1. 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
Explanation: If a circuit has complex impedance, the average power is power dissipated in resistor only and is not stored in capacitor or inductor
2. 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
Explanation: The expression of effective value of voltage is Veff = Vm/√2. Given Vm = 100. On substituting the value in the equation we get effective value of voltage = 100/√2 = 71V.
3. 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 current.
a) 9
b) 10
c) 11
d) 12
Explanation: The expression of effective value of current is Ieff = Im/√2. Given Im = 15. On substituting the value in the equation we get effective value of current = 15/√2 = 11V
4. A voltage v (t) = 100sinωt is applied to a circuit. The current flowing through the circuit is i(t) = 15sin(ωt-30⁰). Determine the average power delivered to the circuit.
a) 620
b) 630
c) 640
d) 650
Explanation: The expression of average power delivered to the circuit is Pavg = VeffIeffcosθ, θ = 30⁰. We have Veff = 71, Ieff = 11. So the average power delivered to the circuit Pavg = 71 x 11 x cos 30⁰ = 650
5. 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
Explanation: The expression of the average power delivered to the circuit is Pavg = Im2 R/2. Given Im = 5, R = 5. So the average power delivered to the circuit = 52×5/2 = 62.5W.
6. The highest power factor will be?
a) 1
b) 2
c) 3
d) 4
Explanation: The power factor is useful in determining the useful power transferred to a load. The highest power factor will be 1
7. If power factor = 1, then the current to the load is ______ with the voltage across it.
a) out of phase
b) in phase
c) 90⁰ out of phase
d) 45⁰ out of phase
Explanation: If power factor = 1, then the current to the load is in phase with the voltage across it because the expression of power factor is power factor = cosθ
8. In case of resistive load, what is the power factor?
a) 4
b) 3
c) 2
d) 1
Explanation: In case of resistive load, the power factor = 1 as the current to the load is in phase with the voltage across it
9. If power factor = 0, then the current to a load is ______ with the voltage.
a) in phase
b) out of phase
c) 45⁰ out of phase
d) 90⁰ out of phase
Explanation: If the power factor = 0, then the current to a load is 90⁰ out of phase with the voltage and it happens in case of reactive load.
10. For reactive load, the power factor is equal to?
a) 0
b) 1
c) 2
d) 3
Explanation: For reactive load, the power factor is equal to 0. Power factor = 0 when current to a load is 90⁰ out of phase with the voltage.