If the cross-sectional area of a magnetic field increases, but the flux remains the same, the flux density
A. increases
B. decreases
C. remains the same
D. doubles
Explanatory answer : B
Flux density = flux / area
So if area increases, flux density decreases.
...
Monday, November 18, 2013
When the speed at which a conductor is moved through a magnetic field is increased, the induced voltage
When the speed at which a conductor is moved through a magnetic field is increased, the induced voltage
[A] increases
[B] decreases
[C] remains constant
[D] reaches zero
Answer: A
In a generator induced emf is proportional to speed hence if speed increases,induced emf also increase...
Wednesday, November 13, 2013
Which alternator more suitable for high-speed system ?
Which alternator more suitable for high-speed system ?
A. Salient pole
B. non salient pole
C. Both (a)& (b)
D. none of these
Answer: non salient pole, because salient pole alternators are mechanically weak...
Bundled conductor are mainly used in high voltage overhead transmission lines to-(GATE-EE-2003)
Bundled conductor are mainly used in high voltage overhead transmission lines to-(GATE-EE-2003)
A. reduce transmission lossesB. increasing mechanical strength of the lineC. reduce coronaD. reduce sag
Answer: to reduce coron...
Monday, November 11, 2013
A 4 point starter is used to start and control the speed of a (GATE-EE-2011)
A 4 point starter is used to start and control the speed of a (GATE-EE-2011)
(A) dc shunt motor with armature resistance control
(B) dc shunt motor with field weakening control
(C) dc series motor
(D) dc compound motor
Answer: option (A)
The armature current of DC shunt motor
Ia = (V- Eb) /Ra.
at the time of starting, Eb = 0. If the full supply voltage is applied to the motor, it will draw a large current due to low armature resistance.
A variable resistance should be connected in series with the armature resistance to limit the starting...
Wednesday, October 30, 2013
The equivalent circuit shown represents a / an ................. Gate.
The equivalent circuit shown represents a / an ................. Gate.
A. Ex-OR
B. NOT
C. OR
D. AND
Answer:
It is an AND gate because lamp glows only when both switches are closed.
...
Simple tips to remember the phasor relationship b/W voltage and current for resistor , inductor and capacitor
Simple tips to remember the phasor relationship b/W voltage and current for resistor , inductor and capacitorRemember the word "CIVIL"In capacitor I leads VIn inductor I lags V
for pure capacitor I leads V by 90 deg
for pure inductor I lags V by 90 deg
for pure resistor I inphase with V (0 deg)
...
Tuesday, October 29, 2013
A resistance 5ohm inductance 0.02 H and capacitor 5 uf are connected in series.find the value of power factor at resonance condition.
A resistance 5ohm inductance 0.02 H and capacitor 5 uf are connected in series.find the value of power factor at resonance condition.
a. 0.6
b. 0.8
c. 0.9
d. 1
Answer:
at resonance condition,XL=XC and therefore Z=R, hence for pure resistive circuit pf will be unit...
Thursday, October 24, 2013
One of the parts ( A, B, C, D ) in the sentence given below contains an ERROR. Which one of the following is INCORRECT
GATE-EE-2012***********One of the parts ( A, B, C, D ) in the sentence given below contains an ERROR. Which one of the following is INCORRECT ?I requested that the should be given the driving test today instead of tomorrow.A. requested thatB. should be givenC. the driving testD. instead of tomorrow
Answer:
B.should be giv...
Wednesday, October 23, 2013
A 1-hp motor draws 1000 watts. What is its efficiency ?
A 1-hp motor draws 1000 watts. What is its efficiency ?
Answer:
Efficiency = output / input
Therefore, efficiency = 746 / 1000 = 0.746
Efficiency = 74.6 %&nbs...
Monday, October 21, 2013
Anna University- Tamil Nadu State Level Placement Programme” (TNSLPP) 2013-14- CTS
Posted Date: 22nd October 2013Company Name: M/s Cognizant Technology SolutionsOrganised By: Centre for University Industry Collaboration (CUIC), Anna University, ChennaiProgram Name: Tamil Nadu State Level Placement Programme” (TNSLPP) 2013-14About Program: Anna University, Chennai is organizing “Tamil Nadu State Level Placement Programme” (TNSLPP) 2013-14, for the Present Final Year (2014 Passing Out Students) studying in Self Financing Engineering Colleges of Tamil Nadu.Date of placement Program: 26th and 27th October...
For a single phase capacitor start induction motor which of the following statements is valid ? (Gate-EE-2007)
For a single phase capacitor start induction motor which of the following statements is valid ? (Gate-EE-2007)
(A) The capacitor is used for power factor improvement
(B) The direction of rotation can be changed by reversing the main winding terminals
(C) The direction of rotation cannot be changed
(D) The direction of rotation can be changed by interchanging the supply terminals
Answer: B
The direction of rotation can be changed by either...
Friday, October 18, 2013
Statement: you can always give me a ring whenever you need Which one of the following is the best inference from the above statement ?
GATE-EE-2013***********Statement: you can always give me a ring whenever you needWhich one of the following is the best inference from the above statement ?A. because i have a nice caller tune.B. because i have a better telephone facility.C. because a friend in need in a friend indeed.D. because you need not to pay towards the telephone bills when you give me a ring.
Answer: C
Because a friend in need in a friend indee...
The eddy current loss in an a-c electric motor is 100 watts at 50 Hz. Its loss at 100 Hz will be
The eddy current loss in an a-c electric motor is 100 watts at 50 Hz. Its loss at 100 Hz will be
(A) 25 watts
(B) 59 watts
(C) 100 watts
(D) 400 watts
Explanatory answer:
Eddy current losses is proportional to square of frequency
( f^2)
In thise case frequency is doubled, so the New loss proportional to (2f)^2
New loss is proportional to 4f^2
Eddy current loss at 100 HZ is = 4 times greater
...
Slip of the induction machine is 0.02 and the stator supply frequency is 50 Hz.What will be the frequency of the rotor induced emf?
Slip of the induction machine is 0.02 and the stator supply frequency is 50 Hz.What will be the frequency of the rotor induced emf?
(A) 10 Hz.
(B) 50 Hz.
(C) 1 Hz.
(D) 2500 Hz.
Explanatory answer:
S= 0.02 ; f = 50 Hz
Therefore, frequency of rotor induced emf = s f
= 0.02 x 50 = 1 ...
Monday, October 14, 2013
The starting torque of a 1-phase induction motor is
The starting torque of a 1-phase induction motor is
(A) High.
(B) Moderate.
(C) Low.
(D) Zero
Explanatory answer:
The single-phase I.M motor starting torque is zero because of the pulsating single-phase magnetic flux. The starting of the motor requires the generation of a rotating magnetic flux similar to the rotating flux in a three-phase motor.
...
Saturday, October 12, 2013
In a 3-phase synchronous motor
In a 3-phase synchronous motor
(A) the speed of stator MMF is always more than that of rotor MMF.
(B) the speed of stator MMF is always less than that of rotor MMF.
(C) the speed of stator MMF is synchronous speed while that of rotor MMF is zero.
(D) rotor and stator MMF are stationary with respect to each other.
Explanatory answer: D
Rotor & stator mmf are stationary w.r.t each other Because, Motor is magnetically locked into position...
Friday, October 11, 2013
An SCR is considered to be a semi-controlled device because (GATE-EE-2009)
An SCR is considered to be a semi-controlled device because (GATE-EE-2009)
(A) It can be turned OFF but not ON with a gate pulse.
(B) It conducts only during one half-cycle of an alternating current wave.
(C) It can be turned ON but not OFF with a gate pulse.
(D) It can be turned ON only during one half-cycle of an alternating voltage wave.
ANSWER: C
An SCR is considered to be a semi-controlled device because it can be turned ON but not OFF with a gate pulse.
...
Thursday, October 10, 2013
Match the items in List-I (To) with the items in the List-II (Use) and select the correct answer using the codes given below the lists. (GATE-EE-2009)
Match the items in List-I (To) with the items in the List-II (Use) and select the correct answer using the codes given below the lists. (GATE-EE-2009)
List-I
a. improve power factor
b. reduce the current ripples
c. increase the power flow in line
d. reduce the Ferranti effect
List-II
1. shunt reactor
2. shunt capacitor
3. series capacitor
4. series reactor
(A) a " 2, b " 3, c " 4, d " 1
(B) a " 2, b " 4, c " 3, d " 1
(C) a " 4, b " 3, c " 1, d " 2
(D) a " 4, b " 1, c " 3, d " 2
Answer: B
*.shunt capacitors are used to improve power factor
*.series...
If the signal flow graph shown in the figure has M number of forward paths P number of individual loops,then
If the signal flow graph shown in the figure has M number of forward paths P number of individual loops,then
A. M=3 ,P=3
B. M=2 ,P=3
C. M=3 ,P=4
D. M=2 ,P=4
Explanatory answer:
Forward paths:
M1=G1G2G3G4
M2=G5G6G7G8
M=2
Individual loops:
P1=G2H2
P2=G3H3
P3=G6H6
P4=G7H7
P...
A dc shunt generator has a speed of 800 rpm when delivering 20 A to the load at the terminal voltage of 220V. If the same machine is run as a motor it takes a line current of 20A from 220V supply. The speed of the machine as a motor will be
A dc shunt generator has a speed of 800 rpm when delivering 20 A to the load at the terminal voltage of 220V. If the same machine is run as a motor it takes a line current of 20A from 220V supply. The speed of the machine as a motor will be
(A) 800 rpm.
(B) more than 800 rpm.
(C) less than 800 rpm.
(D) both higher or lower than 800 rpm.
Explanatory answer:
In generator
Ng= Eg (60A / FPZ)
Eg = V + Ia Ra
In motor
Nm= Eb (60A / FPZ)
Eb = V - Ia Ra
Eg > E b for same terminal voltage
Therefore, Ng >...
Wednesday, October 9, 2013
The r.m.s. value of sinusoidal 100 V peak to peak is _________ volt.
The r.m.s. value of sinusoidal 100 V peak to peak is _________ volt.
(A) 100 √2
(B) 50√2
(C)
50
(D) 100
Explanatory answer:
For sinusoidal,
Rms value = peak value / √2
Vpeak = Vp-p / 2 = 100/2 = 50
RMS value = 50/√2
...
If magnetic flux changes from 0.8 Wb to 0.3 Wb, then change in flux is______ Wb.
If magnetic flux changes from 0.8 Wb to 0.3 Wb, then change in flux is______ Wb.
(a) 1.1
(b) 0.5
(c) -0.5
(d) -1.1
Explanatory answer:
Change in flux= 0.3-0.8
change in flux = -0...
The no.of turns of a coil is 200 and if the current is 1 amps, then MMf is ...............
The no.of turns of a coil is 200 and if the current is 1 amps, then MMf is ...............
A. 2000 AT
B. 200 AT
C.20 AT
D. 0.5 AT
Explanatory answer:
MMF= NI (AT)
MMF = 200*1 =200 ...
Tuesday, October 8, 2013
In DC generators, armature reaction is produced actually by
In DC generators, armature reaction is produced actually by
(A) Its field current.
(B) Armature conductors.
(C) Field pole winding.
(D) Load current in armature.
Explanatory answer:
Ans: D
Because load current in armature gives rise to armature mmf which react with main field mmf...
A 50 Hz, 3-phase induction motor has a full load speed of 1440 r.p.m. The number of poles of the motor are
A 50 Hz, 3-phase induction motor has a full load speed of 1440 r.p.m. The number of poles of the motor are
(A) 4.
(B) 6.
(C) 12.
(D) 8.
Explanatory answer:
We know, N = (1-S)Ns
1440 = (1-S) Ns
Therefore, Ns = 1440/(1-S)
Ns = 120F/P = 120*50/P = 6000/P
always Ns will be closer to N. i.e. 1440
Let P=2, Ns=3000 rpm (not close to N)
Let P=4, Ns=1500 rpm (close to N)
Therefore, P=4 for N=14...
Monday, October 7, 2013
Match List I(unit) with list II (equivalent unit) and select the correct answers using the codes given below the list
Match List I(unit) with list II (equivalent unit) and select the correct answers using the codes given below the list
List I List II
A. Weber 1. Ampere second per volt
B. Coulomb 2. Volt-second
C. Farad 3. Ampere-second
...
The equivalent current-source representation for a voltage-source with open circuit voltage 12 V and internal resistance 3 ohms is
The equivalent current-source representation for a voltage-source with open circuit voltage 12 V and internal resistance 3 ohms is
(A) a current-source of strength 4A in shunt with a resistance of 6Ω.
(B) a current –source of strength 4A in series with a resistance of 3Ω.
(C) a current-source of strength 4A in shunt with a resistance of 3 ohms.
(D) a current-source of strength 4A in shunt with a resistance of 36 ohms.
Explanatory answer :
A voltage source with series resistance can be transformed to a current source...
Three capacitors of value 8µF , 16µF and 32µF are connected in series, the total capacitance will be
Three capacitors of value 8µF , 16µF and 32µF are connected in series, the total capacitance will be
(A) 32/7 µF .
(B) 7.32 µF .
(C) 56 µF .
(D) 32 µF .
Explanatory answer:
For series connection of capacitors
C = C1C2C3 / ( C1C2+C2C3+C3C1)
C = 32/7 µF...
The input of an ac circuit having pf of 0.8 lag is 20 KVA. The power drawn by the circuit is .........KW
The input of an ac circuit having pf of 0.8 lag is 20 KVA. The power drawn by the circuit is .........KW
A. 12
B. 20
C. 16
D. 8
Explanatory answer:
KVA= VI*10^3
Power = VI * PF
Power drawn = KVA*PF = 20 * 0.8 = 16 K...
Wednesday, October 2, 2013
An SCR carrying a current of 5 A, the increase in load demands the anode current to rise to 50 A in 2 micro seconds. di/dt rating of SCR is 20 A per microsecond and maximum current rating is 60 A.Comment ,under this condition what happens to SCR.
An SCR carrying a current of 5 A, the increase in load demands the anode current to rise to 50 A in 2 micro seconds. di/dt rating of SCR is 20 A per microsecond and maximum current rating is 60 A.Comment ,under this condition what happens to SCR.
Explanatory answer:
given, di/dt rating of SCR = 20 A/ us
but actual di/dt = 50 A per 2 microseconds =50/2 = 25 A/ us
Thus the actual di/dt is greater than the di/dt rating of SCR. This will lead to damage of SC...
Match the pairs with respect to a thyristor
Match the pairs with respect to a thyristor
Answer:
(i)-c
(ii)-d
(iii)-b
(iv)...
The power electronic converter shown in figure has a single-pole-double-throw switch. The pole P of the switch is connected alternatively throws A and B. The converter shown is a
The power electronic converter shown in figure has a single-pole-double-throw switch. The pole P of the switch is connected alternatively throws A and B. The converter shown is a
A. step-down chopper (buck converter)
B. half-wave rectifier
C. step-up chopper (boost converter)
D. full wave rectifier. (GATE-EE-2010)
Answer: It is a step-down chopper
...
