field is given by:At with :The value is closest to V/m. Thus, option (D) is correct.21
Q21MCQ1 markEasyLet be a real-valued function of a real variable defined as for , and for . Which one of the following statements is true?Think it through. Then check your answer.Question
Let be a real-valued function of a real variable defined as for , and for . Which one of the following statements is true?Correct answer
(D) f(x) is differentiable but its first derivative is not differentiable at x = 0.
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Given the function:
1. Continuity at :
Since , is continuous at .2. Differentiability at :
Since , is differentiable at and .3. Continuity of at :
For ,
For ,
So, for all .
Thus, is continuous at .4. Differentiability of at :
The derivative of at is:
Since the left-hand and right-hand derivatives of at are not equal (), is not differentiable at .Conclusion: is differentiable at , but its first derivative is not differentiable at . This matches option (D).22
Q22MCQ1 markEasyThe value of the directional derivative of the function at the point (2, -1, 1) in the direction of the vector…Think it through. Then check your answer.Question
The value of the directional derivative of the function at the point (2, -1, 1) in the direction of the vector isCorrect answer
(A) 1
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The directional derivative of a function at a point in the direction of a vector is given by , where is the unit vector in the direction of .1.Calculate the gradient :2.Evaluate the gradient at the point (2, -1, 1):At :So, .3.Find the unit vector in the direction of :4.Calculate the directional derivative (dot product):Therefore, the value of the directional derivative is 1.23
Q23MCQ1 markMediumThe value of the integral in counter clockwise direction around a circle C of radius 1 with center at the point z = -2 isThink it through. Then check your answer.Question
The value of the integral in counter clockwise direction around a circle C of radius 1 with center at the point z = -2 isCorrect answer
(A) (π i)/(2)
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The given integral is .
The integrand is .
The singularities of the function are at and .The contour C is a circle of radius 1 with center at the point . The equation of the contour is , which is .We need to determine which singularities lie inside the contour C.1.For the pole at : We check if it satisfies .. Since , the pole lies outside the contour C.2.For the pole at : We check if it satisfies .. Since , the pole lies inside the contour C.Since there is a simple pole inside the contour, we can use Cauchy's Integral Formula, which states:
, provided is analytic inside and on the contour C.We can rewrite the integral as:
Here, and .
The function is analytic everywhere except at . Since is outside the contour C, is analytic inside and on C.Now, we apply the formula:
Therefore, the value of the integral is:
Alternatively, using the Residue Theorem:
The only pole inside C is at .
The residue at the simple pole is:
So, .Both methods yield the same result.
The correct option is (A).24
Q24MCQ1 markEasyIn the logic circuit shown in the figure, Y is given by [figure]Think it through. Then check your answer.Question
In the logic circuit shown in the figure, Y is given by
Correct answer
(D) Y = AB + CD
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Let's analyze the given logic circuit step-by-step.1.The first gate is a 2-input NAND gate with inputs A and B. The output of this gate, let's call it , is given by:2.The second gate is also a 2-input NAND gate with inputs C and D. The output of this gate, let's call it , is given by:3.The third gate takes the outputs of the first two gates, and , as its inputs. The symbol shown is for a 2-input AND gate. The output Y would be:Now, let's examine the given options. None of the options directly match the expression . This suggests there might be a typographical error in the question's diagram.Let's consider the possibility that the third gate was intended to be an OR gate instead of an AND gate. An OR gate symbol has a curved input side, whereas the diagram shows a flat input side (AND gate).If we assume the third gate is an OR gate, the output Y would be:
This expression exactly matches option (D).Given that this is a common type of exam question, it's highly likely that the diagram contains a typo and the final gate should have been an OR gate. Based on this assumption, option (D) is the correct answer.25
Q25MCQ1 markMediumThe op-amp shown in the figure is ideal. The input impedance is given by [figure]Think it through. Then check your answer.Question
The op-amp shown in the figure is ideal. The input impedance is given by
Correct answer
(B) -Z (R₂)/(R₁)
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For an ideal op-amp, .
The current through is .
Since the inverting input current is zero, this same current flows through .
Thus, .
The input current is the current through impedance :
.
The input impedance is .26
Q26MCQ1 markEasyA continuous-time input signal is an eigenfunction of an LTI system, if the output isThink it through. Then check your answer.Question
A continuous-time input signal is an eigenfunction of an LTI system, if the output isCorrect answer
(A) k x(t), where k is an eigenvalue
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By definition, a signal is an eigenfunction of a system if the output is a scalar multiple of the input signal. Mathematically, for a system operator , is an eigenfunction if , where is a constant (possibly complex) known as the eigenvalue. For Linear Time-Invariant (LTI) systems, complex exponentials of the form are eigenfunctions because the output is , where is the transfer function evaluated at . Therefore, if the output is , is an eigenfunction.27
Q27NAT1 markEasyConsider a non-singular square matrix A. If and , the determinant of the matrix A is _________(up to 1…Think it through. Then check your answer.Question
Consider a non-singular square matrix A. If and , the determinant of the matrix A is _________(up to 1 decimal place).Correct answer
5.5 to 5.5
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Let and be the eigenvalues of the matrix .1.The trace of a matrix is the sum of its eigenvalues:2.The eigenvalues of are and . The trace of is the sum of these eigenvalues:3.We use the algebraic identity:4.Substitute the known values:
5.The determinant of a matrix is the product of its eigenvalues:Therefore, the determinant of the matrix is 5.5.28
Q28NAT1 markMediumLet be a real-valued function of a real variable defined as , where denotes the largest integer less than or equal to . The value of…Think it through. Then check your answer.Question
Let be a real-valued function of a real variable defined as , where denotes the largest integer less than or equal to . The value of is _______ (up to 2 decimal places).Correct answer
0.49 to 0.51
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The function is the fractional part function, which is periodic with period . A property of periodic functions is that the integral over any interval of length equal to the period is constant: In this case, and . Therefore:In the interval , the greatest integer function . Thus, .
Evaluating the integral:The value of the integral is 0.5.29
Q29NAT1 markMediumIn the two-port network shown, the parameter in ohms is _____________ (up to 2 decimal…Think it through. Then check your answer.Question
In the two-port network shown, the parameter in ohms is _____________ (up to 2 decimal places).
Correct answer
0.45 to 0.55
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To find the parameter, we need to find the input impedance when the output port is short-circuited ().1.Short-circuit the output: Setting grounds the output node (Node B).2.Identify nodes: Let the node between the three resistors be Node A. The input voltage is applied at the input terminal.3.KCL at Node A:- Current enters from the left through a resistor: .
- At Node A, the currents are: (entering), (leaving towards the right through the dependent source), (leaving downwards), and (leaving towards the right through the resistor).
- KCL equation:
- .
- Substitute into the expression for : .
- .
30
Q30NAT1 markMediumThe series impedance matrix of a short three-phase transmission line in phase coordinates is…Think it through. Then check your answer.Question
The series impedance matrix of a short three-phase transmission line in phase coordinates isIf the positive sequence impedance is , and the zero sequence is , then the imaginary part of (in ) is __________ (up to 2 decimal places).Correct answer
7 to 7
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The relationship between phase impedances (, ) and sequence impedances (, , ) for a balanced transmission line is given by:1.Zero sequence impedance:2.Positive sequence impedance:3.Negative sequence impedance:We are given:
We have a system of two linear equations with two unknowns, and :
(i)
(ii) To find , we can subtract equation (i) from equation (ii):
The question asks for the imaginary part of .
.To be complete, we can also find from equation (i):
.
Let's check this with equation (ii):
, which matches the given .The imaginary part of is 7.00.31
Q31NAT1 markMediumThe positive, negative and zero sequence impedances of a 125 MVA, three-phase, 15.5 kV, star-grounded, 50 Hz generator are pu, pu and pu respectively on the…Think it through. Then check your answer.Question
The positive, negative and zero sequence impedances of a 125 MVA, three-phase, 15.5 kV, star-grounded, 50 Hz generator are pu, pu and pu respectively on the machine rating base. The machine is unloaded and working at the rated terminal voltage. If the grounding impedance of the generator is pu, then the magnitude of fault current for a b-phase to ground fault (in kA) is __________ (up to 2 decimal places).Correct answer
73 to 74
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1.Calculate Base Current ():2.Fault Current in per-unit ():For a single line-to-ground fault (whether a, b, or c phase), the magnitude of the fault current is given by:
Given:- pu (rated terminal voltage)
- pu
- pu
- pu
- pu (grounding impedance)
3.Convert to kA:The magnitude of the fault current is approximately 73.53 kA, which falls within the range [73.0, 74.0].32
Q32NAT1 markMediumA bus admittance matrix for an electric power system has non-zero elements. The minimum number of branches (transmission lines and transformers) in this…Think it through. Then check your answer.Question
A bus admittance matrix for an electric power system has non-zero elements. The minimum number of branches (transmission lines and transformers) in this system are _____ (up to 2 decimal places).Correct answer
3500 to 3500
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In a bus admittance matrix () of size , the number of non-zero elements is given by , where is the number of buses and is the number of branches (assuming no shunt branches are explicitly counted as separate branches from the bus-to-ground connections).Given:
Number of non-zero elements = Using the formula:
Thus, the minimum number of branches is 3500.33
Q33NAT1 markMediumThe waveform of the current drawn by a semi-converter from a sinusoidal AC voltage source is shown in the figure. If A, the rms value of fundamental component of the…Think it through. Then check your answer.Question
The waveform of the current drawn by a semi-converter from a sinusoidal AC voltage source is shown in the figure. If A, the rms value of fundamental component of the current is ___________A (up to 2 decimal places).
Correct answer
16.9 to 17.7
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The source current waveform of a single-phase semi-converter with a constant load current is shown in the figure. The current is for and for .From the figure, the firing angle .The fundamental component of the source current is given by:The RMS value of the fundamental component is:Using the identity :Thus, the rms value of the fundamental component of the current is approximately 17.39 A.34
Q34NAT1 markMediumA separately excited dc motor has an armature resistance . The field excitation is kept constant. At an armature voltage of , the motor…Think it through. Then check your answer.Question
A separately excited dc motor has an armature resistance . The field excitation is kept constant. At an armature voltage of , the motor produces a torque of at zero speed. Neglecting all mechanical losses, the no-load speed of the motor (in radian/s) for an armature voltage of is _____ (up to 2 decimal places).Correct answer
600 to 600
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For a separately excited DC motor:
Torque
Back EMF
Voltage equation Step 1: Find from the zero-speed condition.
At zero speed, , so .
.
Given :
.Step 2: Find no-load speed at .
At no-load, neglecting mechanical losses, .
.
.35
Q35NAT1 markEasyConsider a unity feedback system with forward transfer function given by The steady-state error in the output of the system for a unit-step input…Think it through. Then check your answer.Question
Consider a unity feedback system with forward transfer function given byThe steady-state error in the output of the system for a unit-step input is _________(up to 2 decimal places).Correct answer
0.65 to 0.69
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For a unity feedback system (), the steady-state error for a unit-step input is given by:Given the forward transfer function:Substituting the values into the error formula:Evaluating the limit as :Rounding to two decimal places, the steady-state error is 0.67.36
Q36MCQ2 marksMediumA transformer with toroidal core of permeability is shown in the figure. Assuming uniform flux density across the circular core cross-section of radius , and…Think it through. Then check your answer.Question
A transformer with toroidal core of permeability is shown in the figure. Assuming uniform flux density across the circular core cross-section of radius , and neglecting any leakage flux, the best estimate for the mean radius is
Correct answer
(D) (μ I r² N_P² ω)/(2V)
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1.Reluctance of the toroidal core:The mean path length is and the cross-sectional area is .
Reluctance .2.Inductance of the primary winding ():.3.Relationship between voltage and current:The primary voltage is and current is .
For an ideal inductor, .
.
Comparing magnitudes: .4.Solve for R:
.This matches option (D).37
Q37MCQ2 marksMediumA 0-1 Ampere moving iron ammeter has an internal resistance of and inductance of . A shunt coil is connected to extend its range to 0-10 Ampere…Think it through. Then check your answer.Question
A 0-1 Ampere moving iron ammeter has an internal resistance of and inductance of . A shunt coil is connected to extend its range to 0-10 Ampere for all operating frequencies. The time constant in milliseconds and resistance in of the shunt coil respectively areCorrect answer
(A) 2, 5.55
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1.Meter parameters:Resistance , Inductance .
Time constant of the meter .2.Condition for frequency independence:To extend the range for all frequencies, the time constant of the shunt coil () must equal the time constant of the meter ().
.3.Extension of range:Multiplying factor .
The shunt resistance is given by:
.Thus, the time constant is and the resistance is . Correct option is (A).38
Q38MCQ2 marksMediumThe positive, negative and zero sequence impedances of a three phase generator are and respectively. For a line-to-line fault with fault impedance , the…Think it through. Then check your answer.Question
The positive, negative and zero sequence impedances of a three phase generator are and respectively. For a line-to-line fault with fault impedance , the fault current is , where is the fault current with zero fault impedance. The relation between and isCorrect answer
(A) Z_f = ((Z₁+Z₂)(1-k))/(k)
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For a line-to-line fault with fault impedance , the fault current is given by:
When the fault impedance is zero (), the fault current is:
Given that , we can substitute the expressions:
Canceling from both sides:
Rearranging to solve for :
Therefore, option (A) is correct.39
Q39MCQ2 marksMediumConsider the two bus power system network with given loads as shown in the figure. All the values shown in the figure are in per unit. The reactive power supplied by generator…Think it through. Then check your answer.Question
Consider the two bus power system network with given loads as shown in the figure. All the values shown in the figure are in per unit. The reactive power supplied by generator and are and respectively. The per unit values of , and line reactive power loss () respectively are
Correct answer
(C) 6.34, 11.34, 2.68
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1.Real Power Balance:Net real power at Bus 1: pu.
Net real power at Bus 2: pu.
The real power flow from Bus 1 to Bus 2 is:
Since , we have .2.Reactive Power Flow:Reactive power flow from Bus 1 to Bus 2:
pu.
Reactive power flow from Bus 2 to Bus 1:
pu.3.Reactive Power Loss:pu.4.Generator Reactive Power:At Bus 1: pu.
At Bus 2: pu.The values are . Option (C) is correct.40
Q40MCQ2 marksMediumThe per-unit power output of a salient-pole generator which is connected to an infinite bus, is given by the expression, , where …Think it through. Then check your answer.Question
The per-unit power output of a salient-pole generator which is connected to an infinite bus, is given by the expression, , where is the load angle. Newton-Raphson method is used to calculate the value of for pu. If the initial guess is , then its value (in degree) at the end of the first iteration isCorrect answer
(C) 28.74^
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Given . We want to find for pu.
Define .
The derivative is .
Initial guess radians.Calculate :
Calculate :
Newton-Raphson update:
radians.Convert to degrees:
New value of :
.Thus, option (C) is correct.41
Q41MCQ2 marksMediumA DC voltage source is connected to a series L-C circuit by turning on the switch S at time as shown in the figure. Assume . Which one of the following…Think it through. Then check your answer.Question
A DC voltage source is connected to a series L-C circuit by turning on the switch S at time as shown in the figure. Assume . Which one of the following circular loci represents the plot of versus ?
Correct answer
(B) [figure]
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For the given series LC circuit with a DC step input :1.The voltage across the capacitor satisfies the differential equation: .2.Since , we have .3.Given , the equation becomes .4.With initial conditions and , the solution is .5.The current is .6.Squaring and adding terms to eliminate :
.7.This is the equation of a circle in the plane centered at with radius 5. This corresponds to option (B).42
Q42MCQ2 marksMediumThe equivalent impedance for the infinite ladder circuit shown in the figure is [figure]Think it through. Then check your answer.Question
The equivalent impedance for the infinite ladder circuit shown in the figure is
Correct answer
(A) j12 Ω
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Let the equivalent impedance of the infinite ladder be .1.The repeating unit consists of a series impedance and a parallel branch .2.For an infinite ladder, .3..4.
.5.Solving the quadratic equation: .6. or .7.Since the circuit is purely reactive and inductive, must be positive imaginary. Thus, .43
Q43MCQ2 marksMediumConsider a system governed by the following equations The initial conditions are such that…Think it through. Then check your answer.Question
Consider a system governed by the following equationsThe initial conditions are such that . Let and . Which one of the following is true?Correct answer
(C) x_(1f) = x_(2f) < ∞
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1.Summing the two state equations: . This implies (constant) for all . Specifically, .2.Subtracting the equations: .3.Let . Then .4.As , , which means , so .5.From the sum conservation: .6.Since and are finite, .44
Q44MCQ2 marksMediumThe number of roots of the polynomial, , in the open left half of the complex plane isThink it through. Then check your answer.Question
The number of roots of the polynomial, , in the open left half of the complex plane isCorrect answer
(A) 3
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To find the number of roots in the open left half of the complex plane (LHP), we use the Routh-Hurwitz criterion.1.Construct the Routh Array for the polynomial :Row 1 7 31 25 1 14 73 200 -7 -42 -175 0 8 48 200 0 2.Handle the Row of Zeros: Calculating the row coefficients:
Dividing by 8:3.Differentiate the Auxiliary Equation: . We use the coefficients (4, 12) to replace the row of zeros in the row.4.Complete the Routh Array:Row Col 1 Col 2 Col 3 4 12 0 24 200 0 -21.33 0 0 200 0 0 5.Analyze Sign Changes: The first column of the Routh array is: 1, 1, -7, 8, 4, 24, -21.33, 200.- Sign changes occur between: (1 and -7), (-7 and 8), (24 and -21.33), and (-21.33 and 200).
- Total sign changes = 4. This indicates 4 roots lie in the Right Half Plane (RHP).
7.Calculate LHP Roots: Total roots = 7.Roots in LHP = Total roots - RHP roots - roots = .Thus, there are 3 roots in the open left half of the complex plane.45
Q45MCQ2 marksMediumIf is a circle and , then isThink it through. Then check your answer.Question
If is a circle and , then isCorrect answer
(B) 0
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The function is .
The singularities are at and , both are poles of order 2. Both poles lie inside the circle .
By Cauchy's Residue Theorem, .Residue at :
.Residue at :
.Sum of residues = .
Therefore, .46
Q46MCQ2 marksHardWhich one of the following statements is true about the digital circuit shown in the figure [figure]Think it through. Then check your answer.Question
Which one of the following statements is true about the digital circuit shown in the figure
Correct answer
(B) It can be used for dividing the input frequency by 5.
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Let the outputs of the three D flip-flops be from left to right. The circuit is a shift register with feedback.
From the diagram:
(NAND gate feedback)
Let's trace the states :1.Start with :2.:3.:4.:5.:6.: (Cycle repeats)The main cycle is , which has a length of 5.
Checking other states:- (enters cycle)
- : (enters cycle)
- : (enters cycle)
47
Q47MCQ2 marksEasyDigital input signals with as the MSB and as the LSB are used to realize the Boolean function , where denotes the …Think it through. Then check your answer.Question
Digital input signals with as the MSB and as the LSB are used to realize the Boolean function , where denotes the minterm. In addition, has a don't care for . The simplified expression for is given byCorrect answer
(B) A + C
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The Boolean function is .
Using a 3-variable K-map:Groups:\ 00 01 11 10 0 1 () X () 1 () 1 () 1 0 () 1 () 1 () 0 () 1.A quad covering (using the don't care ): This gives .2.A quad covering (using the don't care ): This gives .Thus, the simplified expression is .48
Q48MCQ2 marksMediumConsider the two continuous-time signals defined below:…Think it through. Then check your answer.Question
Consider the two continuous-time signals defined below:These signals are sampled with a sampling period of seconds to obtain discrete-time signals and , respectively. Which one of the following statements is true?Correct answer
(A) The energy of x₁[n] is greater than the energy of x₂[n].
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The signals are sampled at . The range corresponds to .For :
for .
Energy .For :
for .
Energy .Since , the energy of is greater than the energy of .49
Q49MCQ2 marksMediumThe signal energy of the continuous-time signal isThink it through. Then check your answer.Question
The signal energy of the continuous-time signalisCorrect answer
(D) 5/3
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The signal can be written as:
The energy is given by:
.50
Q50NAT2 marksMediumThe Fourier transform of a continuous-time signal is given by where and …Think it through. Then check your answer.Question
The Fourier transform of a continuous-time signal is given bywhere and denotes frequency. Then the value of at is ___________ (up to 1 decimal place). ( denotes the logarithm to base )Correct answer
9.5 to 10.5
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Given the Fourier transform .
Using the standard Fourier transform pair , we identify .
Thus, the time-domain signal is .
At :
.
Taking the natural logarithm:
.
The absolute value is:
.51
Q51NAT2 marksMediumIn the circuit shown in the figure, the bipolar junction transistor (BJT) has a current gain . The base-emitter voltage drop is a constant, . The…Think it through. Then check your answer.Question
In the circuit shown in the figure, the bipolar junction transistor (BJT) has a current gain . The base-emitter voltage drop is a constant, . The value of the Thevenin equivalent resistance (in ) as shown in the figure is ______ (up to 2 decimal places).
Correct answer
89 to 91.5
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To find the Thevenin equivalent resistance at terminals a-b, we deactivate all independent sources (the 15 V and 10.7 V DC sources are shorted to ground).The resistance looking into the emitter of the BJT is given by:
where is the resistance in the base path.From the DC bias conditions:
.
.
.
.Calculating :
.The Thevenin resistance is the parallel combination of the emitter resistor and the resistance looking into the emitter :
.Using the approximation :
.
This value falls within the official range of 89.0 to 91.5.52
Q52NAT2 marksMediumAs shown in the figure, is the arc from the point to the point on the circle . The value of the integral…Think it through. Then check your answer.Question
As shown in the figure, is the arc from the point to the point on the circle . The value of the integral is _____ (up to 2 decimal places).
Correct answer
0 to 0
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Let and .
Check for exactness: and .
Since , the vector field is conservative and the integral is path-independent.
The potential function satisfies:
So, .
The integral is :
Value .53
Q53NAT2 marksMediumLet . The maximum value of over the interval is _______ (up to 1 decimal place).Think it through. Then check your answer.Question
Let . The maximum value of over the interval is _______ (up to 1 decimal place).Correct answer
11.5 to 12.5
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To find the maximum value of on the interval , we first find the critical points by setting the first derivative to zero:
Critical points are and . Both points lie within the interval .Now, evaluate at the boundaries and the critical points:1.At :2.At :3.At :4.At :Comparing these values, the maximum value is .54
Q54NAT2 marksMediumLet A = and , where I is the identity matrix. The determinant…Think it through. Then check your answer.Question
Let A = and , where I is the identity matrix. The determinant of B is ________ (up to 1 decimal place).Correct answer
0.9 to 1.1
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The characteristic equation of matrix A is given by :The eigenvalues of A are , , and .Given B = where . The eigenvalues of B are , , and :
The determinant of B is the product of its eigenvalues:
.55
Q55NAT2 marksMediumThe capacitance of an air-filled parallel-plate capacitor is pF. When a dielectric slab whose thickness is half the distance between the plates, is placed on one of the…Think it through. Then check your answer.Question
The capacitance of an air-filled parallel-plate capacitor is pF. When a dielectric slab whose thickness is half the distance between the plates, is placed on one of the plates covering it entirely, the capacitance becomes pF. Neglecting the fringing effects, the relative permittivity of the dielectric is _____________ (up to 2 decimal places).Correct answer
2.5 to 2.55
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Let the initial capacitance be pF.
When a dielectric slab of thickness and relative permittivity is inserted, the system acts as two capacitors in series: one with air () and one with the dielectric (). pF
pFThe equivalent capacitance is:
Given pF:56
Q56NAT2 marksMediumThe unit step response y(t) of a unity feedback system with open loop transfer function is shown in the figure. The value of K is ______ (up to…Think it through. Then check your answer.Question
The unit step response y(t) of a unity feedback system with open loop transfer function
is shown in the figure. The value of K is ______ (up to 2 decimal places).
Correct answer
8 to 8
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The system is a unity feedback system with the open-loop transfer function .
The input is a unit step, so .From the given response curve, the steady-state value of the output as is .The steady-state error for a unit step input is given by:
.For a type 0 system, the steady-state error is also given by the formula:
, where is the static position error constant. is calculated as:
.Now, we can equate the two expressions for :
.Thus, the value of K is 8.00.57
Q57NAT2 marksMediumA three-phase load is connected to a three-phase balanced supply as shown in the figure. If V, V and…Think it through. Then check your answer.Question
A three-phase load is connected to a three-phase balanced supply as shown in the figure. If V, V and V (angles are considered positive in the anti-clockwise direction), the value of R for zero current in the neutral wire is ___________ (up to 2 decimal places).
Correct answer
5.7 to 5.85
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For zero current in the neutral wire, the sum of the currents in the three phases must be zero:Given the phase voltages:
V
V
VThe currents in each phase are:
A
ASumming these currents for zero neutral current:Converting to rectangular form:The value of R is approximately 5.77 .58
Q58NAT2 marksMediumThe voltage across the circuit in the figure, and the current through it, are given by the following expressions: …Think it through. Then check your answer.Question
The voltage across the circuit in the figure, and the current through it, are given by the following expressions:
where radian/s. If the average power delivered to the circuit is zero, then the value of X (in Ampere) is ______ (up to 2 decimal places).
Correct answer
10 to 10
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The average power delivered to a circuit with periodic voltage and current is the sum of the average power of the DC components and the average power of the AC components at each harmonic frequency.The given voltage and current are:
We can separate the DC and AC components:
DC components: V, A.
AC components: V, A.The average power from the DC components is:
W.The average power from the AC components is given by , where and are the peak amplitudes and and are the phase angles.First, let's express the AC voltage in a standard cosine form:
V.
So, the peak voltage amplitude is V and its phase is .For the AC current:
.
The peak current amplitude is A and its phase is .Now, calculate the AC power:
.
Since ,
W.The total average power is the sum of DC and AC power:
.The problem states that the average power delivered to the circuit is zero, so .
.The value of X is 10.00 A.59
Q59NAT2 marksMediumA phase controlled single phase rectifier, supplied by an AC source, feeds power to an R-L-E load as shown in the figure. The rectifier output voltage has an average value given…Think it through. Then check your answer.Question
A phase controlled single phase rectifier, supplied by an AC source, feeds power to an R-L-E load as shown in the figure. The rectifier output voltage has an average value given by , where volts and is the firing angle. If the power delivered to the lossless battery is 1600 W, in degree is________ (up to 2 decimal places).
Correct answer
90 to 90
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Given:
V
Power delivered to the battery W
From the circuit, V
A
The average output voltage is also given by:
(since average voltage across the inductor is zero in steady state)
V
Equating the two expressions for :
Thus, the firing angle is .60
Q60NAT2 marksHardThe figure shows two buck converters connected in parallel. The common input dc voltage for the converters has a value of 100 V. The converters have inductors of identical value.…Think it through. Then check your answer.Question
The figure shows two buck converters connected in parallel. The common input dc voltage for the converters has a value of 100 V. The converters have inductors of identical value. The load resistance is 1 . The capacitor voltage has negligible ripple. Both converters operate in the continuous conduction mode. The switching frequency is 1 kHz, and the switch control signals are as shown. The circuit operates in the steady state. Assuming that the converters share the load equally, the average value of , the current of switch S1 (in Ampere), is _____ (up to 2 decimal places).
Correct answer
11.5 to 13.5
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Given:
Input voltage V
Load resistance
Switching frequency kHz Time period msFrom the switch control signals:
Switch S1 is ON from to ms. Duty cycle .
Switch S2 is ON from ms to ms. Duty cycle .In a buck converter, the average output voltage .
Since both converters are in parallel and share the load equally, the output voltage is determined by the duty cycle of the switches.
V.Total load current A.
Since the converters share the load equally, the average current from each converter is:
A.The average current of switch S1 () is given by:
, where is the average inductor current of the first converter.
In steady state, the average inductor current equals the average output current of that converter.
A.
A.61
Q61NAT2 marksMediumA 3-phase 900 kVA, 3 kV / kV (/Y), 50 Hz transformer has primary (high voltage side) resistance per phase of 0.3 and secondary (low voltage side)…Think it through. Then check your answer.Question
A 3-phase 900 kVA, 3 kV / kV (/Y), 50 Hz transformer has primary (high voltage side) resistance per phase of 0.3 and secondary (low voltage side) resistance per phase of 0.02 . Iron loss of the transformer is 10 kW. The full load % efficiency of the transformer operated at unity power factor is _______ (up to 2 decimal places).Correct answer
97.2 to 97.55
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1.Transformer Rating and Voltages:- Rating kVA
- Primary Voltage V (Delta connected)
- Secondary Voltage V (Star connected, phase voltage is V)
- Primary line current A.
- Primary phase current (Delta) A.
- Secondary line current A.
- Secondary phase current (Star) A.
- Total Copper Loss
- W = 14.4 kW.
- Iron Loss kW.
- Total Loss kW.
- Output Power kW.
- Efficiency
- .
62
Q62NAT2 marksMediumA 200 V DC series motor, when operating from rated voltage while driving a certain load, draws 10 A current and runs at 1000 r.p.m. The total series resistance is 1 . The…Think it through. Then check your answer.Question
A 200 V DC series motor, when operating from rated voltage while driving a certain load, draws 10 A current and runs at 1000 r.p.m. The total series resistance is 1 . The magnetic circuit is assumed to be linear. At the same supply voltage, the load torque is increased by 44%. The speed of the motor in r.p.m. (rounded to the nearest integer) is ________ .Correct answer
823 to 827
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Given:
Supply voltage
Initial armature current
Initial speed
Total series resistance Step 1: Calculate initial back EMF ()
Step 2: Determine the relationship between torque and current
For a DC series motor with a linear magnetic circuit, flux .
Torque .Step 3: Calculate new armature current ()
Given that the load torque is increased by 44%, .
Step 4: Calculate new back EMF ()
Step 5: Calculate new speed ()
We know .
Rounding to the nearest integer, the speed is 825 r.p.m.63
Q63NAT2 marksHardA dc to dc converter shown in the figure is charging a battery bank, B2 whose voltage is constant at 150 V. B1 is another battery bank whose voltage is constant at 50 V. The value…Think it through. Then check your answer.Question
A dc to dc converter shown in the figure is charging a battery bank, B2 whose voltage is constant at 150 V. B1 is another battery bank whose voltage is constant at 50 V. The value of the inductor, L is 5 mH and the ideal switch, S is operated with a switching frequency of 5 kHz with a duty ratio of 0.4. Once the circuit has attained steady state and assuming the diode D to be ideal, the power transferred from B1 to B2 (in Watt) is ___________ (up to 2 decimal places).
Correct answer
12 to 12
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The circuit is a boost converter with fixed input and output voltages.
Given:
(B1)
(B2)
Step 1: Calculate peak inductor current ()
Step 2: Determine the conduction mode
During the off-time (), the voltage across the inductor is .
The time taken for the current to reach zero is .
Since (), the converter operates in Discontinuous Conduction Mode (DCM).Step 3: Calculate average power transferred
In a lossless converter, the power transferred from B1 to B2 is equal to the average power drawn from B1.
Average current from B1 () is the average of the inductor current over one cycle:
Power transferred .64
Q64NAT2 marksHardThe equivalent circuit of a single phase induction motor is shown in the figure, where the parameters are ,…Think it through. Then check your answer.Question
The equivalent circuit of a single phase induction motor is shown in the figure, where the parameters are , and is the slip. At no-load, the motor speed can be approximated to be the synchronous speed. The no-load lagging power factor of the motor is___________ (up to 3 decimal places).
Correct answer
0.104 to 0.112
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At no-load, the slip .
Forward branch impedance : Since , . Thus, .
Backward branch impedance : At , the branch is in parallel with .
.
Total input impedance .
The power factor is .65
Q65NAT2 marksMediumThe voltage across the terminals and as shown in the figure, is a sinusoidal voltage having a frequency radian/s. When the inductor current is…Think it through. Then check your answer.Question
The voltage across the terminals and as shown in the figure, is a sinusoidal voltage having a frequency radian/s. When the inductor current is in phase with the voltage , the magnitude of the impedance (in ) seen between the terminals and is ________ (up to 2 decimal places).
Correct answer
50 to 50
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The impedance seen between terminals and is given by the series combination of the inductor and the parallel combination of the resistor and capacitor :To simplify, multiply the numerator and denominator of the second term by the complex conjugate :It is given that the current is in phase with the voltage , which means the impedance must be purely resistive. Therefore, the imaginary part of must be zero:When this condition is met, the magnitude of the impedance is equal to its real part:Given values:
First, calculate :Now, calculate the magnitude of the impedance:Thus, the magnitude of the impedance is 50.00 .