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Electrical Calculations and Theory Flashcards

7 cards from real IEC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Electrical Calculations and Theory flashcards as text

  1. A 120/240V, single-phase, 3-wire service has a 20A load on phase A and a 15A load on phase B. What is the neutral current?

    Answer: 5A

    In a single-phase 3-wire system, neutral current equals the difference between the two hot-leg currents: 20 − 15 = 5A.

  2. Kirchhoff's Voltage Law (KVL) states that:

    Answer: The algebraic sum of all voltages around any closed loop equals zero

    KVL is based on conservation of energy: all voltage rises and drops around a closed loop sum to zero.

  3. A capacitor in an AC circuit causes current to:

    Answer: Lead voltage by 90°

    In a purely capacitive circuit, current leads voltage by 90° (mnemonic: ICE — current leads in capacitors).

  4. What is the resonant frequency of a series LC circuit with L = 50mH and C = 50µF?

    Answer: 31.8 Hz

    f = 1 / (2π√LC) = 1 / (2π√(0.05 × 0.00005)) ≈ 31.8 Hz.

  5. A 480V, 3-phase motor produces 50 HP output at 90% efficiency. What is the input power in kW?

    Answer: 41.4 kW

    Output = 50 × 0.746 = 37.3 kW; Input = 37.3 / 0.90 ≈ 41.4 kW.

  6. Kirchhoff's Current Law (KCL) states that:

    Answer: The sum of currents entering a node equals the sum of currents leaving it

    KCL is based on conservation of charge: current flowing into any node must equal current flowing out.

  7. What is the inductive reactance of a 0.5H inductor at 60Hz?

    Answer: 188.5Ω

    XL = 2πfL = 2π × 60 × 0.5 ≈ 188.5Ω.