1. In the chopper circuit, commutation times are _______
A. Current commutation is equal to voltage commutation
B. Current commutation is less as compared to that of voltage commutation
C. Current commutation is more as compared to that of voltage commutation
D. Both commutation techniques are not comparable
Answer: B
In the current commutation, commutation time=CVr÷Io.
In voltage commutation, commutation time= CVs÷Io.
Hence, the commutation time of the current commutation is less as compared to the voltage commutation.
2. The generated e.m.f from 4-pole armature having 1 conductor driven at 1 rev/sec having flux per pole as 10 Wb, with wave winding is ___________
A. 30 V
B. 40 V
C. 70 V
D. 20 V
Answer: D
The generated e.m.f can be calculated using the formula
Eb = Φ×Z×N×P÷60×A
Φ represents flux per pole
Z represents the total number of conductors
P represents the number of poles
A represents the number of parallel paths
N represents speed in rpm. In wave winding number of parallel paths is 2.
Eb = 10×4×1×60÷60×2 = 20 V.
3. The unit of voltage is Pascal.
A. True
B. False
Answer: B
The voltage is equal to one volt when 1 A of current flows through a 1 Ω resistor. It is mathematically represented as I×R. It is expressed in terms of a volt(V).
4. Calculate the moment of inertia of the sphere having a mass of 8.4 kg and a radius of 61 cm.
A. 3.124 kgm2
B. 3.125 kgm2
C. 4.545 kgm2
D. 5.552 kgm2
Answer: B
The moment of inertia of the egg can be calculated using the formula
I=Σmiri2.
The mass of the egg and radius is given
I=(8.4)×(.61)2=3.125 kgm2.
It depends upon the orientation of the rotational axis.
5. The most suitable control-motor application is __________
A. AC shunt motor
B. DC separately motor
C. AC one-phase induction motor
D. DC shunt motor
Answer: B
DC separately motor has definite full-load speed, so they don’t ‘run away’ when the load is suddenly thrown off provided the field circuit remains closed. The speed for any load within the operating range of the motor can be readily obtained.
6. In a DC series motor, the e.m.f developed is proportional to _______
A. N×Ia
B. N×Ia2
C. N×Ia3
D. N×Ia5
Answer: A
In a DC series motor, the e.m.f developed is equal to KmΦN. In a DC series, the motor field winding is connected in series with the armature so the flux in the field winding is proportional to the current
Eb = KmΦN α Ia×N.
7. Calculate the value of the time period if the frequency of the signal is .07 sec.
A. 14.28 sec
B. 14.31 sec
C. 14.23 sec
D. 14.78 sec
Answer: A
The time period is defined as the time after the signal repeats itself. It is expressed in second.
T = 1÷F=1÷.07=14.28 sec.
8. The slope of the V-I curve is 13.89°. Calculate the value of resistance.
A. .247 Ω
B. .345 Ω
C. .231 Ω
D. .222 Ω
Answer: A
The slope of the V-I curve is resistance.
The slope given is 13.89° so R=tan(13.89°)=.247 Ω.
It behaves like a normal resistor.
9. In a DC shunt motor, the e.m.f developed is proportional to ___________
A. Ia
B. Ia2
C. Ia3
D. Iao
Answer: D
In a DC shunt motor, the e.m.f developed is equal to KmΦN. In a DC shunt, the motor field windings are connected separately and excited by a constant DC voltage.
E = KmΦN α Ia°.
10. Calculate the power factor angle during the resonance condition.
A. 0°
B. 10°
C. 80°
D. 90°
Answer: D
During the resonance condition, the reactive power generated by the capacitor is completely absorbed by the inductor. Only active power flows in the circuit. Net reactive power is equal to zero and Φ=0°.
