Apparent Power is MCQ

Apparent Power MCQ1

The units of the apparent power are

1. Watts
2. VAR
3. VA
4. None

Answer: C. VA

Explanation:

The apparent power can be expressed in VA(Volt-ampere), the active power(P) can be expressed in watts, whereas reactive power can be expressed in VAR (Volt-ampere reactive).

Hence option C is the correct answer.

Apparent Power MCQ2

A source V_s=200cosωt delivers power to the load at 0.8 power factor lagging. The reactive power is 300 VAR. The apparent power supplied by the source is_______.

1. 500 VA
2. 400 VA
3. 250 VA
4. 600 VA

Answer:  A. 500 VA

Solution:

Given that, 

Reactive power (Q) = 300 VAR

Power factor cos ∅ =0.8⇒∅=36.860

Q=Ssin∅ =300

S(0.6)=300

S=500 VA

Hence option A is the correct answer.

Apparent Power MCQ3

Three-loads are connected in parallel across a single-phase, 1200 V, 50 Hz supply.

Load 1: Capacitive load, 10 kW and 40 kVAR

Load 2: Inductive load, 35 kW and 120 kVAR

Load 3: Resistive load of 15 kW

What is the total complex power of the circuit?

1. (60+j80) kVA
2. (10+j80) kVA
3. (10-j160) kVA
4. (60+j160) kVA

Answer: A.(60+j80) kVA

Solution:

Given,

For load1 which is a capacitive load, P₁=10 kW , Q₁=-40 kVAR

S₁=P₁+jQ₁=10-j40 kVA

For load2, P₂=35 kW , Q₂=120 kVAR

S₂=P₂+jQ₂=35+j120 kVA

For load3, P₃=15 kW, Q₃=0 kVAR

S₃=P₃+jQ₃=15 kVA

Total complex power in the circuit is,

S=S₁+S₂+S₃=10-j40+35+j120+15+j0=60+j80 kVA

Hence option A is the correct answer.

Apparent Power MCQ4

A 230 V source supplies power to two loads connected in parallel. One load draws 10 kW at 0.8 power factor leading, and the second load draws 10 kVA at 0.8 power factor lagging. The complex power delivered by the source is

1. (18+j1.5) kVA
2. (18-j1.5) kVA
3. (20+j1.5) kVA
4. (20-j1.5) kVA

Answer: B (18-j1.5) kVA

Solution:

Given that for load 1,

 P₁=10 kW,cos∅₁=0.8 leading 

P₁=S₁cos∅₁=10

S₁(0.8)=10

S₁=12.5 kVA

S₁=√(P₁²+Q₁²)⇒Q₁=√(S₁²-P₁²)=7.5 kVAR

S₁=(10-j7.5) kVA    (*given leading load)

For load2,

S₂=10 kVA,cos ∅2=0.8  lagging

P₂=S₂cos ∅₂=8 kW

Q₂=S₂sin ∅₂=6 kVAR

S2=8+j6 kVA    

Total complex power in the circuit is,

S=S1+S2=10-j7.5+8+j6=18-j1.5 kVA

Hence option B is the correct answer.

Apparent Power MCQ5

A voltage source of 100 V is applied to an impedance Z=(3+j4). What are the values of active power, reactive power, and apparent power respectively?

1. 1200 W, 1200 VAR and 2200 VA
2. 1600 W, 1600 VAR, and 2000 VA
3. 1200 W, 1600 VAR, and 2000 VA
4. 1600 W, 1200 VAR, and 2200 VA

Answer: C.1200 W, 1600 VAR, and 2000 VA

Solution:

Given that,

Z=(3+j4)

⇒∅=tan^-1(4/3)=53.06⁰

V=100 V

I=V/Z=100/√(3²+4²)=20 A

S=VI=200*10=2000 VA

P=VIcos ∅ =2000(0.6)=1200 W

Q=VIsin ∅ =2000(0.8)=1600 VAR

Hence option C is the correct answer.

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