The Fourier series for the function f(x)=sin2x is:

1.  sinx + sin2x

2.  1 -cos2x

3.  sin2x + cos2x

4.  0.5-0.5cos2x

4
Correct Answer :

0.5-0.5cos2x

Explanation :
No Explanation available for this question

If u(t) is the unit step and δ(t) is the unit impulse function,the inverse z- transform of F(z)=1/(z+1) for k ≥ 0 is:

1.  (-1)k δ(k)

2.  δ(k)-(-1)k

3.  (-1)k u(k)

4.  u(k)-(-1)k

4
Correct Answer :

δ(k)-(-1)k

Explanation :
No Explanation available for this question

Two magnetic poles revolve around a stationary armature carrying two coils (c1-c’1, c2-c’2) as shown in given Fig.Consider the instant when the poles are in a position as shown.Identify the correct statement regarding the polarity of the induced emf at this instant in coil sides c1 and c2.

1.  o in c1, no emf in c2

2.  ® in c1, no emf in c2

3.  o in c2, no emf in c1

4.  ® in c2, no emf in c1

4
Correct Answer :

® in c1, no emf in c2

Explanation :
No Explanation available for this question

A 50 kW dc shunt motor is loaded to draw rated armature current at any given speed.When driven (i) at half the rated speed by armature voltage control and (ii) at 1.5 times the rated speed by field control,the respective output powers delivered by the motor are approximately

1.  25 kW in (i) and 75 kW in (ii)

2.  25 kW in (i) and 50 kW in (ii)

3.  50 kW in (i) and 75 kW in (ii)

4.  50 kW in (i) and 50 kW in (ii)

4
Correct Answer :

25 kW in (i) and 50 kW in (ii)

Explanation :
No Explanation available for this question

In relation to the synchronous machines,which one of the following statements is false

1.  In salient pole machines,the direct-axis synchronous reactance is greater than the quadrature-axis synchronous reactance

2.  The damper bars help the synchronous motor self-start

3.  Short circuit ratio is the ratio of the field current required to produce the rated voltage on open circuit to the rated armature current

4.  The V-curve of a synchronous motor represents the variation in the armature current with field excitation,at a given output power

4
Correct Answer :

Short circuit ratio is the ratio of the field current required to produce the rated voltage on open circuit to the rated armature current

Explanation :
No Explanation available for this question

Under no load condition,if the applied voltage to an induction motor is reduced from the rated voltage to half the rated value,

1.  the speed decreases and the stator current increases

2.  both the speed and the stator current decrease

3.  the speed and the stator current remain practically constant

4.  there is negligible change in the speed but the stator current decreases

4
Correct Answer :

both the speed and the stator current decrease

Explanation :
No Explanation available for this question

A three-phase cage induction motor is started by direct-on-line (DOL) switching at the rated voltage.If the starting current drawn is 6 times the full load current,and the full load slip is 4%,the ratio of the starting developed torque to the full load torque is approximately equal to

1.  0.24

2.  1.44

3.  2.40

4.  6.00

4
Correct Answer :

1.44

Explanation :
No Explanation available for this question

In a single phase induction motor driving a fan load,the reason for having a high resistance rotor is to achieve

1.  low starting torque

2.  quick acceleration

3.  high efficiency

4.  reduced size

4
Correct Answer :

quick acceleration

Explanation :
No Explanation available for this question

Assertion:Under V/f control of induction motor,the maximum value of the developed torque remains constant over a wide range of speed in the sub-synchronous region. Reason:The magnetic flux is maintained almost constant at the rated value by keeping the ratio V/f constant over the considered speed range.

1.  Both [a] and [r] are true and [r] is the correct reason for [a]

2.  Both [a] and [r] are true but [r] is not the correct reason for [a]

3.  Both [a] and [r] are false

4.  [a] is true but [r] is false

4
Correct Answer :

Both [a] and [r] are true and [r] is the correct reason for [a]

Explanation :
No Explanation available for this question

The parameters of a transposed overhead transmission line are given as:Self reactance xs=0.5Ω/Am and Mutual reactance xm=0.1Ω/km The positive sequence reactance x1 and zero sequence reactance x0, respectively,in Ω/km are

1.  0.3,0.2

2.  0.5,0.2

3.  0.5,0.6

4.  0.3, 0.6

4
Correct Answer :

0.3, 0.6

Explanation :
No Explanation available for this question

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