21. The slope of the I-V curve is 160°. Calculate the value of resistance.
A. .36 Ω
B. .41 Ω
C. .89 Ω
D. 2.74 Ω
Answer: D
The slope of the I-V curve is the reciprocal of the resistance. The slope given is 160° so
R=1÷tan(160°)=2.74 Ω.
The slope of the V-I curve is resistance.
22. Calculate the value of the power if voltage=4.2 V and current=10 A.
A. 42 W
B. 12 W
C. 16 W
D. 18 W
Answer: A
Power is the product of the voltage and current. It is generally expressed in terms of W.
P=vi=4.2×10=42 W.
1 horsepower=746 W.
23. 1 calorie is equal to ________
A. 4.18 J
B. 5.23 J
C. 6.23 J
D. 8 J
Answer: A
The calorie is the unit of energy. It is equal to 4.18 Joule. It is the amount of heat energy required to raise the temperature of one 1 g of water by 1° Celsius.
24. 1 Horse-power is equal to _______
A. 745.7 W
B. 741 W
C. 747.7 W
D. 740 W
Answer: A
1 Horse-power is equal to 745.7 W. It is equal to the rate at which work is done. Horse-power is the amount of work done by a horse in carrying the weight of 90 kg for 50 meters in 60 seconds.
25. Calculate the value of the time period if the frequency of the signal is 58 sec.
A. .017 sec
B. .014 sec
C. .045 sec
D. .077 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÷58=.017 sec.
26. Calculate the value of the short circuit ratio if the per-unit value of synchronous reactance is 4.2 Ω.
A. 0.26
B. 0.23
C. 0.67
D. 0.72
Answer: B
The value of the short circuit ratio determines the stability of the synchronous machine. It is inversely proportional to the per-unit value of reactance.
SCR=1÷Xs(p.u)=1÷4.2=.23.
27. Calculate the value of the short circuit ratio if the per-unit value of synchronous reactance is 1 Ω. Assume armature resistance is 0 ohm.
A. 1
B. 2
C. 3
D. 4
Answer: A
The value of the short circuit ratio determines the stability of the synchronous machine. It is inversely proportional to the per-unit value of reactance.
