# 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

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

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

® 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

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

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

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

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

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

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

Explanation :
No Explanation available for this question

1.  0.3,0.2

2.  0.5,0.2

3.  0.5,0.6

4.  0.3, 0.6

4