131. Calculate the flux produced by the DC shunt field winding using the following data: Ia=5 A, IL=11, R=2, N=4.

A. 14 Wb

B. 12 Wb

C. 17 Wb

D. 18 Wb

Answer: B

In the DC shunt motor, field windings are connected in parallel with the armature circuit.

IF=IL-Ia=11-5=6 A.

F=NIF=R∅.

IF∝∅.

∅=F÷R=12 wb.

132. The shape of the speed-armature current characteristics in the DC shunt motor is __________

A. Hyperbolic

B. Parabola

C. Negative slope linear line

D. Ellipse

Answer: C

The shape of the speed-armature current characteristics in the DC shunt motor is a negative slope linear line. The motor equation is

Eb=Vt-IaRa=Km∅ωm.

N=(Vt-IRa)/Km.

N vs Ia is a negative slope line with slope = -Ra/Km.

133. The shape of the speed-torque characteristics in the DC shunt motor is __________

A. Rectangular Hyperbolic

B. Whole x-y plane

C. Circle

D. Ellipse

Answer: A

The shape of the speed-torque characteristics in the DC shunt motor is a rectangular hyperbola. The motor equation is

Eb=Vt-IaRa=Km∅ωm.

N=(Vt/KmIa)-Ra/Km

Ia∝√T .

N∝1÷√T.

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134. DC shunt motors are used where the high _________ is required.

A. Starting torque

B. Maximum torque

C. Minimum torque

D. Breakdown torque

Answer: A

DC series motors are used where a high starting torque is required. At starting the torque produced by DC series motor is very high.

135. The shape of the current-torque characteristics in DC shunt motor is __________

A. Rectangular Hyperbola

B. Parabola

C. Straight line

D. Ellipse

Answer: C

The shape of the current-torque characteristics in the DC shunt motor is a straight line. The motor equation is

Eb=Vt-IaRa=Km∅ωm

T=Km∅Ia

∅∝If.

Torque ∝ Ia.

136. The relationship between the torque(T) and power(P) developed in the DC shunt motor is ___________ (Neglecting all the losses)

A. T ∝ √P

B. T ∝ P2

C. T ∝ ∛P

D. T ∝ P

Answer: D

The torque developed in the DC shunt motor is the ratio of power developed and the angular

speed of the motor

T=EbIa÷ωm=P÷ωm

T ∝ P.

137. The value of current at time of starting is ___________

A. High

B. Low

C. Very low

D. 0

Answer: A

At the time of starting the motor is at rest. The e.m.f developed in the motor is zero.

Ia×Ra = Vt-Eb. Ia=Vt÷Ra.

The starting current is very high about 10-15 times of full load current.

138. Calculate the bandwidth in a series RLC circuit if the frequency is 20 Hz and the quality factor is 5.

A. 2 Hz

B. 4 Hz

C. 6 Hz

D. 8 Hz

Answer: B

Bandwidth is defined as the range of frequencies for which the signal exists. Selectivity is inversely proportional to the bandwidth.

B.W(Hz)=f÷Q=20÷5=4 Hz.

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