1. What is the condition for the maximum power transfer theorem in DC circuits?
A. RL=2Rth
B. RL≠Rth
C. RL≫ Rth
D. RL=Rth
Answer: D
The condition for the maximum power transfer theorem is load should be variable and RL=Rth. During maximum power transfer conditions voltage across load becomes half of Thevenin voltage and efficiency becomes 50 %.
2. Instantaneous power in the 3-φ system is constant.
A. True
B. False
Answer: A
The 3-φ system is more economical than the 2-∅ system because of no vibrations in the power waveform. The instantaneous power in the 3-∅ system is constant.
P=3VpIpcos(φ)=√3VLILcos(∅).
3. The length of phasor is ___________
A. R.M.S
B. Average
C. Peak to Peak
D. Minimum
Answer: A
Phasors are the rotating values that rotate with some angular frequency Ω. The length of the phasor value is r.m.s value.
4. Transient analysis is only applicable to bounded systems.
A. True
B. False
Answer: A
Bounded systems are those systems that have some finite maximum value and are decaying functions. Transient analysis is only applicable to bounded signals as they achieve a steady-state after some time.
5. Calculate the velocity of the ball if the angular speed is 7 rad/s and the radius is .2 m.
A. 2.5 m/s
B. 1.4 m/s
C. 4.5 m/s
D. 1.0 m/s
Answer: B
The velocity of the ball can be calculated using the relation V=Ω×r. The velocity is the vector product of angular speed and radius.
V = Ω×r = 7×.2 = 1.4 m/s.
6. Calculate the value of the time period if the frequency of the signal is .001 Hz.
A. 1000 sec
B. 2000 sec
C. 5000 sec
D. 1500 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÷.001=1000 sec.
7. Calculate the value of the frequency of the 440 V DC supply.
A. 100 Hz
B. 0 Hz
C. 200 Hz
D. 500 Hz
Answer: B
The frequency is defined as the number of oscillations per second. It is reciprocal to the time period. DC supply magnitude is constant. It does not change with time so the frequency of DC supply is 0 Hz.
8. Calculate the value of the power factor if the values of R and Z are 2 Ω and 10 Ω.
A. 0.8
B. 0.5
C. 0.2
D. 0.4
Answer: C
The power factor is defined as the ratio of active power to apparent power.
Cos(φ)=R÷Z=2÷10=.2.
It has no unit.
9. Calculate the value of capacitor voltage during resonance condition if the value of supply voltage is 20 V and the quality factor is 3.
A. 60 V
B. 50 V
C. 10 V
D. 30 V
Answer: A
During the resonance condition XL=Xc.
The value of the capacitor voltage is Q×Vs.
The power factor of the circuit is one.
Vc=20×3=60 V.
10. When 30 A current flows into the positive terminal of current source 8 V. Calculate the power delivered by the source.
A. -240 W
B. 360 W
C. -430 W
D. 500 W
Answer: A
When the current enters the positive terminal of an element it will always absorb the power and when the current leaves the positive terminal it will deliver the power.
