Unit 18 delmar review

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University of California, Merced *

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111

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Electrical Engineering

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Feb 20, 2024

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Delmar’s Unit 18 Review 1. What is the relationship of voltage and current (concerning phase angle) in a pure resistive circuit? a. In a pure resistive circuit, the voltage and current are in phase with each other. 2. What is the relationship of voltage and current (concerning phase angle) in a pure inductive circuit? a. In a pure inductive circuit, the voltage and current are 90 degrees out of phase with each other. 3. What is power factor? a. Power factor is a ratio of true power to apparent power. 4. A circuit contains a 20-ohm resistor and an inductor with an inductance of 0.093 H. If the circuit has a frequency of 60 Hz, what is the total impedance of the circuit? a. X_L = 2piFL = 2*pi*(60 Hz) * (0.093 H) = 35.1 ohms b. Z = sqrt ((20^2) + (35.1^2)) = 40.4 ohms 5. An R-L series circuit has a power factor of 86%. How many degrees are the voltage and current out of phase with each other? a. Cos (angle theta) = 0.86 b. (angle theta) = cos^-1(0.86) = 30.68 degrees out of phase 6. An R-L series circuit has an apparent power of 230 VA and a true power of 180 W. What is the reactive power? a. VARsl = sqrt (VA^2 – P^2) b. VARsl = sqrt ( (230 VA^2) – ( 180 W ^2) ) c. VARsl = 143.17 VARs 7. The resistor in an R-L series circuit has a voltage drop of 53 V, and the inductor has a voltage drop of 28 V. What is the applied voltage of the circuit? a. 53V + 28 V = 81 V 8. An R-L series circuit has a reactive power of 1234 VARs and an apparent power of 4329 VA. How many degrees are voltage and current out of phase with each other? a. Sin (angle theta) = VARs / VA b. Sin (angle theta) = 1234 VARs / 4329 VA c. (angle theta) = sin^-1(1234 VARs /4329 VA) d. (angle theta) = 16.56 degrees 9. An R-L series circuit contains a resistor and an inductor. The resistor has a value of 6.5 ohms. The circuit is connected to 120 V and has a current flow of 12 A. What is the inductive reactance of this circuit? a. X_L = E / I b. X_L = 120 V / 12 A c. X_L = 10 ohms 10. What is the voltage drop across the resistor in the circuit in question 9? a. E = I x R b. E = 12 A x 6.5 ohms c. E = 78 V

11. A phase angle meter connected in an R-L series circuit indicates that the current is 28 degrees out of phase with the voltage. What is the circuit power factor? a. PF = cos (angle theta) b. PF = cos (28 degrees) c. PF = 0.88 or 88% 12. An R-L series circuit has a power factor of 73%. If the apparent power is 560 kVA, what is the true power in the circuit? a. P = VA x PF b. P = (560,000 VA) * (0.73) c. P = 408,800 W

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