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Circuit Theory and Calculations Flashcards

6 cards from real 309A practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 6 Circuit Theory and Calculations flashcards as text

  1. What is the resonant frequency of a series RLC circuit with L = 10 mH and C = 100 µF?

    Answer: 159.2 Hz

    Resonant frequency f = 1/(2π√(LC)) = 1/(2π√(0.01 × 0.0001)) = 1/(2π × 0.001) = 159.2 Hz. At resonance, XL = XC.

  2. A three-phase balanced load draws 30 A per phase at 600 V line-to-line. What is the total apparent power?

    Answer: 31.18 kVA

    For a three-phase system: S = √3 × VL × IL = 1.732 × 600 × 30 = 31,176 VA ≈ 31.18 kVA.

  3. What happens to the total capacitance when capacitors are connected in parallel?

    Answer: It increases (values add)

    When capacitors are connected in parallel, the total capacitance is the sum of individual capacitances: Ct = C1 + C2 + C3. This is opposite to how resistors behave.

  4. A motor draws 25 A at 480 V three-phase with a power factor of 0.85. What is the real power consumed?

    Answer: 17.66 kW

    Real power P = √3 × V × I × PF = 1.732 × 480 × 25 × 0.85 = 17,658 W ≈ 17.66 kW.

  5. What is the time constant of a circuit with a 500 µF capacitor and a 2 kΩ resistor?

    Answer: 1.0 s

    The time constant τ = R × C = 2000 Ω × 0.0005 F = 1.0 second. After one time constant, a capacitor charges to approximately 63.2% of the supply voltage.

  6. In a delta-connected three-phase system, what is the relationship between line current and phase current?

    Answer: IL = IP × √3

    In a delta connection, the line current is √3 (1.732) times the phase current: IL = √3 × IP. Line voltage equals phase voltage in a delta connection.