PC General Theory and Calculations 3

Question 1

A 120V, 60Hz circuit has an inductor with 10Ω inductive reactance. What is the inductance (L) in millihenries?

Accepted Answer

26.5 mH

Answer

XL = 2πfL → L = XL / (2πf) = 10 / (2π × 60) ≈ 26.5 mH.

Question 2

When two 100 µF capacitors are connected in series, what is the total capacitance?

Accepted Answer

50 µF

Answer

For equal capacitors in series, C_T = C/n = 100/2 = 50 µF.

Question 3

A 480V, 3-phase balanced load consumes 50 kW at 0.8 PF lagging. What is the line current?

Accepted Answer

75.1 A

Answer

I = P / (√3 × VL × PF) = 50,000 / (1.732 × 480 × 0.8) ≈ 75.1 A.

Question 4

What is the capacitive reactance of a 100 µF capacitor at 60 Hz?

Accepted Answer

26.5 Ω

Answer

XC = 1 / (2πfC) = 1 / (2π × 60 × 0.0001) ≈ 26.5 Ω.

Question 5

In a 3-phase wye (Y) system, how does line voltage relate to phase voltage?

Accepted Answer

V_line = V_phase × √3

Answer

In a wye system, line voltage is √3 (≈1.732) times the phase voltage.

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