This set of Network Theory Multiple Choice Questions & Answers (MCQs) focuses on “Average Power”.

1. The equation of the average power (P_{avg}) is?

a) (V_{m}I_{m}/2)cosθ

b) (V_{m}I_{m}/2)sinθ

c) V_{m}I_{m}cosθ

d) V_{m}I_{m}sinθ

View Answer

Explanation: To find the average value of any power function we have to take a particular time interval from t1 to t2, by integrating the function we get the average power. The equation of the average power (P

_{avg}) is P

_{avg}= (V

_{m}I

_{m}/2)cosθ.

2. Average power (P_{avg}) =?

a) V_{eff}I_{m}cosθ

b) V_{eff}I_{eff}cosθ

c) V_{m}I_{m}cosθ

d) V_{m}I_{eff}cosθ

View Answer

Explanation: To get average power we have to take the product of the effective values of both voltage and current multiplied by cosine of the phase angle between the voltage and current. The expression of average power is Average power (P

_{avg}) = V

_{eff}I

_{eff}cosθ

3. In case of purely resistive circuit, the average power is?

a) V_{m}I_{m}

b) V_{m}I_{m}/2

c) V_{m}I_{m}/4

d) V_{m}I_{m}/8

View Answer

Explanation: In case of purely resistive circuit, the phase angle between the voltage and current is zero that is θ=0⁰. Hence the average power = V

_{m}I

_{m}/2.

4. In case of purely capacitive circuit, average power = ____ and θ=___

a) 0, 0⁰

b) 1, 0⁰

c) 1, 90⁰

d) 0, 90⁰

View Answer

Explanation: In case of purely capacitive circuit, the phase angle between the voltage and current is zero that is θ=90⁰. Hence the average power = 0.

5. In case of purely inductive circuit, average power = ____ and θ=___

a) 0, 90⁰

b) 1, 90⁰

c) 1, 0⁰

d) 0, 0⁰

View Answer

Explanation: In case of purely inductive circuit, the phase angle between the voltage and current is zero that is θ=90⁰. Hence the average power = 0.

6. If a circuit has complex impedance, the average power is ______

a) power stored in inductor only

b) power stored in capacitor only

c) power dissipated in resistor only

d) power stored in inductor and power dissipated in resistor

View Answer

Explanation: If a circuit has complex impedance, the average power is power dissipated in resistor only and is not stored in capacitor or inductor.

7. A voltage v (t) = 100sinωt is applied to a circuit. The current flowing through the circuit is i(t) = 15sin( ωt-30⁰). Find the effective value of voltage.

a) 70

b) 71

c) 72

d) 73

View Answer

Explanation: The expression of effective value of voltage is V

_{eff}= V

_{m}/√2. Given V

_{m}= 100. On substituting the value in the equation we get effective value of voltage = 100/√2 = 71V.

8. Find the effective value of current in the question 7.

a) 9

b) 10

c) 11

d) 12

View Answer

Explanation: The expression of effective value of current is I

_{eff}= I

_{m}/√2. Given I

_{m}= 15. On substituting the value in the equation we get effective value of current = 15/√2=11V.

9. Determine the average power delivered to the circuit.

a) 620

b) 630

c) 640

d) 650

View Answer

Explanation: The expression of average power delivered to the circuit is P

_{avg}= V

_{eff}I

_{eff}cosθ, θ = 30⁰. We have V

_{eff}= 71, I

_{eff}= 11. So the average power delivered to the circuit P

_{avg}= 71 x 11 x cos 30⁰ = 650W.

10. Determine the average power delivered to the circuit consisting of an impedance Z = 5+j8 when the current flowing through the circuit is I = 5∠30⁰.

a) 61.5

b) 62.5

c) 63.5

d) 64.5

View Answer

Explanation: The expression of the average power delivered to the circuit is P

_{avg}= I

_{m}

^{2}R/2. Given I

_{m}= 5, R = 5.So the average power delivered to the circuit = 5

^{2}×5/2 = 62.5W.

**Sanfoundry Global Education & Learning Series – Network Theory.**

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