41. The shape of the current-torque current characteristics in DC series motor is a __________
A. Rectangular Hyperbolic
B. Parabola
C. Circle
D. Ellipse
Answer: B
The shape of the current-torque characteristics in the DC series motor is a parabola. The motor equation is
Eb=Vt-IaRa=Km∅ωm
T=Km∅Ia
∅∝Ia
T∝Ia2.
42. Calculate the current in DC series field winding using the following data: Ia=3 A.
A. 4 A
B. 2 A
C. 3 A
D. 6 A
Answer: C
In a DC series motor, field windings are connected in series with the armature circuit. The armature current will also flow through the series winding.
If=Ia=3 A.
43. For a given torque, increasing diverter resistance of a DC series motor causes the ________
A. decrease in speed and less armature current
B. a decrease in speed but armature current remains the same
C. increase in speed and more armature current
D. increase in speed but armature current remains the same
Answer: A
In DC series motor, increasing diverter resistance increases the field current and field flux and also decreases the armature current and therefore decreases the speed.
44. The field diverter resistance for a DC series motor is kept ________
A. High
B. Low
C. zero
D. one
Answer: B
The field diverter resistance for a DC series motor is kept low in order to increase the speed of the motor. This will reduce the field flux and increase the armature current.
45. Which braking method is the best method for obtaining high braking torque?
A. Regenerative braking
B. Plugging
C. Dynamic braking
D. Rheostatic braking
Answer: B
Plugging is the best braking method among all braking techniques. In plugging the value of the armature current reverses and the mechanical energy is extracted. A very high braking torque is produced in the case of plugging.
46. The polarity of back e.m.f changes in which of the method?
A. Plugging
B. Regenerative braking
C. Dynamic braking
D. Rheostatic braking
Answer: A
In the case of the Plugging braking technique polarity of the back e.m.f voltage changes due to which current direction changes and mechanical, and electrical energy are wasted in the form of heat in resistors.
47. Full form of WRIM.
A. Wound round induction motor
B. World cage induction motor
C. Wolf cage induction motor
D. Squirrel cage inverter motor
Answer: A
WRIM stands for wound round induction motor. WRIM rotor is made up of armature conductors. There are no copper bars or rods involved in it.
48. Calculate the energy stored in the capacitor if the voltage across the capacitor is 20 V and the capacitance value is 2 F.
A. 400 J
B. 200 J
C. 100 J
D. 50 J
Answer: A
The energy stored in the capacitor is .5×C×V2. It is the total amount of energy stored in the capacitor in the steady-state condition.
E=.5×C×V2
=.5×2×20×20=400 J.
49. Calculate the energy stored in the inductor if the current value is 4 A and the inductance value is 1 H.
A. 4 J
B. 2 J
C. 8 J
D. 5 J
Answer: C
The energy stored in the inductor is .5×L×I2. It is the total amount of energy stored in the inductor in the steady-state condition.
E=.5×L×I2
=.5×1×4×4=8 J.
50. All networks are always circuits.
A. True
B. False
Answer: B
The network is defined as the interconnection of electrical elements that may or may not has a closed path. The circuit is defined as the interconnection of an element that must have at least one closed path. All networks are not always circuits but vice-versa is true.
